split math code out of ash and into a standalone library so we can use it in any shell (like hush!)

6 files changed, 945 insertions, 726 deletions

diff --git a/shell/Config.in b/shell/Config.in
index afc4296..7daf17f 100644
--- a/shell/Config.in
+++ b/shell/Config.in
@@ -84,22 +84,6 @@ config ASH_ALIAS
 	help
 	  Enable alias support in the ash shell.
 
-config ASH_MATH_SUPPORT
-	bool "Posix math support"
-	default y
-	depends on ASH
-	help
-	  Enable math support in the ash shell.
-
-config ASH_MATH_SUPPORT_64
-	bool "Extend Posix math support to 64 bit"
-	default n
-	depends on ASH_MATH_SUPPORT
-	help
-	  Enable 64-bit math support in the ash shell. This will make
-	  the shell slightly larger, but will allow computation with very
-	  large numbers.
-
 config ASH_GETOPTS
 	bool "Builtin getopt to parse positional parameters"
 	default n
@@ -267,6 +251,22 @@ config MSH
 comment "Bourne Shell Options"
 	depends on MSH || LASH || HUSH || ASH
 
+config SH_MATH_SUPPORT
+	bool "POSIX math support"
+	default y
+	depends on ASH || HUSH
+	help
+	  Enable math support in the shell via $((...)) syntax.
+
+config SH_MATH_SUPPORT_64
+	bool "Extend POSIX math support to 64 bit"
+	default n
+	depends on SH_MATH_SUPPORT
+	help
+	  Enable 64-bit math support in the shell. This will make the shell
+	  slightly larger, but will allow computation with very large numbers.
+	  This is not in POSIX, so do not rely on this in portable code.
+
 config FEATURE_SH_EXTRA_QUIET
 	bool "Hide message on interactive shell startup"
 	default n
diff --git a/shell/Kbuild b/shell/Kbuild
index deedc24..2b461b3 100644
--- a/shell/Kbuild
+++ b/shell/Kbuild
@@ -9,3 +9,4 @@ lib-$(CONFIG_ASH)      += ash.o ash_ptr_hack.o
 lib-$(CONFIG_HUSH)     += hush.o
 lib-$(CONFIG_MSH)      += msh.o
 lib-$(CONFIG_CTTYHACK) += cttyhack.o
+lib-$(CONFIG_SH_MATH_SUPPORT) += math.o
diff --git a/shell/ash.c b/shell/ash.c
index 4f7f38f..0d3ab0f 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -17,19 +17,6 @@
  */
 
 /*
- * rewrite arith.y to micro stack based cryptic algorithm by
- * Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
- *
- * Modified by Paul Mundt <lethal@linux-sh.org> (c) 2004 to support
- * dynamic variables.
- *
- * Modified by Vladimir Oleynik <dzo@simtreas.ru> (c) 2001-2005 to be
- * used in busybox and size optimizations,
- * rewrote arith (see notes to this), added locale support,
- * rewrote dynamic variables.
- */
-
-/*
  * The following should be set to reflect the type of system you have:
  *      JOBS -> 1 if you have Berkeley job control, 0 otherwise.
  *      define SYSV if you are running under System V.
@@ -63,6 +50,7 @@
 #include <paths.h>
 #include <setjmp.h>
 #include <fnmatch.h>
+#include "math.h"
 
 #if defined SINGLE_APPLET_MAIN
 /* STANDALONE does not make sense, and won't compile */
@@ -197,6 +185,10 @@ struct globals_misc {
 #define debug optlist[15]
 #endif
 
+#if ENABLE_SH_MATH_SUPPORT
+	arith_eval_hooks_t math_hooks;
+#endif
+
 	/* trap handler commands */
 	/*
 	 * Sigmode records the current value of the signal handlers for the various
@@ -246,6 +238,7 @@ extern struct globals_misc *const ash_ptr_to_globals_misc;
 #define random_LCG         (G_misc.random_LCG        )
 #define backgndpid  (G_misc.backgndpid )
 #define job_warning (G_misc.job_warning)
+#define math_hooks  (G_misc.math_hooks )
 #define INIT_G_misc() do { \
 	(*(struct globals_misc**)&ash_ptr_to_globals_misc) = xzalloc(sizeof(G_misc)); \
 	barrier(); \
@@ -1998,7 +1991,7 @@ findvar(struct var **vpp, const char *name)
 /*
  * Find the value of a variable.  Returns NULL if not set.
  */
-static char *
+static const char *
 lookupvar(const char *name)
 {
 	struct var *v;
@@ -2024,7 +2017,7 @@ lookupvar(const char *name)
 /*
  * Search the environment of a builtin command.
  */
-static char *
+static const char *
 bltinlookup(const char *name)
 {
 	struct strlist *sp;
@@ -2637,7 +2630,7 @@ pwdcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 #define USE_SIT_FUNCTION
 #endif
 
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 static const char S_I_T[][4] = {
 #if ENABLE_ASH_ALIAS
 	{ CSPCL, CIGN, CIGN, CIGN },            /* 0, PEOA */
@@ -2681,7 +2674,7 @@ static const char S_I_T[][3] = {
 	{ CCTL, CCTL, CCTL }                    /* 14, CTLESC ... */
 #endif
 };
-#endif /* ASH_MATH_SUPPORT */
+#endif /* SH_MATH_SUPPORT */
 
 #ifdef USE_SIT_FUNCTION
 
@@ -4273,7 +4266,7 @@ cmdputs(const char *s)
 		case CTLBACKQ+CTLQUOTE:
 			str = "\"$(...)\"";
 			goto dostr;
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 		case CTLARI:
 			str = "$((";
 			goto dostr;
@@ -5258,17 +5251,8 @@ redirectsafe(union node *redir, int flags)
  * We have to deal with backquotes, shell variables, and file metacharacters.
  */
 
-#if ENABLE_ASH_MATH_SUPPORT_64
-typedef int64_t arith_t;
-#define arith_t_type long long
-#else
-typedef long arith_t;
-#define arith_t_type long
-#endif
-
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 static arith_t dash_arith(const char *);
-static arith_t arith(const char *expr, int *perrcode);
 #endif
 
 /*
@@ -5328,11 +5312,7 @@ cvtnum(arith_t num)
 	int len;
 
 	expdest = makestrspace(32, expdest);
-#if ENABLE_ASH_MATH_SUPPORT_64
-	len = fmtstr(expdest, 32, "%lld", (long long) num);
-#else
-	len = fmtstr(expdest, 32, "%ld", num);
-#endif
+	len = fmtstr(expdest, 32, arith_t_fmt, num);
 	STADJUST(len, expdest);
 	return len;
 }
@@ -5696,7 +5676,7 @@ expbackq(union node *cmd, int quoted, int quotes)
 		stackblock() + startloc));
 }
 
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 /*
  * Expand arithmetic expression.  Backup to start of expression,
  * evaluate, place result in (backed up) result, adjust string position.
@@ -5782,7 +5762,7 @@ argstr(char *p, int flag, struct strlist *var_str_list)
 		CTLVAR,
 		CTLBACKQ,
 		CTLBACKQ | CTLQUOTE,
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 		CTLENDARI,
 #endif
 		0
@@ -5819,7 +5799,7 @@ argstr(char *p, int flag, struct strlist *var_str_list)
 		length += strcspn(p + length, reject);
 		c = p[length];
 		if (c && (!(c & 0x80)
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 					|| c == CTLENDARI
 #endif
 		   )) {
@@ -5897,7 +5877,7 @@ argstr(char *p, int flag, struct strlist *var_str_list)
 			expbackq(argbackq->n, c, quotes);
 			argbackq = argbackq->next;
 			goto start;
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 		case CTLENDARI:
 			p--;
 			expari(quotes);
@@ -6291,7 +6271,7 @@ static ssize_t
 varvalue(char *name, int varflags, int flags, struct strlist *var_str_list)
 {
 	int num;
-	char *p;
+	const char *p;
 	int i;
 	int sep = 0;
 	int sepq = 0;
@@ -6324,14 +6304,13 @@ varvalue(char *name, int varflags, int flags, struct strlist *var_str_list)
 		len = cvtnum(num);
 		break;
 	case '-':
-		p = makestrspace(NOPTS, expdest);
+		expdest = makestrspace(NOPTS, expdest);
 		for (i = NOPTS - 1; i >= 0; i--) {
 			if (optlist[i]) {
-				USTPUTC(optletters(i), p);
+				USTPUTC(optletters(i), expdest);
 				len++;
 			}
 		}
-		expdest = p;
 		break;
 	case '@':
 		if (sep)
@@ -8710,7 +8689,7 @@ static int getoptscmd(int, char **);
 #if !ENABLE_FEATURE_SH_EXTRA_QUIET
 static int helpcmd(int, char **);
 #endif
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 static int letcmd(int, char **);
 #endif
 static int readcmd(int, char **);
@@ -8792,7 +8771,7 @@ static const struct builtincmd builtintab[] = {
 	{ BUILTIN_REGULAR       "jobs", jobscmd },
 	{ BUILTIN_REGULAR       "kill", killcmd },
 #endif
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 	{ BUILTIN_NOSPEC        "let", letcmd },
 #endif
 	{ BUILTIN_ASSIGN        "local", localcmd },
@@ -10935,7 +10914,7 @@ readtoken1(int firstc, int syntax, char *eofmark, int striptabs)
 					USTPUTC(c, out);
 				}
 				break;
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 			case CLP:       /* '(' in arithmetic */
 				parenlevel++;
 				USTPUTC(c, out);
@@ -10991,7 +10970,7 @@ readtoken1(int firstc, int syntax, char *eofmark, int striptabs)
 		} /* for (;;) */
 	}
  endword:
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 	if (syntax == ARISYNTAX)
 		raise_error_syntax("missing '))'");
 #endif
@@ -11168,7 +11147,7 @@ parsesub: {
 		pungetc();
 	} else if (c == '(') {  /* $(command) or $((arith)) */
 		if (pgetc() == '(') {
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 			PARSEARITH();
 #else
 			raise_error_syntax("you disabled math support for $((arith)) syntax");
@@ -11423,7 +11402,7 @@ parsebackq: {
 	goto parsebackq_newreturn;
 }
 
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 /*
  * Parse an arithmetic expansion (indicate start of one and set state)
  */
@@ -12384,7 +12363,7 @@ timescmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 	return 0;
 }
 
-#if ENABLE_ASH_MATH_SUPPORT
+#if ENABLE_SH_MATH_SUPPORT
 static arith_t
 dash_arith(const char *s)
 {
@@ -12392,7 +12371,7 @@ dash_arith(const char *s)
 	int errcode = 0;
 
 	INT_OFF;
-	result = arith(s, &errcode);
+	result = arith(s, &errcode, &math_hooks);
 	if (errcode < 0) {
 		if (errcode == -3)
 			ash_msg_and_raise_error("exponent less than 0");
@@ -12427,7 +12406,7 @@ letcmd(int argc UNUSED_PARAM, char **argv)
 
 	return !i;
 }
-#endif /* ASH_MATH_SUPPORT */
+#endif /* SH_MATH_SUPPORT */
 
 
 /* ============ miscbltin.c
@@ -12951,654 +12930,6 @@ ulimitcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 	return 0;
 }
 
-
-/* ============ Math support */
-
-#if ENABLE_ASH_MATH_SUPPORT
-
-/* Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
-
-   Permission is hereby granted, free of charge, to any person obtaining
-   a copy of this software and associated documentation files (the
-   "Software"), to deal in the Software without restriction, including
-   without limitation the rights to use, copy, modify, merge, publish,
-   distribute, sublicense, and/or sell copies of the Software, and to
-   permit persons to whom the Software is furnished to do so, subject to
-   the following conditions:
-
-   The above copyright notice and this permission notice shall be
-   included in all copies or substantial portions of the Software.
-
-   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
-   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
-   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
-   IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
-   CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
-   TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
-   SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-*/
-
-/* This is my infix parser/evaluator. It is optimized for size, intended
- * as a replacement for yacc-based parsers. However, it may well be faster
- * than a comparable parser written in yacc. The supported operators are
- * listed in #defines below. Parens, order of operations, and error handling
- * are supported. This code is thread safe. The exact expression format should
- * be that which POSIX specifies for shells. */
-
-/* The code uses a simple two-stack algorithm. See
- * http://www.onthenet.com.au/~grahamis/int2008/week02/lect02.html
- * for a detailed explanation of the infix-to-postfix algorithm on which
- * this is based (this code differs in that it applies operators immediately
- * to the stack instead of adding them to a queue to end up with an
- * expression). */
-
-/* To use the routine, call it with an expression string and error return
- * pointer */
-
-/*
- * Aug 24, 2001              Manuel Novoa III
- *
- * Reduced the generated code size by about 30% (i386) and fixed several bugs.
- *
- * 1) In arith_apply():
- *    a) Cached values of *numptr and &(numptr[-1]).
- *    b) Removed redundant test for zero denominator.
- *
- * 2) In arith():
- *    a) Eliminated redundant code for processing operator tokens by moving
- *       to a table-based implementation.  Also folded handling of parens
- *       into the table.
- *    b) Combined all 3 loops which called arith_apply to reduce generated
- *       code size at the cost of speed.
- *
- * 3) The following expressions were treated as valid by the original code:
- *       1()  ,    0!  ,    1 ( *3 )   .
- *    These bugs have been fixed by internally enclosing the expression in
- *    parens and then checking that all binary ops and right parens are
- *    preceded by a valid expression (NUM_TOKEN).
- *
- * Note: It may be desirable to replace Aaron's test for whitespace with
- * ctype's isspace() if it is used by another busybox applet or if additional
- * whitespace chars should be considered.  Look below the "#include"s for a
- * precompiler test.
- */
-
-/*
- * Aug 26, 2001              Manuel Novoa III
- *
- * Return 0 for null expressions.  Pointed out by Vladimir Oleynik.
- *
- * Merge in Aaron's comments previously posted to the busybox list,
- * modified slightly to take account of my changes to the code.
- *
- */
-
-/*
- *  (C) 2003 Vladimir Oleynik <dzo@simtreas.ru>
- *
- * - allow access to variable,
- *   used recursive find value indirection (c=2*2; a="c"; $((a+=2)) produce 6)
- * - realize assign syntax (VAR=expr, +=, *= etc)
- * - realize exponentiation (** operator)
- * - realize comma separated - expr, expr
- * - realise ++expr --expr expr++ expr--
- * - realise expr ? expr : expr (but, second expr calculate always)
- * - allow hexadecimal and octal numbers
- * - was restored loses XOR operator
- * - remove one goto label, added three ;-)
- * - protect $((num num)) as true zero expr (Manuel`s error)
- * - always use special isspace(), see comment from bash ;-)
- */
-
-#define arith_isspace(arithval) \
-	(arithval == ' ' || arithval == '\n' || arithval == '\t')
-
-typedef unsigned char operator;
-
-/* An operator's token id is a bit of a bitfield. The lower 5 bits are the
- * precedence, and 3 high bits are an ID unique across operators of that
- * precedence. The ID portion is so that multiple operators can have the
- * same precedence, ensuring that the leftmost one is evaluated first.
- * Consider * and /. */
-
-#define tok_decl(prec,id) (((id)<<5)|(prec))
-#define PREC(op) ((op) & 0x1F)
-
-#define TOK_LPAREN tok_decl(0,0)
-
-#define TOK_COMMA tok_decl(1,0)
-
-#define TOK_ASSIGN tok_decl(2,0)
-#define TOK_AND_ASSIGN tok_decl(2,1)
-#define TOK_OR_ASSIGN tok_decl(2,2)
-#define TOK_XOR_ASSIGN tok_decl(2,3)
-#define TOK_PLUS_ASSIGN tok_decl(2,4)
-#define TOK_MINUS_ASSIGN tok_decl(2,5)
-#define TOK_LSHIFT_ASSIGN tok_decl(2,6)
-#define TOK_RSHIFT_ASSIGN tok_decl(2,7)
-
-#define TOK_MUL_ASSIGN tok_decl(3,0)
-#define TOK_DIV_ASSIGN tok_decl(3,1)
-#define TOK_REM_ASSIGN tok_decl(3,2)
-
-/* all assign is right associativity and precedence eq, but (7+3)<<5 > 256 */
-#define convert_prec_is_assing(prec) do { if (prec == 3) prec = 2; } while (0)
-
-/* conditional is right associativity too */
-#define TOK_CONDITIONAL tok_decl(4,0)
-#define TOK_CONDITIONAL_SEP tok_decl(4,1)
-
-#define TOK_OR tok_decl(5,0)
-
-#define TOK_AND tok_decl(6,0)
-
-#define TOK_BOR tok_decl(7,0)
-
-#define TOK_BXOR tok_decl(8,0)
-
-#define TOK_BAND tok_decl(9,0)
-
-#define TOK_EQ tok_decl(10,0)
-#define TOK_NE tok_decl(10,1)
-
-#define TOK_LT tok_decl(11,0)
-#define TOK_GT tok_decl(11,1)
-#define TOK_GE tok_decl(11,2)
-#define TOK_LE tok_decl(11,3)
-
-#define TOK_LSHIFT tok_decl(12,0)
-#define TOK_RSHIFT tok_decl(12,1)
-
-#define TOK_ADD tok_decl(13,0)
-#define TOK_SUB tok_decl(13,1)
-
-#define TOK_MUL tok_decl(14,0)
-#define TOK_DIV tok_decl(14,1)
-#define TOK_REM tok_decl(14,2)
-
-/* exponent is right associativity */
-#define TOK_EXPONENT tok_decl(15,1)
-
-/* For now unary operators. */
-#define UNARYPREC 16
-#define TOK_BNOT tok_decl(UNARYPREC,0)
-#define TOK_NOT tok_decl(UNARYPREC,1)
-
-#define TOK_UMINUS tok_decl(UNARYPREC+1,0)
-#define TOK_UPLUS tok_decl(UNARYPREC+1,1)
-
-#define PREC_PRE (UNARYPREC+2)
-
-#define TOK_PRE_INC tok_decl(PREC_PRE, 0)
-#define TOK_PRE_DEC tok_decl(PREC_PRE, 1)
-
-#define PREC_POST (UNARYPREC+3)
-
-#define TOK_POST_INC tok_decl(PREC_POST, 0)
-#define TOK_POST_DEC tok_decl(PREC_POST, 1)
-
-#define SPEC_PREC (UNARYPREC+4)
-
-#define TOK_NUM tok_decl(SPEC_PREC, 0)
-#define TOK_RPAREN tok_decl(SPEC_PREC, 1)
-
-#define NUMPTR (*numstackptr)
-
-static int
-tok_have_assign(operator op)
-{
-	operator prec = PREC(op);
-
-	convert_prec_is_assing(prec);
-	return (prec == PREC(TOK_ASSIGN) ||
-			prec == PREC_PRE || prec == PREC_POST);
-}
-
-static int
-is_right_associativity(operator prec)
-{
-	return (prec == PREC(TOK_ASSIGN) || prec == PREC(TOK_EXPONENT)
-	        || prec == PREC(TOK_CONDITIONAL));
-}
-
-typedef struct {
-	arith_t val;
-	arith_t contidional_second_val;
-	char contidional_second_val_initialized;
-	char *var;      /* if NULL then is regular number,
-			   else is variable name */
-} v_n_t;
-
-typedef struct chk_var_recursive_looped_t {
-	const char *var;
-	struct chk_var_recursive_looped_t *next;
-} chk_var_recursive_looped_t;
-
-static chk_var_recursive_looped_t *prev_chk_var_recursive;
-
-static int
-arith_lookup_val(v_n_t *t)
-{
-	if (t->var) {
-		const char * p = lookupvar(t->var);
-
-		if (p) {
-			int errcode;
-
-			/* recursive try as expression */
-			chk_var_recursive_looped_t *cur;
-			chk_var_recursive_looped_t cur_save;
-
-			for (cur = prev_chk_var_recursive; cur; cur = cur->next) {
-				if (strcmp(cur->var, t->var) == 0) {
-					/* expression recursion loop detected */
-					return -5;
-				}
-			}
-			/* save current lookuped var name */
-			cur = prev_chk_var_recursive;
-			cur_save.var = t->var;
-			cur_save.next = cur;
-			prev_chk_var_recursive = &cur_save;
-
-			t->val = arith (p, &errcode);
-			/* restore previous ptr after recursiving */
-			prev_chk_var_recursive = cur;
-			return errcode;
-		}
-		/* allow undefined var as 0 */
-		t->val = 0;
-	}
-	return 0;
-}
-
-/* "applying" a token means performing it on the top elements on the integer
- * stack. For a unary operator it will only change the top element, but a
- * binary operator will pop two arguments and push a result */
-static int
-arith_apply(operator op, v_n_t *numstack, v_n_t **numstackptr)
-{
-	v_n_t *numptr_m1;
-	arith_t numptr_val, rez;
-	int ret_arith_lookup_val;
-
-	/* There is no operator that can work without arguments */
-	if (NUMPTR == numstack) goto err;
-	numptr_m1 = NUMPTR - 1;
-
-	/* check operand is var with noninteger value */
-	ret_arith_lookup_val = arith_lookup_val(numptr_m1);
-	if (ret_arith_lookup_val)
-		return ret_arith_lookup_val;
-
-	rez = numptr_m1->val;
-	if (op == TOK_UMINUS)
-		rez *= -1;
-	else if (op == TOK_NOT)
-		rez = !rez;
-	else if (op == TOK_BNOT)
-		rez = ~rez;
-	else if (op == TOK_POST_INC || op == TOK_PRE_INC)
-		rez++;
-	else if (op == TOK_POST_DEC || op == TOK_PRE_DEC)
-		rez--;
-	else if (op != TOK_UPLUS) {
-		/* Binary operators */
-
-		/* check and binary operators need two arguments */
-		if (numptr_m1 == numstack) goto err;
-
-		/* ... and they pop one */
-		--NUMPTR;
-		numptr_val = rez;
-		if (op == TOK_CONDITIONAL) {
-			if (!numptr_m1->contidional_second_val_initialized) {
-				/* protect $((expr1 ? expr2)) without ": expr" */
-				goto err;
-			}
-			rez = numptr_m1->contidional_second_val;
-		} else if (numptr_m1->contidional_second_val_initialized) {
-			/* protect $((expr1 : expr2)) without "expr ? " */
-			goto err;
-		}
-		numptr_m1 = NUMPTR - 1;
-		if (op != TOK_ASSIGN) {
-			/* check operand is var with noninteger value for not '=' */
-			ret_arith_lookup_val = arith_lookup_val(numptr_m1);
-			if (ret_arith_lookup_val)
-				return ret_arith_lookup_val;
-		}
-		if (op == TOK_CONDITIONAL) {
-			numptr_m1->contidional_second_val = rez;
-		}
-		rez = numptr_m1->val;
-		if (op == TOK_BOR || op == TOK_OR_ASSIGN)
-			rez |= numptr_val;
-		else if (op == TOK_OR)
-			rez = numptr_val || rez;
-		else if (op == TOK_BAND || op == TOK_AND_ASSIGN)
-			rez &= numptr_val;
-		else if (op == TOK_BXOR || op == TOK_XOR_ASSIGN)
-			rez ^= numptr_val;
-		else if (op == TOK_AND)
-			rez = rez && numptr_val;
-		else if (op == TOK_EQ)
-			rez = (rez == numptr_val);
-		else if (op == TOK_NE)
-			rez = (rez != numptr_val);
-		else if (op == TOK_GE)
-			rez = (rez >= numptr_val);
-		else if (op == TOK_RSHIFT || op == TOK_RSHIFT_ASSIGN)
-			rez >>= numptr_val;
-		else if (op == TOK_LSHIFT || op == TOK_LSHIFT_ASSIGN)
-			rez <<= numptr_val;
-		else if (op == TOK_GT)
-			rez = (rez > numptr_val);
-		else if (op == TOK_LT)
-			rez = (rez < numptr_val);
-		else if (op == TOK_LE)
-			rez = (rez <= numptr_val);
-		else if (op == TOK_MUL || op == TOK_MUL_ASSIGN)
-			rez *= numptr_val;
-		else if (op == TOK_ADD || op == TOK_PLUS_ASSIGN)
-			rez += numptr_val;
-		else if (op == TOK_SUB || op == TOK_MINUS_ASSIGN)
-			rez -= numptr_val;
-		else if (op == TOK_ASSIGN || op == TOK_COMMA)
-			rez = numptr_val;
-		else if (op == TOK_CONDITIONAL_SEP) {
-			if (numptr_m1 == numstack) {
-				/* protect $((expr : expr)) without "expr ? " */
-				goto err;
-			}
-			numptr_m1->contidional_second_val_initialized = op;
-			numptr_m1->contidional_second_val = numptr_val;
-		} else if (op == TOK_CONDITIONAL) {
-			rez = rez ?
-				numptr_val : numptr_m1->contidional_second_val;
-		} else if (op == TOK_EXPONENT) {
-			if (numptr_val < 0)
-				return -3;      /* exponent less than 0 */
-			else {
-				arith_t c = 1;
-
-				if (numptr_val)
-					while (numptr_val--)
-						c *= rez;
-				rez = c;
-			}
-		} else if (numptr_val==0)          /* zero divisor check */
-			return -2;
-		else if (op == TOK_DIV || op == TOK_DIV_ASSIGN)
-			rez /= numptr_val;
-		else if (op == TOK_REM || op == TOK_REM_ASSIGN)
-			rez %= numptr_val;
-	}
-	if (tok_have_assign(op)) {
-		char buf[sizeof(arith_t_type)*3 + 2];
-
-		if (numptr_m1->var == NULL) {
-			/* Hmm, 1=2 ? */
-			goto err;
-		}
-		/* save to shell variable */
-#if ENABLE_ASH_MATH_SUPPORT_64
-		snprintf(buf, sizeof(buf), "%lld", (arith_t_type) rez);
-#else
-		snprintf(buf, sizeof(buf), "%ld", (arith_t_type) rez);
-#endif
-		setvar(numptr_m1->var, buf, 0);
-		/* after saving, make previous value for v++ or v-- */
-		if (op == TOK_POST_INC)
-			rez--;
-		else if (op == TOK_POST_DEC)
-			rez++;
-	}
-	numptr_m1->val = rez;
-	/* protect geting var value, is number now */
-	numptr_m1->var = NULL;
-	return 0;
- err:
-	return -1;
-}
-
-/* longest must be first */
-static const char op_tokens[] ALIGN1 = {
-	'<','<','=',0, TOK_LSHIFT_ASSIGN,
-	'>','>','=',0, TOK_RSHIFT_ASSIGN,
-	'<','<',    0, TOK_LSHIFT,
-	'>','>',    0, TOK_RSHIFT,
-	'|','|',    0, TOK_OR,
-	'&','&',    0, TOK_AND,
-	'!','=',    0, TOK_NE,
-	'<','=',    0, TOK_LE,
-	'>','=',    0, TOK_GE,
-	'=','=',    0, TOK_EQ,
-	'|','=',    0, TOK_OR_ASSIGN,
-	'&','=',    0, TOK_AND_ASSIGN,
-	'*','=',    0, TOK_MUL_ASSIGN,
-	'/','=',    0, TOK_DIV_ASSIGN,
-	'%','=',    0, TOK_REM_ASSIGN,
-	'+','=',    0, TOK_PLUS_ASSIGN,
-	'-','=',    0, TOK_MINUS_ASSIGN,
-	'-','-',    0, TOK_POST_DEC,
-	'^','=',    0, TOK_XOR_ASSIGN,
-	'+','+',    0, TOK_POST_INC,
-	'*','*',    0, TOK_EXPONENT,
-	'!',        0, TOK_NOT,
-	'<',        0, TOK_LT,
-	'>',        0, TOK_GT,
-	'=',        0, TOK_ASSIGN,
-	'|',        0, TOK_BOR,
-	'&',        0, TOK_BAND,
-	'*',        0, TOK_MUL,
-	'/',        0, TOK_DIV,
-	'%',        0, TOK_REM,
-	'+',        0, TOK_ADD,
-	'-',        0, TOK_SUB,
-	'^',        0, TOK_BXOR,
-	/* uniq */
-	'~',        0, TOK_BNOT,
-	',',        0, TOK_COMMA,
-	'?',        0, TOK_CONDITIONAL,
-	':',        0, TOK_CONDITIONAL_SEP,
-	')',        0, TOK_RPAREN,
-	'(',        0, TOK_LPAREN,
-	0
-};
-/* ptr to ")" */
-#define endexpression (&op_tokens[sizeof(op_tokens)-7])
-
-static arith_t
-arith(const char *expr, int *perrcode)
-{
-	char arithval; /* Current character under analysis */
-	operator lasttok, op;
-	operator prec;
-	operator *stack, *stackptr;
-	const char *p = endexpression;
-	int errcode;
-	v_n_t *numstack, *numstackptr;
-	unsigned datasizes = strlen(expr) + 2;
-
-	/* Stack of integers */
-	/* The proof that there can be no more than strlen(startbuf)/2+1 integers
-	 * in any given correct or incorrect expression is left as an exercise to
-	 * the reader. */
-	numstackptr = numstack = alloca((datasizes / 2) * sizeof(numstack[0]));
-	/* Stack of operator tokens */
-	stackptr = stack = alloca(datasizes * sizeof(stack[0]));
-
-	*stackptr++ = lasttok = TOK_LPAREN;     /* start off with a left paren */
-	*perrcode = errcode = 0;
-
-	while (1) {
-		arithval = *expr;
-		if (arithval == 0) {
-			if (p == endexpression) {
-				/* Null expression. */
-				return 0;
-			}
-
-			/* This is only reached after all tokens have been extracted from the
-			 * input stream. If there are still tokens on the operator stack, they
-			 * are to be applied in order. At the end, there should be a final
-			 * result on the integer stack */
-
-			if (expr != endexpression + 1) {
-				/* If we haven't done so already, */
-				/* append a closing right paren */
-				expr = endexpression;
-				/* and let the loop process it. */
-				continue;
-			}
-			/* At this point, we're done with the expression. */
-			if (numstackptr != numstack+1) {
-				/* ... but if there isn't, it's bad */
- err:
-				*perrcode = -1;
-				return *perrcode;
-			}
-			if (numstack->var) {
-				/* expression is $((var)) only, lookup now */
-				errcode = arith_lookup_val(numstack);
-			}
- ret:
-			*perrcode = errcode;
-			return numstack->val;
-		}
-
-		/* Continue processing the expression. */
-		if (arith_isspace(arithval)) {
-			/* Skip whitespace */
-			goto prologue;
-		}
-		p = endofname(expr);
-		if (p != expr) {
-			size_t var_name_size = (p-expr) + 1;  /* trailing zero */
-
-			numstackptr->var = alloca(var_name_size);
-			safe_strncpy(numstackptr->var, expr, var_name_size);
-			expr = p;
- num:
-			numstackptr->contidional_second_val_initialized = 0;
-			numstackptr++;
-			lasttok = TOK_NUM;
-			continue;
-		}
-		if (isdigit(arithval)) {
-			numstackptr->var = NULL;
-#if ENABLE_ASH_MATH_SUPPORT_64
-			numstackptr->val = strtoll(expr, (char **) &expr, 0);
-#else
-			numstackptr->val = strtol(expr, (char **) &expr, 0);
-#endif
-			goto num;
-		}
-		for (p = op_tokens; ; p++) {
-			const char *o;
-
-			if (*p == 0) {
-				/* strange operator not found */
-				goto err;
-			}
-			for (o = expr; *p && *o == *p; p++)
-				o++;
-			if (!*p) {
-				/* found */
-				expr = o - 1;
-				break;
-			}
-			/* skip tail uncompared token */
-			while (*p)
-				p++;
-			/* skip zero delim */
-			p++;
-		}
-		op = p[1];
-
-		/* post grammar: a++ reduce to num */
-		if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC)
-			lasttok = TOK_NUM;
-
-		/* Plus and minus are binary (not unary) _only_ if the last
-		 * token was as number, or a right paren (which pretends to be
-		 * a number, since it evaluates to one). Think about it.
-		 * It makes sense. */
-		if (lasttok != TOK_NUM) {
-			switch (op) {
-			case TOK_ADD:
-				op = TOK_UPLUS;
-				break;
-			case TOK_SUB:
-				op = TOK_UMINUS;
-				break;
-			case TOK_POST_INC:
-				op = TOK_PRE_INC;
-				break;
-			case TOK_POST_DEC:
-				op = TOK_PRE_DEC;
-				break;
-			}
-		}
-		/* We don't want a unary operator to cause recursive descent on the
-		 * stack, because there can be many in a row and it could cause an
-		 * operator to be evaluated before its argument is pushed onto the
-		 * integer stack. */
-		/* But for binary operators, "apply" everything on the operator
-		 * stack until we find an operator with a lesser priority than the
-		 * one we have just extracted. */
-		/* Left paren is given the lowest priority so it will never be
-		 * "applied" in this way.
-		 * if associativity is right and priority eq, applied also skip
-		 */
-		prec = PREC(op);
-		if ((prec > 0 && prec < UNARYPREC) || prec == SPEC_PREC) {
-			/* not left paren or unary */
-			if (lasttok != TOK_NUM) {
-				/* binary op must be preceded by a num */
-				goto err;
-			}
-			while (stackptr != stack) {
-				if (op == TOK_RPAREN) {
-					/* The algorithm employed here is simple: while we don't
-					 * hit an open paren nor the bottom of the stack, pop
-					 * tokens and apply them */
-					if (stackptr[-1] == TOK_LPAREN) {
-						--stackptr;
-						/* Any operator directly after a */
-						lasttok = TOK_NUM;
-						/* close paren should consider itself binary */
-						goto prologue;
-					}
-				} else {
-					operator prev_prec = PREC(stackptr[-1]);
-
-					convert_prec_is_assing(prec);
-					convert_prec_is_assing(prev_prec);
-					if (prev_prec < prec)
-						break;
-					/* check right assoc */
-					if (prev_prec == prec && is_right_associativity(prec))
-						break;
-				}
-				errcode = arith_apply(*--stackptr, numstack, &numstackptr);
-				if (errcode) goto ret;
-			}
-			if (op == TOK_RPAREN) {
-				goto err;
-			}
-		}
-
-		/* Push this operator to the stack and remember it. */
-		*stackptr++ = lasttok = op;
- prologue:
-		++expr;
-	} /* while */
-}
-#endif /* ASH_MATH_SUPPORT */
-
-
 /* ============ main() and helpers */
 
 /*
@@ -13786,7 +13117,7 @@ extern int etext();
 int ash_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int ash_main(int argc UNUSED_PARAM, char **argv)
 {
-	char *shinit;
+	const char *shinit;
 	volatile smallint state;
 	struct jmploc jmploc;
 	struct stackmark smark;
@@ -13799,6 +13130,11 @@ int ash_main(int argc UNUSED_PARAM, char **argv)
 	INIT_G_alias();
 #endif
 	INIT_G_cmdtable();
+#if ENABLE_SH_MATH_SUPPORT
+	math_hooks.lookupvar = lookupvar;
+	math_hooks.setvar = setvar;
+	math_hooks.endofname = endofname;
+#endif
 
 #if PROFILE
 	monitor(4, etext, profile_buf, sizeof(profile_buf), 50);
diff --git a/shell/hush.c b/shell/hush.c
index af67635..e93e5a9 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -76,6 +76,8 @@
 #include <fnmatch.h>
 #endif
 
+#include "math.h"
+
 #define HUSH_VER_STR "0.92"
 
 #if defined SINGLE_APPLET_MAIN
@@ -452,6 +454,9 @@ struct globals {
 #if ENABLE_FEATURE_EDITING
 	line_input_t *line_input_state;
 #endif
+#if ENABLE_SH_MATH_SUPPORT
+	arith_eval_hooks_t hooks;
+#endif
 	pid_t root_pid;
 	pid_t last_bg_pid;
 #if ENABLE_HUSH_JOB
@@ -1164,6 +1169,31 @@ static int unset_local_var(const char *name)
 	return EXIT_SUCCESS;
 }
 
+#if ENABLE_SH_MATH_SUPPORT
+#define is_name(c)      ((c) == '_' || isalpha((unsigned char)(c)))
+#define is_in_name(c)   ((c) == '_' || isalnum((unsigned char)(c)))
+static char *endofname(const char *name)
+{
+	char *p;
+
+	p = (char *) name;
+	if (!is_name(*p))
+		return p;
+	while (*++p) {
+		if (!is_in_name(*p))
+			break;
+	}
+	return p;
+}
+
+static void arith_set_local_var(const char *name, const char *val, int flags)
+{
+	/* arith code doesnt malloc space, so do it for it */
+	char *var = xmalloc(strlen(name) + 1 + strlen(val) + 1);
+	sprintf(var, "%s=%s", name, val);
+	set_local_var(var, flags);
+}
+#endif
 
 /*
  * in_str support
@@ -1374,6 +1404,11 @@ static void o_addstr(o_string *o, const char *str, int len)
 	o->data[o->length] = '\0';
 }
 
+static void o_addstrauto(o_string *o, const char *str)
+{
+	o_addstr(o, str, strlen(str) + 1);
+}
+
 static void o_addstr_duplicate_backslash(o_string *o, const char *str, int len)
 {
 	while (len) {
@@ -1564,7 +1599,7 @@ static int o_glob(o_string *o, int n)
 		char **argv = globdata.gl_pathv;
 		o->length = pattern - o->data; /* "forget" pattern */
 		while (1) {
-			o_addstr(o, *argv, strlen(*argv) + 1);
+			o_addstrauto(o, *argv);
 			n = o_save_ptr_helper(o, n);
 			argv++;
 			if (!*argv)
@@ -1770,6 +1805,28 @@ static int expand_vars_to_list(o_string *output, int n, char *arg, char or_mask)
 			goto store_val;
 		}
 #endif
+#if ENABLE_SH_MATH_SUPPORT
+		case '+': { /* <SPECIAL_VAR_SYMBOL>(cmd<SPECIAL_VAR_SYMBOL> */
+			arith_t res;
+			char buf[30];
+			int errcode;
+			*p = '\0';
+			++arg;
+			debug_printf_subst("ARITH '%s' first_ch %x\n", arg, first_ch);
+			res = arith(arg, &errcode, &G.hooks);
+			if (errcode < 0)
+				switch (errcode) {
+				case -3: maybe_die("arith", "exponent less than 0"); break;
+				case -2: maybe_die("arith", "divide by zero"); break;
+				case -5: maybe_die("arith", "expression recursion loop detected"); break;
+				default: maybe_die("arith", "syntax error");
+				}
+			sprintf(buf, arith_t_fmt, res);
+			o_addstrauto(output, buf);
+			debug_printf_subst("ARITH RES '"arith_t_fmt"'\n", res);
+			break;
+		}
+#endif
 		default: /* <SPECIAL_VAR_SYMBOL>varname<SPECIAL_VAR_SYMBOL> */
 		case_default: {
 			bool exp_len = false, exp_null = false;
@@ -1877,7 +1934,7 @@ static int expand_vars_to_list(o_string *output, int n, char *arg, char or_mask)
 		debug_print_list("expand_vars_to_list[a]", output, n);
 		/* this part is literal, and it was already pre-quoted
 		 * if needed (much earlier), do not use o_addQstr here! */
-		o_addstr(output, arg, strlen(arg) + 1);
+		o_addstrauto(output, arg);
 		debug_print_list("expand_vars_to_list[b]", output, n);
 	} else if (output->length == o_get_last_ptr(output, n) /* expansion is empty */
 	 && !(ored_ch & 0x80) /* and all vars were not quoted. */
@@ -3754,7 +3811,7 @@ static int parse_group(o_string *dest, struct parse_context *ctx,
 	/* command remains "open", available for possible redirects */
 }
 
-#if ENABLE_HUSH_TICK
+#if ENABLE_HUSH_TICK || ENABLE_SH_MATH_SUPPORT
 /* Subroutines for copying $(...) and `...` things */
 static void add_till_backquote(o_string *dest, struct in_str *input);
 /* '...' */
@@ -3834,7 +3891,7 @@ static void add_till_backquote(o_string *dest, struct in_str *input)
  * echo $(echo 'TEST)' BEST)            TEST) BEST
  * echo $(echo \(\(TEST\) BEST)         ((TEST) BEST
  */
-static void add_till_closing_curly_brace(o_string *dest, struct in_str *input)
+static void add_till_closing_paren(o_string *dest, struct in_str *input, bool dbl)
 {
 	int count = 0;
 	while (1) {
@@ -3844,8 +3901,14 @@ static void add_till_closing_curly_brace(o_string *dest, struct in_str *input)
 		if (ch == '(')
 			count++;
 		if (ch == ')')
-			if (--count < 0)
-				break;
+			if (--count < 0) {
+				if (!dbl)
+					break;
+				if (i_peek(input) == ')') {
+					i_getch(input);
+					break;
+				}
+			}
 		o_addchr(dest, ch);
 		if (ch == '\'') {
 			add_till_single_quote(dest, input);
@@ -3866,7 +3929,7 @@ static void add_till_closing_curly_brace(o_string *dest, struct in_str *input)
 		}
 	}
 }
-#endif /* ENABLE_HUSH_TICK */
+#endif /* ENABLE_HUSH_TICK || ENABLE_SH_MATH_SUPPORT */
 
 /* Return code: 0 for OK, 1 for syntax error */
 static int handle_dollar(o_string *dest, struct in_str *input)
@@ -3983,18 +4046,30 @@ static int handle_dollar(o_string *dest, struct in_str *input)
 			o_addchr(dest, SPECIAL_VAR_SYMBOL);
 			break;
 		}
-#if ENABLE_HUSH_TICK
 		case '(': {
-			//int pos = dest->length;
 			i_getch(input);
+
+#if ENABLE_SH_MATH_SUPPORT
+			if (i_peek(input) == '(') {
+				i_getch(input);
+				o_addchr(dest, SPECIAL_VAR_SYMBOL);
+				o_addchr(dest, quote_mask | '+');
+				add_till_closing_paren(dest, input, true);
+				o_addchr(dest, SPECIAL_VAR_SYMBOL);
+				break;
+			}
+#endif
+
+#if ENABLE_HUSH_TICK
+			//int pos = dest->length;
 			o_addchr(dest, SPECIAL_VAR_SYMBOL);
 			o_addchr(dest, quote_mask | '`');
-			add_till_closing_curly_brace(dest, input);
+			add_till_closing_paren(dest, input, false);
 			//debug_printf_subst("SUBST RES2 '%s'\n", dest->data + pos);
 			o_addchr(dest, SPECIAL_VAR_SYMBOL);
+#endif
 			break;
 		}
-#endif
 		case '_':
 			i_getch(input);
 			ch = i_peek(input);
@@ -4526,6 +4601,11 @@ int hush_main(int argc, char **argv)
 #if ENABLE_FEATURE_EDITING
 	G.line_input_state = new_line_input_t(FOR_SHELL);
 #endif
+#if ENABLE_SH_MATH_SUPPORT
+	G.hooks.lookupvar = lookup_param;
+	G.hooks.setvar = arith_set_local_var;
+	G.hooks.endofname = endofname;
+#endif
 	/* XXX what should these be while sourcing /etc/profile? */
 	G.global_argc = argc;
 	G.global_argv = argv;
diff --git a/shell/math.c b/shell/math.c
new file mode 100644
index 0000000..9a46a93
--- /dev/null
+++ b/shell/math.c
@@ -0,0 +1,701 @@
+/*
+ * arithmetic code ripped out of ash shell for code sharing
+ *
+ * Copyright (c) 1989, 1991, 1993, 1994
+ *      The Regents of the University of California.  All rights reserved.
+ *
+ * Copyright (c) 1997-2005 Herbert Xu <herbert@gondor.apana.org.au>
+ * was re-ported from NetBSD and debianized.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Kenneth Almquist.
+ *
+ * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ *
+ * Original BSD copyright notice is retained at the end of this file.
+ */
+/*
+ * rewrite arith.y to micro stack based cryptic algorithm by
+ * Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
+ *
+ * Modified by Paul Mundt <lethal@linux-sh.org> (c) 2004 to support
+ * dynamic variables.
+ *
+ * Modified by Vladimir Oleynik <dzo@simtreas.ru> (c) 2001-2005 to be
+ * used in busybox and size optimizations,
+ * rewrote arith (see notes to this), added locale support,
+ * rewrote dynamic variables.
+ */
+
+#include "busybox.h"
+#include "math.h"
+
+#define a_e_h_t arith_eval_hooks_t
+#define lookupvar (math_hooks->lookupvar)
+#define setvar (math_hooks->setvar)
+#define endofname (math_hooks->endofname)
+
+/* Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
+
+   Permission is hereby granted, free of charge, to any person obtaining
+   a copy of this software and associated documentation files (the
+   "Software"), to deal in the Software without restriction, including
+   without limitation the rights to use, copy, modify, merge, publish,
+   distribute, sublicense, and/or sell copies of the Software, and to
+   permit persons to whom the Software is furnished to do so, subject to
+   the following conditions:
+
+   The above copyright notice and this permission notice shall be
+   included in all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+   IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+   CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+   TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+   SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+/* This is my infix parser/evaluator. It is optimized for size, intended
+ * as a replacement for yacc-based parsers. However, it may well be faster
+ * than a comparable parser written in yacc. The supported operators are
+ * listed in #defines below. Parens, order of operations, and error handling
+ * are supported. This code is thread safe. The exact expression format should
+ * be that which POSIX specifies for shells. */
+
+/* The code uses a simple two-stack algorithm. See
+ * http://www.onthenet.com.au/~grahamis/int2008/week02/lect02.html
+ * for a detailed explanation of the infix-to-postfix algorithm on which
+ * this is based (this code differs in that it applies operators immediately
+ * to the stack instead of adding them to a queue to end up with an
+ * expression). */
+
+/* To use the routine, call it with an expression string and error return
+ * pointer */
+
+/*
+ * Aug 24, 2001              Manuel Novoa III
+ *
+ * Reduced the generated code size by about 30% (i386) and fixed several bugs.
+ *
+ * 1) In arith_apply():
+ *    a) Cached values of *numptr and &(numptr[-1]).
+ *    b) Removed redundant test for zero denominator.
+ *
+ * 2) In arith():
+ *    a) Eliminated redundant code for processing operator tokens by moving
+ *       to a table-based implementation.  Also folded handling of parens
+ *       into the table.
+ *    b) Combined all 3 loops which called arith_apply to reduce generated
+ *       code size at the cost of speed.
+ *
+ * 3) The following expressions were treated as valid by the original code:
+ *       1()  ,    0!  ,    1 ( *3 )   .
+ *    These bugs have been fixed by internally enclosing the expression in
+ *    parens and then checking that all binary ops and right parens are
+ *    preceded by a valid expression (NUM_TOKEN).
+ *
+ * Note: It may be desirable to replace Aaron's test for whitespace with
+ * ctype's isspace() if it is used by another busybox applet or if additional
+ * whitespace chars should be considered.  Look below the "#include"s for a
+ * precompiler test.
+ */
+
+/*
+ * Aug 26, 2001              Manuel Novoa III
+ *
+ * Return 0 for null expressions.  Pointed out by Vladimir Oleynik.
+ *
+ * Merge in Aaron's comments previously posted to the busybox list,
+ * modified slightly to take account of my changes to the code.
+ *
+ */
+
+/*
+ *  (C) 2003 Vladimir Oleynik <dzo@simtreas.ru>
+ *
+ * - allow access to variable,
+ *   used recursive find value indirection (c=2*2; a="c"; $((a+=2)) produce 6)
+ * - realize assign syntax (VAR=expr, +=, *= etc)
+ * - realize exponentiation (** operator)
+ * - realize comma separated - expr, expr
+ * - realise ++expr --expr expr++ expr--
+ * - realise expr ? expr : expr (but, second expr calculate always)
+ * - allow hexadecimal and octal numbers
+ * - was restored loses XOR operator
+ * - remove one goto label, added three ;-)
+ * - protect $((num num)) as true zero expr (Manuel`s error)
+ * - always use special isspace(), see comment from bash ;-)
+ */
+
+#define arith_isspace(arithval) \
+	(arithval == ' ' || arithval == '\n' || arithval == '\t')
+
+typedef unsigned char operator;
+
+/* An operator's token id is a bit of a bitfield. The lower 5 bits are the
+ * precedence, and 3 high bits are an ID unique across operators of that
+ * precedence. The ID portion is so that multiple operators can have the
+ * same precedence, ensuring that the leftmost one is evaluated first.
+ * Consider * and /. */
+
+#define tok_decl(prec,id) (((id)<<5)|(prec))
+#define PREC(op) ((op) & 0x1F)
+
+#define TOK_LPAREN tok_decl(0,0)
+
+#define TOK_COMMA tok_decl(1,0)
+
+#define TOK_ASSIGN tok_decl(2,0)
+#define TOK_AND_ASSIGN tok_decl(2,1)
+#define TOK_OR_ASSIGN tok_decl(2,2)
+#define TOK_XOR_ASSIGN tok_decl(2,3)
+#define TOK_PLUS_ASSIGN tok_decl(2,4)
+#define TOK_MINUS_ASSIGN tok_decl(2,5)
+#define TOK_LSHIFT_ASSIGN tok_decl(2,6)
+#define TOK_RSHIFT_ASSIGN tok_decl(2,7)
+
+#define TOK_MUL_ASSIGN tok_decl(3,0)
+#define TOK_DIV_ASSIGN tok_decl(3,1)
+#define TOK_REM_ASSIGN tok_decl(3,2)
+
+/* all assign is right associativity and precedence eq, but (7+3)<<5 > 256 */
+#define convert_prec_is_assing(prec) do { if (prec == 3) prec = 2; } while (0)
+
+/* conditional is right associativity too */
+#define TOK_CONDITIONAL tok_decl(4,0)
+#define TOK_CONDITIONAL_SEP tok_decl(4,1)
+
+#define TOK_OR tok_decl(5,0)
+
+#define TOK_AND tok_decl(6,0)
+
+#define TOK_BOR tok_decl(7,0)
+
+#define TOK_BXOR tok_decl(8,0)
+
+#define TOK_BAND tok_decl(9,0)
+
+#define TOK_EQ tok_decl(10,0)
+#define TOK_NE tok_decl(10,1)
+
+#define TOK_LT tok_decl(11,0)
+#define TOK_GT tok_decl(11,1)
+#define TOK_GE tok_decl(11,2)
+#define TOK_LE tok_decl(11,3)
+
+#define TOK_LSHIFT tok_decl(12,0)
+#define TOK_RSHIFT tok_decl(12,1)
+
+#define TOK_ADD tok_decl(13,0)
+#define TOK_SUB tok_decl(13,1)
+
+#define TOK_MUL tok_decl(14,0)
+#define TOK_DIV tok_decl(14,1)
+#define TOK_REM tok_decl(14,2)
+
+/* exponent is right associativity */
+#define TOK_EXPONENT tok_decl(15,1)
+
+/* For now unary operators. */
+#define UNARYPREC 16
+#define TOK_BNOT tok_decl(UNARYPREC,0)
+#define TOK_NOT tok_decl(UNARYPREC,1)
+
+#define TOK_UMINUS tok_decl(UNARYPREC+1,0)
+#define TOK_UPLUS tok_decl(UNARYPREC+1,1)
+
+#define PREC_PRE (UNARYPREC+2)
+
+#define TOK_PRE_INC tok_decl(PREC_PRE, 0)
+#define TOK_PRE_DEC tok_decl(PREC_PRE, 1)
+
+#define PREC_POST (UNARYPREC+3)
+
+#define TOK_POST_INC tok_decl(PREC_POST, 0)
+#define TOK_POST_DEC tok_decl(PREC_POST, 1)
+
+#define SPEC_PREC (UNARYPREC+4)
+
+#define TOK_NUM tok_decl(SPEC_PREC, 0)
+#define TOK_RPAREN tok_decl(SPEC_PREC, 1)
+
+#define NUMPTR (*numstackptr)
+
+static int
+tok_have_assign(operator op)
+{
+	operator prec = PREC(op);
+
+	convert_prec_is_assing(prec);
+	return (prec == PREC(TOK_ASSIGN) ||
+			prec == PREC_PRE || prec == PREC_POST);
+}
+
+static int
+is_right_associativity(operator prec)
+{
+	return (prec == PREC(TOK_ASSIGN) || prec == PREC(TOK_EXPONENT)
+	        || prec == PREC(TOK_CONDITIONAL));
+}
+
+typedef struct {
+	arith_t val;
+	arith_t contidional_second_val;
+	char contidional_second_val_initialized;
+	char *var;      /* if NULL then is regular number,
+			   else is variable name */
+} v_n_t;
+
+typedef struct chk_var_recursive_looped_t {
+	const char *var;
+	struct chk_var_recursive_looped_t *next;
+} chk_var_recursive_looped_t;
+
+static chk_var_recursive_looped_t *prev_chk_var_recursive;
+
+static int
+arith_lookup_val(v_n_t *t, a_e_h_t *math_hooks)
+{
+	if (t->var) {
+		const char * p = lookupvar(t->var);
+
+		if (p) {
+			int errcode;
+
+			/* recursive try as expression */
+			chk_var_recursive_looped_t *cur;
+			chk_var_recursive_looped_t cur_save;
+
+			for (cur = prev_chk_var_recursive; cur; cur = cur->next) {
+				if (strcmp(cur->var, t->var) == 0) {
+					/* expression recursion loop detected */
+					return -5;
+				}
+			}
+			/* save current lookuped var name */
+			cur = prev_chk_var_recursive;
+			cur_save.var = t->var;
+			cur_save.next = cur;
+			prev_chk_var_recursive = &cur_save;
+
+			t->val = arith (p, &errcode, math_hooks);
+			/* restore previous ptr after recursiving */
+			prev_chk_var_recursive = cur;
+			return errcode;
+		}
+		/* allow undefined var as 0 */
+		t->val = 0;
+	}
+	return 0;
+}
+
+/* "applying" a token means performing it on the top elements on the integer
+ * stack. For a unary operator it will only change the top element, but a
+ * binary operator will pop two arguments and push a result */
+static int
+arith_apply(operator op, v_n_t *numstack, v_n_t **numstackptr, a_e_h_t *math_hooks)
+{
+	v_n_t *numptr_m1;
+	arith_t numptr_val, rez;
+	int ret_arith_lookup_val;
+
+	/* There is no operator that can work without arguments */
+	if (NUMPTR == numstack) goto err;
+	numptr_m1 = NUMPTR - 1;
+
+	/* check operand is var with noninteger value */
+	ret_arith_lookup_val = arith_lookup_val(numptr_m1, math_hooks);
+	if (ret_arith_lookup_val)
+		return ret_arith_lookup_val;
+
+	rez = numptr_m1->val;
+	if (op == TOK_UMINUS)
+		rez *= -1;
+	else if (op == TOK_NOT)
+		rez = !rez;
+	else if (op == TOK_BNOT)
+		rez = ~rez;
+	else if (op == TOK_POST_INC || op == TOK_PRE_INC)
+		rez++;
+	else if (op == TOK_POST_DEC || op == TOK_PRE_DEC)
+		rez--;
+	else if (op != TOK_UPLUS) {
+		/* Binary operators */
+
+		/* check and binary operators need two arguments */
+		if (numptr_m1 == numstack) goto err;
+
+		/* ... and they pop one */
+		--NUMPTR;
+		numptr_val = rez;
+		if (op == TOK_CONDITIONAL) {
+			if (!numptr_m1->contidional_second_val_initialized) {
+				/* protect $((expr1 ? expr2)) without ": expr" */
+				goto err;
+			}
+			rez = numptr_m1->contidional_second_val;
+		} else if (numptr_m1->contidional_second_val_initialized) {
+			/* protect $((expr1 : expr2)) without "expr ? " */
+			goto err;
+		}
+		numptr_m1 = NUMPTR - 1;
+		if (op != TOK_ASSIGN) {
+			/* check operand is var with noninteger value for not '=' */
+			ret_arith_lookup_val = arith_lookup_val(numptr_m1, math_hooks);
+			if (ret_arith_lookup_val)
+				return ret_arith_lookup_val;
+		}
+		if (op == TOK_CONDITIONAL) {
+			numptr_m1->contidional_second_val = rez;
+		}
+		rez = numptr_m1->val;
+		if (op == TOK_BOR || op == TOK_OR_ASSIGN)
+			rez |= numptr_val;
+		else if (op == TOK_OR)
+			rez = numptr_val || rez;
+		else if (op == TOK_BAND || op == TOK_AND_ASSIGN)
+			rez &= numptr_val;
+		else if (op == TOK_BXOR || op == TOK_XOR_ASSIGN)
+			rez ^= numptr_val;
+		else if (op == TOK_AND)
+			rez = rez && numptr_val;
+		else if (op == TOK_EQ)
+			rez = (rez == numptr_val);
+		else if (op == TOK_NE)
+			rez = (rez != numptr_val);
+		else if (op == TOK_GE)
+			rez = (rez >= numptr_val);
+		else if (op == TOK_RSHIFT || op == TOK_RSHIFT_ASSIGN)
+			rez >>= numptr_val;
+		else if (op == TOK_LSHIFT || op == TOK_LSHIFT_ASSIGN)
+			rez <<= numptr_val;
+		else if (op == TOK_GT)
+			rez = (rez > numptr_val);
+		else if (op == TOK_LT)
+			rez = (rez < numptr_val);
+		else if (op == TOK_LE)
+			rez = (rez <= numptr_val);
+		else if (op == TOK_MUL || op == TOK_MUL_ASSIGN)
+			rez *= numptr_val;
+		else if (op == TOK_ADD || op == TOK_PLUS_ASSIGN)
+			rez += numptr_val;
+		else if (op == TOK_SUB || op == TOK_MINUS_ASSIGN)
+			rez -= numptr_val;
+		else if (op == TOK_ASSIGN || op == TOK_COMMA)
+			rez = numptr_val;
+		else if (op == TOK_CONDITIONAL_SEP) {
+			if (numptr_m1 == numstack) {
+				/* protect $((expr : expr)) without "expr ? " */
+				goto err;
+			}
+			numptr_m1->contidional_second_val_initialized = op;
+			numptr_m1->contidional_second_val = numptr_val;
+		} else if (op == TOK_CONDITIONAL) {
+			rez = rez ?
+				numptr_val : numptr_m1->contidional_second_val;
+		} else if (op == TOK_EXPONENT) {
+			if (numptr_val < 0)
+				return -3;      /* exponent less than 0 */
+			else {
+				arith_t c = 1;
+
+				if (numptr_val)
+					while (numptr_val--)
+						c *= rez;
+				rez = c;
+			}
+		} else if (numptr_val==0)          /* zero divisor check */
+			return -2;
+		else if (op == TOK_DIV || op == TOK_DIV_ASSIGN)
+			rez /= numptr_val;
+		else if (op == TOK_REM || op == TOK_REM_ASSIGN)
+			rez %= numptr_val;
+	}
+	if (tok_have_assign(op)) {
+		char buf[sizeof(arith_t_type)*3 + 2];
+
+		if (numptr_m1->var == NULL) {
+			/* Hmm, 1=2 ? */
+			goto err;
+		}
+		/* save to shell variable */
+		snprintf(buf, sizeof(buf), arith_t_fmt, (arith_t_type) rez);
+		setvar(numptr_m1->var, buf, 0);
+		/* after saving, make previous value for v++ or v-- */
+		if (op == TOK_POST_INC)
+			rez--;
+		else if (op == TOK_POST_DEC)
+			rez++;
+	}
+	numptr_m1->val = rez;
+	/* protect geting var value, is number now */
+	numptr_m1->var = NULL;
+	return 0;
+ err:
+	return -1;
+}
+
+/* longest must be first */
+static const char op_tokens[] ALIGN1 = {
+	'<','<','=',0, TOK_LSHIFT_ASSIGN,
+	'>','>','=',0, TOK_RSHIFT_ASSIGN,
+	'<','<',    0, TOK_LSHIFT,
+	'>','>',    0, TOK_RSHIFT,
+	'|','|',    0, TOK_OR,
+	'&','&',    0, TOK_AND,
+	'!','=',    0, TOK_NE,
+	'<','=',    0, TOK_LE,
+	'>','=',    0, TOK_GE,
+	'=','=',    0, TOK_EQ,
+	'|','=',    0, TOK_OR_ASSIGN,
+	'&','=',    0, TOK_AND_ASSIGN,
+	'*','=',    0, TOK_MUL_ASSIGN,
+	'/','=',    0, TOK_DIV_ASSIGN,
+	'%','=',    0, TOK_REM_ASSIGN,
+	'+','=',    0, TOK_PLUS_ASSIGN,
+	'-','=',    0, TOK_MINUS_ASSIGN,
+	'-','-',    0, TOK_POST_DEC,
+	'^','=',    0, TOK_XOR_ASSIGN,
+	'+','+',    0, TOK_POST_INC,
+	'*','*',    0, TOK_EXPONENT,
+	'!',        0, TOK_NOT,
+	'<',        0, TOK_LT,
+	'>',        0, TOK_GT,
+	'=',        0, TOK_ASSIGN,
+	'|',        0, TOK_BOR,
+	'&',        0, TOK_BAND,
+	'*',        0, TOK_MUL,
+	'/',        0, TOK_DIV,
+	'%',        0, TOK_REM,
+	'+',        0, TOK_ADD,
+	'-',        0, TOK_SUB,
+	'^',        0, TOK_BXOR,
+	/* uniq */
+	'~',        0, TOK_BNOT,
+	',',        0, TOK_COMMA,
+	'?',        0, TOK_CONDITIONAL,
+	':',        0, TOK_CONDITIONAL_SEP,
+	')',        0, TOK_RPAREN,
+	'(',        0, TOK_LPAREN,
+	0
+};
+/* ptr to ")" */
+#define endexpression (&op_tokens[sizeof(op_tokens)-7])
+
+arith_t
+arith(const char *expr, int *perrcode, a_e_h_t *math_hooks)
+{
+	char arithval; /* Current character under analysis */
+	operator lasttok, op;
+	operator prec;
+	operator *stack, *stackptr;
+	const char *p = endexpression;
+	int errcode;
+	v_n_t *numstack, *numstackptr;
+	unsigned datasizes = strlen(expr) + 2;
+
+	/* Stack of integers */
+	/* The proof that there can be no more than strlen(startbuf)/2+1 integers
+	 * in any given correct or incorrect expression is left as an exercise to
+	 * the reader. */
+	numstackptr = numstack = alloca((datasizes / 2) * sizeof(numstack[0]));
+	/* Stack of operator tokens */
+	stackptr = stack = alloca(datasizes * sizeof(stack[0]));
+
+	*stackptr++ = lasttok = TOK_LPAREN;     /* start off with a left paren */
+	*perrcode = errcode = 0;
+
+	while (1) {
+		arithval = *expr;
+		if (arithval == 0) {
+			if (p == endexpression) {
+				/* Null expression. */
+				return 0;
+			}
+
+			/* This is only reached after all tokens have been extracted from the
+			 * input stream. If there are still tokens on the operator stack, they
+			 * are to be applied in order. At the end, there should be a final
+			 * result on the integer stack */
+
+			if (expr != endexpression + 1) {
+				/* If we haven't done so already, */
+				/* append a closing right paren */
+				expr = endexpression;
+				/* and let the loop process it. */
+				continue;
+			}
+			/* At this point, we're done with the expression. */
+			if (numstackptr != numstack+1) {
+				/* ... but if there isn't, it's bad */
+ err:
+				*perrcode = -1;
+				return *perrcode;
+			}
+			if (numstack->var) {
+				/* expression is $((var)) only, lookup now */
+				errcode = arith_lookup_val(numstack, math_hooks);
+			}
+ ret:
+			*perrcode = errcode;
+			return numstack->val;
+		}
+
+		/* Continue processing the expression. */
+		if (arith_isspace(arithval)) {
+			/* Skip whitespace */
+			goto prologue;
+		}
+		p = endofname(expr);
+		if (p != expr) {
+			size_t var_name_size = (p-expr) + 1;  /* trailing zero */
+
+			numstackptr->var = alloca(var_name_size);
+			safe_strncpy(numstackptr->var, expr, var_name_size);
+			expr = p;
+ num:
+			numstackptr->contidional_second_val_initialized = 0;
+			numstackptr++;
+			lasttok = TOK_NUM;
+			continue;
+		}
+		if (isdigit(arithval)) {
+			numstackptr->var = NULL;
+			numstackptr->val = strto_arith_t(expr, (char **) &expr, 0);
+			goto num;
+		}
+		for (p = op_tokens; ; p++) {
+			const char *o;
+
+			if (*p == 0) {
+				/* strange operator not found */
+				goto err;
+			}
+			for (o = expr; *p && *o == *p; p++)
+				o++;
+			if (!*p) {
+				/* found */
+				expr = o - 1;
+				break;
+			}
+			/* skip tail uncompared token */
+			while (*p)
+				p++;
+			/* skip zero delim */
+			p++;
+		}
+		op = p[1];
+
+		/* post grammar: a++ reduce to num */
+		if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC)
+			lasttok = TOK_NUM;
+
+		/* Plus and minus are binary (not unary) _only_ if the last
+		 * token was as number, or a right paren (which pretends to be
+		 * a number, since it evaluates to one). Think about it.
+		 * It makes sense. */
+		if (lasttok != TOK_NUM) {
+			switch (op) {
+			case TOK_ADD:
+				op = TOK_UPLUS;
+				break;
+			case TOK_SUB:
+				op = TOK_UMINUS;
+				break;
+			case TOK_POST_INC:
+				op = TOK_PRE_INC;
+				break;
+			case TOK_POST_DEC:
+				op = TOK_PRE_DEC;
+				break;
+			}
+		}
+		/* We don't want a unary operator to cause recursive descent on the
+		 * stack, because there can be many in a row and it could cause an
+		 * operator to be evaluated before its argument is pushed onto the
+		 * integer stack. */
+		/* But for binary operators, "apply" everything on the operator
+		 * stack until we find an operator with a lesser priority than the
+		 * one we have just extracted. */
+		/* Left paren is given the lowest priority so it will never be
+		 * "applied" in this way.
+		 * if associativity is right and priority eq, applied also skip
+		 */
+		prec = PREC(op);
+		if ((prec > 0 && prec < UNARYPREC) || prec == SPEC_PREC) {
+			/* not left paren or unary */
+			if (lasttok != TOK_NUM) {
+				/* binary op must be preceded by a num */
+				goto err;
+			}
+			while (stackptr != stack) {
+				if (op == TOK_RPAREN) {
+					/* The algorithm employed here is simple: while we don't
+					 * hit an open paren nor the bottom of the stack, pop
+					 * tokens and apply them */
+					if (stackptr[-1] == TOK_LPAREN) {
+						--stackptr;
+						/* Any operator directly after a */
+						lasttok = TOK_NUM;
+						/* close paren should consider itself binary */
+						goto prologue;
+					}
+				} else {
+					operator prev_prec = PREC(stackptr[-1]);
+
+					convert_prec_is_assing(prec);
+					convert_prec_is_assing(prev_prec);
+					if (prev_prec < prec)
+						break;
+					/* check right assoc */
+					if (prev_prec == prec && is_right_associativity(prec))
+						break;
+				}
+				errcode = arith_apply(*--stackptr, numstack, &numstackptr, math_hooks);
+				if (errcode) goto ret;
+			}
+			if (op == TOK_RPAREN) {
+				goto err;
+			}
+		}
+
+		/* Push this operator to the stack and remember it. */
+		*stackptr++ = lasttok = op;
+ prologue:
+		++expr;
+	} /* while */
+}
+
+/*-
+ * Copyright (c) 1989, 1991, 1993, 1994
+ *      The Regents of the University of California.  All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Kenneth Almquist.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
diff --git a/shell/math.h b/shell/math.h
new file mode 100644
index 0000000..a526809
--- /dev/null
+++ b/shell/math.h
@@ -0,0 +1,101 @@
+/* math.h - interface to shell math "library" -- this allows shells to share
+ *          the implementation of arithmetic $((...)) expansions.
+ *
+ * This aims to be a POSIX shell math library as documented here:
+ *	http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04
+ *
+ * See math.c for internal documentation.
+ */
+
+/* The math library has just one function:
+ *
+ *	arith_t arith(const char *expr, int *perrcode, arith_eval_hooks_t *hooks);
+ *
+ *	The first argument is the math string to parse.  All normal expansions must
+ *	be done already.  i.e. no dollar symbols should be present.
+ *
+ *	The second argument is a semi-detailed error description in case something
+ *	goes wrong in the parsing steps.  Currently, those values are (for
+ *	compatibility, you should assume all negative values are errors):
+ *		 0 - no errors (yay!)
+ *		-1 - unspecified problem
+ *		-2 - divide by zero
+ *		-3 - exponent less than 0
+ *		-5 - expression recursion loop detected
+ *
+ *	The third argument is a struct pointer of hooks for your shell (see below).
+ *
+ *	The function returns the answer to the expression.  So if you called it
+ *	with the expression:
+ *		"1 + 2 + 3"
+ *	You would obviously get back 6.
+ */
+
+/* To add support to a shell, you need to implement three functions:
+ *
+ *	lookupvar() - look up and return the value of a variable
+ *
+ *		If the shell does:
+ *			foo=123
+ *		Then the code:
+ *			const char *val = lookupvar("foo");
+ *		Will result in val pointing to "123"
+ *
+ *	setvar() - set a variable to some value
+ *
+ *		If the arithmetic expansion does something like:
+ *			$(( i = 1))
+ *		Then the math code will make a call like so:
+ *			setvar("i", "1", 0);
+ *		The storage for the first two parameters are not allocated, so your
+ *		shell implementation will most likely need to strdup() them to save.
+ *
+ *	endofname() - return the end of a variable name from input
+ *
+ *		The arithmetic code does not know about variable naming conventions.
+ *		So when it is given an experession, it knows something is not numeric,
+ *		but it is up to the shell to dictate what is a valid identifiers.
+ *		So when it encounters something like:
+ *			$(( some_var + 123 ))
+ *		It will make a call like so:
+ *			end = endofname("some_var + 123");
+ *		So the shell needs to scan the input string and return a pointer to the
+ *		first non-identifier string.  In this case, it should return the input
+ *		pointer with an offset pointing to the first space.  The typical
+ *		implementation will return the offset of first char that does not match
+ *		the regex (in C locale): ^[a-zA-Z_][a-zA-Z_0-9]*
+ */
+
+/* To make your life easier when dealing with optional 64bit math support,
+ * rather than assume that the type is "signed long" and you can always
+ * use "%ld" to scan/print the value, use the arith_t helper defines.  See
+ * below for the exact things that are available.
+ */
+
+#ifndef _SHELL_MATH_
+#define _SHELL_MATH_
+
+#if ENABLE_SH_MATH_SUPPORT_64
+typedef int64_t arith_t;
+#define arith_t_type long long
+#define arith_t_fmt "%lld"
+#define strto_arith_t strtoll
+#else
+typedef long arith_t;
+#define arith_t_type long
+#define arith_t_fmt "%ld"
+#define strto_arith_t strtol
+#endif
+
+typedef const char *(*arith_var_lookup_t)(const char *name);
+typedef void (*arith_var_set_t)(const char *name, const char *val, int flags);
+typedef char *(*arith_var_endofname_t)(const char *name);
+typedef struct arith_eval_hooks {
+	arith_var_lookup_t lookupvar;
+	arith_var_set_t setvar;
+	arith_var_endofname_t endofname;
+} arith_eval_hooks_t;
+
+arith_t arith(const char *expr, int *perrcode, arith_eval_hooks_t*);
+
+#endif