diff options
Diffstat (limited to 'shell')
| -rw-r--r-- | shell/math.c | 49 |
1 files changed, 25 insertions, 24 deletions
diff --git a/shell/math.c b/shell/math.c index fbf5c58..0426e2d 100644 --- a/shell/math.c +++ b/shell/math.c @@ -94,7 +94,6 @@ * * 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> @@ -212,18 +211,18 @@ typedef unsigned char operator; #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) +/* TOK_VALUE marks a number, name, name++/name--, or (EXPR): + * IOW: something which can be used as the left side of a binary op. + * Since it's never pushed to opstack, its precedence does not matter. + */ +#define TOK_VALUE tok_decl(PREC_POST, 2) static int is_assign_op(operator op) @@ -625,7 +624,9 @@ evaluate_string(arith_state_t *math_state, const char *expr) var_or_num_t *numstack, *numstackptr; /* Stack of operator tokens */ operator *opstack, *opstackptr; + /* To detect whether we are after a "value": */ operator lasttok; + /* To insert implicit () in ?: ternary op: */ operator insert_op = 0xff; unsigned ternary_level = 0; const char *errmsg; @@ -720,12 +721,12 @@ evaluate_string(arith_state_t *math_state, const char *expr) } else { dbg("[%d] var:IGNORED", (int)(numstackptr - numstack)); expr = p; - numstackptr->var_name = NULL; - numstackptr->val = 0; + numstackptr->var_name = NULL; /* not needed, paranoia */ + numstackptr->val = 0; /* not needed, paranoia */ } - push_num: + push_value: numstackptr++; - lasttok = TOK_NUM; + lasttok = TOK_VALUE; continue; } @@ -747,7 +748,7 @@ evaluate_string(arith_state_t *math_state, const char *expr) */ if (isalnum(*expr) || *expr == '_') goto syntax_err; - goto push_num; + goto push_value; } /* Should be an operator */ @@ -818,15 +819,14 @@ evaluate_string(arith_state_t *math_state, const char *expr) dbg("insert_op=%02x op=%02x", insert_op, op); } tok_found1: - /* post grammar: a++ reduce to num */ - if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC) - lasttok = TOK_NUM; + /* NAME++ is a "value" (something suitable for a binop) */ + if (PREC(lasttok) == PREC_POST) + lasttok = TOK_VALUE; /* Plus and minus are binary (not unary) _only_ if the last - * token was a 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) { + * token was a "value". Think about it. It makes sense. + */ + if (lasttok != TOK_VALUE) { switch (op) { case TOK_ADD: //op = TOK_UPLUS; @@ -857,8 +857,8 @@ evaluate_string(arith_state_t *math_state, const char *expr) prec = PREC(op); if (prec != PREC_LPAREN && prec < UNARYPREC) { /* binary, ternary or RPAREN */ - if (lasttok != TOK_NUM) { - /* must be preceded by a num */ + if (lasttok != TOK_VALUE) { + /* must be preceded by a num (example?) */ goto syntax_err; } /* if op is RPAREN: @@ -883,11 +883,12 @@ evaluate_string(arith_state_t *math_state, const char *expr) operator prev_op = *--opstackptr; if (op == TOK_RPAREN) { if (prev_op == TOK_LPAREN) { - /* Erase var name: (var) is just a number, for example, (var) = 1 is not valid */ + /* Erase var name: for example, (VAR) = 1 is not valid */ numstackptr[-1].var_name = NULL; - /* Any operator directly after a - * close paren should consider itself binary */ - lasttok = TOK_NUM; + /* (EXPR) is a "value": next operator directly after + * close paren should be considered binary + */ + lasttok = TOK_VALUE; goto next; } /* Not (y), but ...x~y). Fall through to evaluate x~y */ |