diff options
Diffstat (limited to 'shell/math.c')
| -rw-r--r-- | shell/math.c | 35 |
1 files changed, 25 insertions, 10 deletions
diff --git a/shell/math.c b/shell/math.c index 7e2bf5e..4623c97 100644 --- a/shell/math.c +++ b/shell/math.c @@ -133,7 +133,10 @@ typedef unsigned char operator; #define tok_decl(prec,id) (((id)<<5) | (prec)) #define PREC(op) ((op) & 0x1F) +#define PREC_LPAREN 0 #define TOK_LPAREN tok_decl(0,0) +/* Precedence value of RPAREN is used only to distinguish it from LPAREN */ +#define TOK_RPAREN tok_decl(1,1) #define TOK_COMMA tok_decl(1,0) @@ -223,7 +226,6 @@ typedef unsigned char operator; #define SPEC_PREC (UNARYPREC+4) #define TOK_NUM tok_decl(SPEC_PREC, 0) -#define TOK_RPAREN tok_decl(SPEC_PREC, 1) static int is_assign_op(operator op) @@ -789,19 +791,32 @@ evaluate_string(arith_state_t *math_state, const char *expr) * stack until we find an operator with a lesser priority than the * one we have just extracted. If op is right-associative, * then stop "applying" on the equal priority too. - * Left paren is given the lowest priority so it will never be - * "applied" in this way. + * Left paren will never be "applied" in this way. */ prec = PREC(op); - if ((prec > 0 && prec < UNARYPREC) || prec == SPEC_PREC) { - /* not left paren or unary */ + if (prec != PREC_LPAREN && prec < UNARYPREC) { + /* binary, ternary or RPAREN */ if (lasttok != TOK_NUM) { - /* binary op must be preceded by a num */ + /* must be preceded by a num */ goto err; } - /* 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 op is RPAREN: + * while opstack is not empty: + * pop prev_op + * if prev_op is LPAREN (finished evaluating (EXPR)): + * goto N + * evaluate prev_op on top of numstack + * BUG (unpaired RPAREN) + * else (op is not RPAREN): + * while opstack is not empty: + * pop prev_op + * if can't evaluate prev_op (it is lower precedence than op): + * push prev_op back + * goto P + * evaluate prev_op on top of numstack + * P: push op + * N: loop to parse the rest of string + */ while (opstackptr != opstack) { operator prev_op = *--opstackptr; if (op == TOK_RPAREN) { @@ -821,7 +836,7 @@ evaluate_string(arith_state_t *math_state, const char *expr) if (prev_prec < prec || (prev_prec == prec && is_right_associative(prec)) ) { - /* ...x~y@: push @ on opstack */ + /* ...x~y@. push @ on opstack */ opstackptr++; /* undo removal of ~ op */ goto push_op; } |