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shell/math: decrease stack usage 

function                                             old     new   delta
evaluate_string                                     1412    1467     +55

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
master
Denys Vlasenko 2023-06-17 22:43:46 +02:00
parent 96769486e2
commit 182e5a4d00
1 changed files with 27 additions and 35 deletions
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62
shell/math.c
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@ -579,48 +579,40 @@ static arith_t strto_arith_t(const char *nptr, char **endptr)
# endif
#endif
//TODO: much better estimation than expr_len/2? Such as:
//static unsigned estimate_nums_and_names(const char *expr)
//{
// unsigned count = 0;
// while (*(expr = skip_whitespace(expr)) != '\0') {
// const char *p;
// if (isdigit(*expr)) {
// while (isdigit(*++expr))
// continue;
// count++;
// continue;
// }
// p = endofname(expr);
// if (p != expr) {
// expr = p;
// count++;
// continue;
// }
// }
// return count;
//}
static arith_t
evaluate_string(arith_state_t *math_state, const char *expr)
{
operator lasttok;
const char *errmsg = NULL;
const char *start_expr = expr = skip_whitespace(expr);
unsigned expr_len = strlen(expr) + 2;
/* Stack of integers/names */
/* There can be no more than strlen(startbuf)/2+1
* integers/names in any given correct or incorrect expression.
* (modulo "09v09v09v09v09v" case,
* but we have code to detect that early)
*/
var_or_num_t *const numstack = alloca((expr_len / 2) * sizeof(numstack[0]));
var_or_num_t *numstackptr = numstack;
var_or_num_t *numstack, *numstackptr;
/* Stack of operator tokens */
operator *const opstack = alloca(expr_len * sizeof(opstack[0]));
operator *opstackptr = opstack;
operator *opstack, *opstackptr;
operator lasttok;
operator insert_op = 0xff;
unsigned ternary_level = 0;
const char *errmsg;
const char *start_expr = expr = skip_whitespace(expr);
{
unsigned expr_len = strlen(expr) + 2;
/* If LOTS of whitespace, do not blow up the estimation */
const char *p = expr;
while (*p) {
/* in a run of whitespace, count only 1st char */
if (isspace(*p)) {
while (p++, isspace(*p))
expr_len--;
} else {
p++;
}
}
/* There can be no more than expr_len/2
* integers/names in any given correct or incorrect expression.
* (modulo "09v09v09v09v09v" case,
* but we have code to detect that early)
*/
numstackptr = numstack = alloca((expr_len / 2) * sizeof(numstack[0]));
opstackptr = opstack = alloca(expr_len * sizeof(opstack[0]));
}
/* Start with a left paren */
dbg("(%d) op:TOK_LPAREN", (int)(opstackptr - opstack));