a16509892
Denys Vlasenko
2023-06-19
Subject
shell/math: fix comments about jammed-together num+num corner cases
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shell/math.c+16 -8
| @@ -613,7 +613,7 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| const char *start_expr = expr = skip_whitespace(expr); | |
| { | |
| - | unsigned expr_len = strlen(expr) + 2; |
| + | unsigned expr_len = strlen(expr); |
| /* If LOTS of whitespace, do not blow up the estimation */ | |
| const char *p = expr; | |
| while (*p) { | |
| @@ -625,14 +625,21 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| p++; | |
| } | |
| } | |
| - | /* There can be no more than expr_len/2 |
| + | dbg("expr:'%s' expr_len:%u", expr, expr_len); |
| + | /* expr_len deep opstack is needed. Think "------------7". |
| + | * Only "?" operator temporarily needs two opstack slots |
| + | * (IOW: more than one slot), but its second slot (LPAREN) |
| + | * is popped off when ":" is reached. |
| + | */ |
| + | opstackptr = opstack = alloca(expr_len * sizeof(opstack[0])); |
| + | /* There can be no more than (expr_len/2 + 1) |
| * integers/names in any given correct or incorrect expression. | |
| - | * (modulo "09v09v09v09v09v" case, |
| + | * (modulo "09", "0v" cases where 2 chars are 2 ints/names, |
| * but we have code to detect that early) | |
| */ | |
| - | dbg("expr:'%s' expr_len:%u", expr, expr_len); |
| - | numstackptr = numstack = alloca((expr_len / 2) * sizeof(numstack[0])); |
| - | opstackptr = opstack = alloca(expr_len * sizeof(opstack[0])); |
| + | expr_len = (expr_len / 2) |
| + | + 1 /* "1+2" has two nums, 2 = len/2+1, NOT len/2 */; |
| + | numstackptr = numstack = alloca(expr_len * sizeof(numstack[0])); |
| } | |
| /* Start with a left paren */ | |
| @@ -714,8 +721,9 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| dbg("[%d] val:%lld", (int)(numstackptr - numstack), numstackptr->val); | |
| /* A number can't be followed by another number, or a variable name. | |
| * We'd catch this later anyway, but this would require numstack[] | |
| - | * to be twice as deep to handle strings where _every_ char is |
| - | * a new number or name. Example: 09v09v09v09v09v09v09v09v09v |
| + | * to be ~twice as deep to handle strings where _every_ char is |
| + | * a new number or name. |
| + | * Examples: "09" is two numbers, "0v" is number and name. |
| */ | |
| if (isalnum(*expr) || *expr == '_') | |
| goto syntax_err; | |