cc9543fed
Denys Vlasenko
2023-07-02
Subject
shell/math: avoid $((3**999999999999999999)) to take years
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Commit Diff GitHub →
shell/math.c+14 -3
| @@ -155,7 +155,7 @@ typedef unsigned char operator; | |
| #define PREC_ASSIGN2 3 | |
| #define TOK_MUL_ASSIGN tok_decl(3,0) | |
| /* "/" and "/=" ops have the same id bits */ | |
| - | #define DIV_ID1 1 |
| + | #define DIV_ID1 1 |
| #define TOK_DIV_ASSIGN tok_decl(3,DIV_ID1) | |
| #define TOK_REM_ASSIGN tok_decl(3,2) | |
| @@ -422,8 +422,19 @@ arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_ | |
| if (right_side_val < 0) | |
| return "exponent less than 0"; | |
| c = 1; | |
| - | while (--right_side_val >= 0) |
| + | while (right_side_val != 0) { |
| + | if ((right_side_val & 1) == 0) { |
| + | /* this if() block is not necessary for correctness, |
| + | * but otherwise echo $((3**999999999999999999)) |
| + | * takes a VERY LONG time |
| + | * (and it's not interruptible by ^C) |
| + | */ |
| + | rez *= rez; |
| + | right_side_val >>= 1; |
| + | } |
| c *= rez; | |
| + | right_side_val--; |
| + | } |
| rez = c; | |
| } | |
| else /*if (op == TOK_DIV || op == TOK_DIV_ASSIGN | |
| @@ -550,7 +561,7 @@ static arith_t parse_with_base(const char *nptr, char **endptr, unsigned base) | |
| /* current char is one of :;<=>[email protected][\]^_`a..z */ | |
| /* in bases up to 36, case does not matter for a-z, | |
| - | * map A..Z and a..z to 10..35: */ |
| + | * map @A..Z and `a..z to 9..35: */ |
| digit = (unsigned)(*nptr | 0x20) - ('a' - 10); | |
| if (base > 36 && *nptr <= '_') { | |
| /* base > 36: A-Z,@,_ are 36-61,62,63 */ | |