diff options
| -rw-r--r-- | miscutils/bc.c | 21 |
1 files changed, 11 insertions, 10 deletions
diff --git a/miscutils/bc.c b/miscutils/bc.c index 7be2d0b..876244b 100644 --- a/miscutils/bc.c +++ b/miscutils/bc.c @@ -1442,20 +1442,21 @@ static void bc_num_copy(BcNum *d, BcNum *s) static BC_STATUS zbc_num_ulong(BcNum *n, unsigned long *result_p) { size_t i; - unsigned long pow, result; + unsigned long result; if (n->neg) RETURN_STATUS(bc_error("negative number")); - for (result = 0, pow = 1, i = n->rdx; i < n->len; ++i) { - unsigned long prev = result, powprev = pow; - - result += ((unsigned long) n->num[i]) * pow; - pow *= 10; - - if (result < prev || pow < powprev) + result = 0; + i = n->len; + while (i > n->rdx) { + unsigned long prev = result; + result = result * 10 + n->num[--i]; + // Even overflowed N*10 can still satisfy N*10>=N. For example, + // 0x1ff00000 * 10 is 0x13f600000, + // or 0x3f600000 truncated to 32 bits. Which is larger. + // However, (N*10)/8 < N check is always correct. + if ((result / 8) < prev) RETURN_STATUS(bc_error("overflow")); - prev = result; - powprev = pow; } *result_p = result; |