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Switch to a < comparison for our calloc check; explain how it works

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Nick Mathewson 2014-11-02 11:42:33 -05:00
parent 81b452d245
commit 0d8abf5365
1 changed files with 7 additions and 3 deletions
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10
src/common/util.c
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@ -195,14 +195,18 @@ tor_malloc_zero_(size_t size DMALLOC_PARAMS)
return result;
}
/* Estimate the square root of SIZE_MAX. */
#define SQRT_SIZE_MAX (((size_t) SIZE_MAX) >> (sizeof(size_t) * 8 / 2))
/* The square root of SIZE_MAX + 1. If a is less than this, and b is less
* than this, then a*b is less than SIZE_MAX. (For example, if size_t is
* 32 bits, then SIZE_MAX is 0xffffffff and this value is 0x10000. If a and
* b are less than this, then their product is at most (65535*65535) ==
* 0xfffe0001. */
#define SQRT_SIZE_MAX_P1 (((size_t)1) << (sizeof(size_t)*4))
/** Return non-zero if and only if the product of the arguments is exact. */
static INLINE int
size_mul_check(const size_t x, const size_t y)
{
return ((x <= SQRT_SIZE_MAX && y <= SQRT_SIZE_MAX) ||
return ((x < SQRT_SIZE_MAX_P1 && y < SQRT_SIZE_MAX_P1) ||
y == 0 || x <= SIZE_MAX / y);
}