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SimpleRandmizer: Fix certain bits generated by getRandomBytes are always 0 

This is because in Linux RAND_MAX is 2**31-1 and we used int32_t to
hold random number from random() and got each bytes. This means that
highest bit is always unset. In little endian system, every 4n-th (n
>=0) byte has highest bit is unset. To fix this, we just use lower 2
bytes of random().
pull/135/merge
Tatsuhiro Tsujikawa 2013-09-26 00:41:33 +09:00
parent ac996737e5
commit 7f18494a8c
1 changed files with 5 additions and 4 deletions
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9
src/SimpleRandomizer.cc
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@ -123,11 +123,12 @@ void SimpleRandomizer::getRandomBytes(unsigned char *buf, size_t len)
} }
#else #else
while (len) { while (len) {
// If RAND_MAX is less than 2**16-1, we are in trouble.
union { union {
int32_t r; uint16_t r;
uint8_t b[4]; uint8_t b[2];
} r = { (int32_t)random() }; } r = { (uint16_t)(random() & 0xffffu) };
for (auto i = 0; i < 4 && len; ++i, --len) { for (auto i = 0; i < 2 && len; ++i, --len) {
*buf++ = r.b[i]; *buf++ = r.b[i];
} }
} }