As a little exercise in SSE2 programming I wrote a little random number
generator based on a linear feedback shift register of 62 bit length.
It is a bit slower than the standard library rand-function and useless
for cryptographical uses, but it has a much larger sequence of random
The sequence repeats at 4.61169E+18 numbers.
Here it is the code - in case someone ever needs such a thing. It’s
written for MSVC.
static __m128i LFSR;
void InitRandom (int Seed)
LFSR = _mm_cvtsi32_si128 (Seed);
int GetRandom (int NumBits)
__m128i seed = LFSR;
__m128i one = _mm_cvtsi32_si128(1);
for (i=0; i<NumBits; i++)
// generate xor of adjecting bits
__m128i temp = _mm_xor_si128(seed, _mm_srli_epi64(seed,1));
// generate xor of feedback bits 5,6 and 62,61
__m128i NewBit = _mm_xor_si128( _mm_srli_epi64(temp,5),
// Mask out single bit:
NewBit = _mm_and_si128 (NewBit, one);
// Shift & insert new result bit:
seed = _mm_or_si128 (NewBit, _mm_add_epi64 (seed,seed));
// Write back seed...
LFSR = seed;
// generate mask of NumBit ones.
mask = _mm_srli_epi64 (_mm_cmpeq_epi8(seed, seed), 64-NumBits);
// return random number:
return _mm_cvtsi128_si32 (_mm_and_si128(seed,mask));
Please log in or register to post a reply.