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Spu2-x: Fix noise generator. (#3030) 

Fixes the noise generator outputting a 4.8 kHz tone instead of white noise. The random number generator used in GetNoiseValues currently repeats every 10 samples, which is really really awful for a random number generator.

New code based on http://problemkaputt.de/psx-spx.htm#spunoisegenerator
This commit is contained in:
monster860 2019-07-22 12:46:10 -04:00 committed by lightningterror
parent 7d1d88e408
commit 902b88ac1a
1 changed files with 4 additions and 14 deletions
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18
plugins/spu2-x/src/Mixer.cpp
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@ -257,22 +257,12 @@ static __forceinline void GetNextDataDummy(V_Core &thiscore, uint voiceidx)
static s32 __forceinline GetNoiseValues()
{
static s32 Seed = 0x41595321;
s32 retval = 0x8000;
static u16 lfsr = 0xC0FEu;
if (Seed & 0x100)
retval = (Seed & 0xff) << 8;
else if (Seed & 0xffff)
retval = 0x7fff;
u16 bit = lfsr ^ (lfsr << 3) ^ (lfsr << 4) ^ (lfsr << 5);
lfsr = (lfsr << 1) | (bit >> 15);
s32 x = _rotr(Seed, 0x5);
x ^= 0x9a;
s32 y = _rotl(x, 0x2);
y += x;
y ^= x;
Seed = _rotr(y, 0x3);
return retval;
return (s16)lfsr;
}
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