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feat: add fast random float gen based on pcg #1158

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Merged
alandtse merged 2 commits into from
Jun 18, 2025
Merged

feat: add fast random float gen based on pcg #1158

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f94bc88
feat: add fast random float gen based on pcg
sicsix Jun 17, 2025
fcb0d0e
small tidy, clearer variable names
sicsix Jun 17, 2025
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65 changes: 62 additions & 3 deletions package/Shaders/Common/Random.hlsli
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Original file line number Diff line number Diff line change
Expand Up @@ -102,10 +102,11 @@ namespace Random
return fmix(h);
}

uint pcg(uint v)
uint pcg(inout uint state)
{
uint state = v * 747796405u + 2891336453u;
uint word = ((state >> ((state >> 28u) + 4u)) ^ state) * 277803737u;
uint prevState = state;
state = state * 747796405u + 2891336453u;
uint word = ((prevState >> ((prevState >> 28u) + 4u)) ^ prevState) * 277803737u;
return (word >> 22u) ^ word;
}

Expand Down Expand Up @@ -151,6 +152,64 @@ namespace Random
return n;
}

float f1(inout uint state, out uint randBits)
{
randBits = pcg(state);
uint bits = randBits & 0x007FFFFFu | 0x3F800000u;
return asfloat(bits) - 1.0f;
}

float f1(inout uint state)
{
uint randBits;
return f1(state, randBits);
}

float2 f2(inout uint state, out uint randBits)
{
randBits = pcg(state);
uint bits0 = randBits & 0x007FFFFFu | 0x3F800000u;
uint bits1 = randBits >> 9 | 0x3F800000u;
return float2(asfloat(bits0), asfloat(bits1)) - 1.0f;
}

float2 f2(inout uint state)
{
uint randBits;
return f2(state, randBits);
}

float3 f3(inout uint state, out uint randBits)
{
randBits = pcg(state);
uint bits0 = randBits & 0x007FFFFFu | 0x3F800000u;
uint bits1 = (randBits << 22 | randBits >> 10) & 0x007FFFFFu | 0x3F800000u;
uint bits2 = (randBits << 11 | randBits >> 21) & 0x007FFFFFu | 0x3F800000u;
return float3(asfloat(bits0), asfloat(bits1), asfloat(bits2)) - 1.0f;
}

float3 f3(inout uint state)
{
uint randBits;
return f3(state, randBits);
}

float4 f4(inout uint state, out uint randBits)
{
randBits = pcg(state);
uint bits0 = randBits & 0x007FFFFFu | 0x3F800000u;
uint bits1 = (randBits << 24 | randBits >> 8) & 0x007FFFFFu | 0x3F800000u;
uint bits2 = (randBits << 16 | randBits >> 16) & 0x007FFFFFu | 0x3F800000u;
uint bits3 = (randBits << 8 | randBits >> 24) & 0x007FFFFFu | 0x3F800000u;
return float4(asfloat(bits0), asfloat(bits1), asfloat(bits2), asfloat(bits3)) - 1.0f;
}

float4 f4(inout uint state)
{
uint randBits;
return f4(state, randBits);
}

///////////////////////////////////////////////////////////
// BLUE-LIKE HASHES / LOW DISCREPANCY SEQUENCES
///////////////////////////////////////////////////////////
Expand Down