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2.2 KiB

#ifndef UNITY_RANDOM_INCLUDED
#define UNITY_RANDOM_INCLUDED
#if !defined(SHADER_API_GLES)
// A single iteration of Bob Jenkins' One-At-A-Time hashing algorithm.
uint JenkinsHash(uint x)
{
x += (x << 10u);
x ^= (x >> 6u);
x += (x << 3u);
x ^= (x >> 11u);
x += (x << 15u);
return x;
}
// Compound versions of the hashing algorithm.
uint JenkinsHash(uint2 v)
{
return JenkinsHash(v.x ^ JenkinsHash(v.y));
}
uint JenkinsHash(uint3 v)
{
return JenkinsHash(v.x ^ JenkinsHash(v.y) ^ JenkinsHash(v.z));
}
uint JenkinsHash(uint4 v)
{
return JenkinsHash(v.x ^ JenkinsHash(v.y) ^ JenkinsHash(v.z) ^ JenkinsHash(v.w));
}
// Construct a float with half-open range [0, 1) using low 23 bits.
// All zeros yields 0, all ones yields the next smallest representable value below 1.
float ConstructFloat(int m) {
const int ieeeMantissa = 0x007FFFFF; // Binary FP32 mantissa bitmask
const int ieeeOne = 0x3F800000; // 1.0 in FP32 IEEE
m &= ieeeMantissa; // Keep only mantissa bits (fractional part)
m |= ieeeOne; // Add fractional part to 1.0
float f = asfloat(m); // Range [1, 2)
return f - 1; // Range [0, 1)
}
float ConstructFloat(uint m)
{
return ConstructFloat(asint(m));
}
// Pseudo-random value in half-open range [0, 1). The distribution is reasonably uniform.
// Ref: https://stackoverflow.com/a/17479300
float GenerateHashedRandomFloat(uint x)
{
return ConstructFloat(JenkinsHash(x));
}
float GenerateHashedRandomFloat(uint2 v)
{
return ConstructFloat(JenkinsHash(v));
}
float GenerateHashedRandomFloat(uint3 v)
{
return ConstructFloat(JenkinsHash(v));
}
float GenerateHashedRandomFloat(uint4 v)
{
return ConstructFloat(JenkinsHash(v));
}
float Hash(uint s)
{
s = s ^ 2747636419u;
s = s * 2654435769u;
s = s ^ (s >> 16);
s = s * 2654435769u;
s = s ^ (s >> 16);
s = s * 2654435769u;
return float(s) * rcp(4294967296.0); // 2^-32
}
float2 InitRandom(float2 input)
{
float2 r;
r.x = Hash(uint(input.x * UINT_MAX));
r.y = Hash(uint(input.y * UINT_MAX));
return r;
}
#endif // SHADER_API_GLES
#endif // UNITY_RANDOM_INCLUDED