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66 行
1.7 KiB
66 行
1.7 KiB
#ifndef UNITY_NOISE_INCLUDED
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#define UNITY_NOISE_INCLUDED
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// A single iteration of Bob Jenkins' One-At-A-Time hashing algorithm.
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uint JenkinsHash(uint x)
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{
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x += (x << 10u);
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x ^= (x >> 6u);
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x += (x << 3u);
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x ^= (x >> 11u);
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x += (x << 15u);
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return x;
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}
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// Compound versions of the hashing algorithm.
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uint JenkinsHash(uint2 v)
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{
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return JenkinsHash(v.x ^ JenkinsHash(v.y));
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}
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uint JenkinsHash(uint3 v)
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{
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return JenkinsHash(v.x ^ JenkinsHash(v.y) ^ JenkinsHash(v.z));
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}
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uint JenkinsHash(uint4 v)
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{
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return JenkinsHash(v.x ^ JenkinsHash(v.y) ^ JenkinsHash(v.z) ^ JenkinsHash(v.w));
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}
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// Construct a float with half-open range [0:1] using low 23 bits.
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// All zeros yields 0, all ones yields the next smallest representable value below 1.
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float ConstructFloat(uint m) {
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const uint ieeeMantissa = 0x007FFFFFu; // Binary FP32 mantissa bitmask
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const uint ieeeOne = 0x3F800000u; // 1.0 in FP32 IEEE
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m &= ieeeMantissa; // Keep only mantissa bits (fractional part)
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m |= ieeeOne; // Add fractional part to 1.0
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float f = asfloat(m); // Range [1:2]
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return f - 1; // Range [0:1]
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}
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// Pseudo-random value in half-open range [0:1]. The distribution is reasonably uniform.
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// Ref: https://stackoverflow.com/a/17479300
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float GenerateHashedRandomFloat(uint x)
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{
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return ConstructFloat(JenkinsHash(x));
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}
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float GenerateHashedRandomFloat(uint2 v)
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{
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return ConstructFloat(JenkinsHash(v));
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}
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float GenerateHashedRandomFloat(uint3 v)
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{
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return ConstructFloat(JenkinsHash(v));
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}
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float GenerateHashedRandomFloat(uint4 v)
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{
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return ConstructFloat(JenkinsHash(v));
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}
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#endif // UNITY_NOISE_INCLUDED
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