Martin Roberts' R2 sequence for dithering in HLSL

mrr2.hlsl

// Martin Roberts' R2 sequence in HLSL
// http://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/
namespace MRR2 {
    float triangularWave(float x) {
        return abs(0.5f - x) * -2.0f + 1.0f;
    }

    static const float  a1 = (0.6180339887498948);
    static const float2 a2 = float2(0.7548776662466927, 0.5698402909980532);
    static const float3 a3 = float3(0.8191725133961644, 0.671043606703789, 0.5497004779019701);
    static const float4 a4 = float4(0.8566748838545029, 0.733891856627126, 0.6287067210378086, 0.53859725722361);

    float computeRawFloatFrom(float  i) { return frac(dot(i, a1)); }
    float computeRawFloatFrom(float2 i) { return frac(dot(i, a2)); }
    float computeRawFloatFrom(float3 i) { return frac(dot(i, a3)); }
    float computeRawFloatFrom(float4 i) { return frac(dot(i, a4)); }

    float computeFloatFrom(float  i) { return triangularWave(computeRawFloatFrom(i)); }
    float computeFloatFrom(float2 i) { return triangularWave(computeRawFloatFrom(i)); }
    float computeFloatFrom(float3 i) { return triangularWave(computeRawFloatFrom(i)); }
    float computeFloatFrom(float4 i) { return triangularWave(computeRawFloatFrom(i)); }
}