Method toColorSpaceUint16FromLinearFloatFast

Engine/Lut.cpp:266–305

the following only works for increasing LUTs

// the following only works for increasing LUTs
unsigned short
Lut::toColorSpaceUint16FromLinearFloatFast(float v) const
{
    assert(init_);
    // algorithm:
    // - convert to 8 bits -> val8u
    // - convert val8u-1, val8u and val8u+1 to float
    // - interpolate linearly in the right interval
    unsigned char v8u = toColorSpaceUint8FromLinearFloatFast(v);
    unsigned char v8u_next, v8u_prev;
    float v32f_next, v32f_prev;
    if (v8u == 0) {
        v8u_prev = 0;
        v8u_next = 1;
        v32f_prev = fromColorSpaceUint8ToLinearFloatFast(0);
        v32f_next = fromColorSpaceUint8ToLinearFloatFast(1);
    } else if (v8u == 255) {
        v8u_prev = 254;
        v8u_next = 255;
        v32f_prev = fromColorSpaceUint8ToLinearFloatFast(254);
        v32f_next = fromColorSpaceUint8ToLinearFloatFast(255);
    } else {
        float v32f = fromColorSpaceUint8ToLinearFloatFast(v8u);
        // we suppose the LUT is an increasing func
        if (v < v32f) {
            v8u_prev = v8u - 1;
            v32f_prev = fromColorSpaceUint8ToLinearFloatFast(v8u_prev);
            v8u_next = v8u;
            v32f_next = v32f;
        } else {
            v8u_prev = v8u;
            v32f_prev = v32f;
            v8u_next = v8u + 1;
            v32f_next = fromColorSpaceUint8ToLinearFloatFast(v8u_next);
        }
    }

    // interpolate linearly
    return (v8u_prev << 8) + v8u_prev + (v - v32f_prev) * ( ( (v8u_next - v8u_prev) << 8 ) + (v8u_next + v8u_prev) ) / (v32f_next - v32f_prev) + 0.5;
}

float
Lut::fromColorSpaceUint16ToLinearFloatFast(unsigned short v) const