gistfile1.cpp

//setup
x = startX;
y = startY;
float sX = s1*x; //s1 is 'a' for s
float sY = s2*y; //s2 is 'b' for s
float wX = w1*X; //w1 is 'a' for w
float wY = w2*Y; //w2 is 'b' for w
//optimized loop:
for(; y < yEnd; ++y){
    for(; x < xEnd; ++x){
        float sOverW = sX + sY + s3; //s3 is 'c' for s
        float finalW = 1.0f / (wX + wY + w3); //w3 is 'c' for w
        float finalS = sOverW * finalW;
        sX += s1;
        wX += w1;
    }
    sY += s2;
    wY += w2;
}