Just saw this beauty from some example code:

DXT3AlphaBlock compressDXT3Alpha(vec4 colors[16])
{
	DXT3AlphaBlock dxt3Alpha;

	unsigned int quantizedAlpha0 = quantize4(int(colors[0].w * 255.0 + .5));
	unsigned int quantizedAlpha1 = quantize4(int(colors[1].w * 255.0 + .5));
	unsigned int quantizedAlpha2 = quantize4(int(colors[2].w * 255.0 + .5));
	unsigned int quantizedAlpha3 = quantize4(int(colors[3].w * 255.0 + .5));
	unsigned int quantizedAlpha4 = quantize4(int(colors[4].w * 255.0 + .5));
	unsigned int quantizedAlpha5 = quantize4(int(colors[5].w * 255.0 + .5));
	unsigned int quantizedAlpha6 = quantize4(int(colors[6].w * 255.0 + .5));
	unsigned int quantizedAlpha7 = quantize4(int(colors[7].w * 255.0 + .5));
	dxt3Alpha.alphas[0] =
		quantizedAlpha0 << unsigned int(0) |
		quantizedAlpha1 << unsigned int(4) |
		quantizedAlpha2 << unsigned int(8) |
		quantizedAlpha3 << unsigned int(12) |
		quantizedAlpha4 << unsigned int(16) |
		quantizedAlpha5 << unsigned int(20) |
		quantizedAlpha6 << unsigned int(24) |
		quantizedAlpha7 << unsigned int(28);
	
	unsigned int quantizedAlpha8 = quantize4(int(colors[8].w * 255.0 + .5));
	unsigned int quantizedAlpha9 = quantize4(int(colors[9].w * 255.0 + .5));
	unsigned int quantizedAlpha10 = quantize4(int(colors[10].w * 255.0 + .5));
	unsigned int quantizedAlpha11 = quantize4(int(colors[11].w * 255.0 + .5));
	unsigned int quantizedAlpha12 = quantize4(int(colors[12].w * 255.0 + .5));
	unsigned int quantizedAlpha13 = quantize4(int(colors[13].w * 255.0 + .5));
	unsigned int quantizedAlpha14 = quantize4(int(colors[14].w * 255.0 + .5));
	unsigned int quantizedAlpha15 = quantize4(int(colors[15].w * 255.0 + .5));
	dxt3Alpha.alphas[1] =
		quantizedAlpha8 << unsigned int(0) |
		quantizedAlpha9 << unsigned int(4) |
		quantizedAlpha10 << unsigned int(8) |
		quantizedAlpha11 << unsigned int(12) |
		quantizedAlpha12 << unsigned int(16) |
		quantizedAlpha13 << unsigned int(20) |
		quantizedAlpha14 << unsigned int(24) |
		quantizedAlpha15 << unsigned int(28);
	
	return dxt3Alpha;
}

What do you think?

-MIGI0027

Who ever coded that doesn't know what "funroll-all-loops" is :P and tried to achieve same result by hand.

Almost looks like ASCII art - is that a Death Star turret gun?

Hah! Never saw that coming, but now when I look at it...

Could be code generated by a tool, although it would be unusual to see that in sample code.

Hasn't really been all that many years since hand unrolling was a common practice. Still, it is pretty unusual to see it nowadays.

I actually find that the original version is more easily understood than doing it with loops

DXT3AlphaBlock compressDXT3Alpha(vec4 colors[16])
{
	DXT3AlphaBlock dxt3Alpha;

	for( int j=0; j!=2; ++j )
	{
		unsigned int result = 0;
		for( int i=7; i>=0; --i )
		{
			unsigned int quantized = quantize4(int(colors[i+j*8].w * 255.0 + .5));
			result = result<<2 | quantized;
		}
		dxt3Alpha.alphas[j] = result;
	}

	return dxt3Alpha;
}

Amateur. I've once dealt with code written... I think in Korea. The variables were numbered up to... like 74, in a convenient 800 LOC function.