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R_DrawColumnTemplate: minor optimization for non-power-of-2 textures

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This is very likely a platform specific optimization. The
optimization is about a very hot std::clamp. However, the
code is near functionally identical to the libstdc++
implementation, aside from being completely inlined.

I can't say why my version is faster, since I haven't read
any assembly output. More details in source code comments.
This commit is contained in:
James R 2024-01-17 11:30:19 -08:00
parent 3aace4f777
commit 87db195481
1 changed files with 13 additions and 1 deletions
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14
src/r_draw_column.cpp
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@ -263,7 +263,19 @@ static void R_DrawColumnTemplate(drawcolumndata_t *dc)
// -1 is the lower clamp bound because column posts have a "safe" byte before the real data
// and a few bytes after as well
*dest = R_DrawColumnPixel<Type>(dc, dest, std::clamp(frac >> FRACBITS, npow2min, npow2max));
//*dest = R_DrawColumnPixel<Type>(dc, dest, std::clamp(frac >> FRACBITS, npow2min, npow2max));
{
// jartha: faster on my AMD FX-6300 CPU.
// Faster than ternaries, faster than std::min/std::max. Don't ask me why.
// I tested by viewing a non-PO2 texture from a consistent distance so it covered the entire screen.
// The framerate difference was about 50 frames at 640x400.
INT32 n = frac >> FRACBITS;
if (n < npow2min)
n = npow2min;
if (n > npow2max)
n = npow2max;
*dest = R_DrawColumnPixel<Type>(dc, dest, n);
}
dest += vid.width;