Bad idea: build a captcha library that embeds DOSBox so it can make you beat levels/puzzles from DOS games to continue.
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oh sweet laser jesus I found the upload palette function and THEY UNROLLED IT
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why do:
for(int i=0;i<256;i++){
upload_color(i,palette[i]);
}when you can do
upload_color(0,palette[0]);
upload_color(1,palette[1]);
upload_color(2,palette[2]);
upload_color(3,palette[3]);
upload_color(4,palette[4]);
upload_color(5,palette[5]);and just repeat 251 more times
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the worst part is that this was done with a compiler from 1991 so there's no way it unrolled the loop itself. they did this manually
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@foone Any idea why? I have extremely little experience with programming in that era, but I remember that code size was always a serious concern ... so unrolling it sounds like a bad idea, unless they really needed it for performance.
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@saua it runs slightly faster. like a couple cycles per "iteration".
This is aiming at CPUs so slow that that might matter
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No compiler flags that would do this?
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oh that's cute. their set_palette function takes two arguments: a pointer to the palette, and a number of extra palettes to apply.
so they could set up an array of palettes in decreasing brightness, and just do set_palette(&fade_pallets[0], 64) to go through them.
but the same function is a regular one-time set_palette if you just pass 1 for the second argument.
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@simonzerafa in 1991? I don't think so. Not a for loop this big.
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"hey ghidra what calls set_palette?"
"I don't know! you're in 16bit segmented mode! pointers are MEANINGLESS
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ahh, nope! I misidentified it.
the second parameter on set_palette is how many frames to set it for.
The same palette gets set.it vsyncs every time so this is a set_palette that's also a timing function
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@foone the only thing better than __FILE__ is __func__
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or maybe not? it's too 2am to tell.
ANYWAY I'm currently debugging through a function that's 256 palette entry uploads and my debugger has no "run until return" function so I have to manually hit next instruction SO MANY TIMES
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(approximately 1536 times)
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this set_palette code got loaded into the segment 0BBC, one of the only 16-bit DOS segments marked red in shinigami eyes
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@[email protected] maybe they wanted to experience the joys of funroll-loops all by themselves
not much else going on in 91 -
Foone🏳️⚧️replied to Foone🏳️⚧️ last edited by [email protected]
interesting: the same function is called to fade a palette TO black and to fade a palette FROM black
I wonder if it's specialized to just be palette to black and vice versa, or if it does arbitrary fades between two palettes?
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@aud good point, it was a famously uneventful year
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I'm staring at this code going "if it was less 2am, I could understand this math"
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this math:
local_8 = (int)(0x3f / (long)param_1) + 1;
iVar6 = 0;
do {
uVar7 = (undefined2)((ulong)param_2 >> 0x10);
uVar8 = (undefined2)((ulong)param_4 >> 0x10);
iVar4 = (int)param_4;
uVar1 = (int)*(char *)(iVar4 + iVar6) - (int)*(char *)((int)param_2 + iVar6);
uVar2 = (int)uVar1 >> 0xf;
local_608[iVar6] = (char)((int)((uVar1 ^ uVar2) - uVar2) / local_8) + '\x01';
iVar6 = iVar6 + 1;
} while (iVar6 < 0x300); -
@foone Loop unrolling is older than that though. Although maybe not on these platforms, unless they were cross compiling?
It's in the "dragon book" on compiler design in the 70's. And by the 80's, in the workstation space, that and other techniques were common (my ex-wife worked on compiler optimization back then).
