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I made my own DOS implementation (Announce)

posted by Rugxulo Homepage, Usono, 28.03.2024, 01:29

> My previous message did not make much sense. It turns out that MMX does
> only 32-bit math and many sources from the internet are wrong about this. I
> replaced the MMX routines with code that uses the 32-bit i386 registers.
> The new code is also much faster.
Keep in mind that MMX is still using the FPU behind the scenes.

> I also tried SSE2 instructions, but interestingly they were not much faster
> than MMX either.
You're using a 3 Ghz Pentium 4? Very quirky machines. SSE2 was first introduced with the Pentium 4, and is probably preferred for that machine (and default for AMD64). If it's not "faster" on that one machine, keep in mind that Pentium 4 had long pipelines and had no barrel shifter (i.e. shifts are slow) and other quirky things (use add 1 instead of inc). Even SSE2's bandwidth would greatly increase in later cpus, so it's definitely faster nowadays. GCC always had surprisingly good tuning for Pentium 4. Feel free to compare its output. Oh, and FXSAVE/FXRSTOR is faster than the old FPU way of saving things.

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