Author: Wylie Garvin
Date: 01:40:13 02/03/02
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On February 01, 2002 at 06:05:22, Steve Maughan wrote: >Ed, > >>It will be even slightly stronger because surprise surprise the Windows version >>runs 11-12% faster than the DOS version due to the use of a new compiler. > >I thought Rebel's engine was 100% assembler, in which case the compiler would >make little or no difference to the execution speed. What am I missing? > >Regards, > >Steve This is not surprising since Pentiums and up are primarily designed to execute 32-bit code (i.e. in a 32-bit code segment). When running DOS code under Windows you are running in v86 mode from a 16-bit code segment, so the processor does some things slower. If you use 32-bit instructions, then in certain cases (e.g. instructions with immediates, I think) this will slow things down some more. Hey Ed, I found a web page today that I somehow never noticed before. It contains some of the most detailed information I've seen to date about optimizing for all kinds of Pentiums (PPlain thru PIII; P4 not included). I only noticed one thing in it which *might* be incorrect, and more likely it is me who is incorrect. :) http://www.agner.org/assem/pentopt.zip cheers, wylie The thing I noticed was, it claims that on PPro/P2/P3 the xor reg,reg and sub reg,reg patterns do NOT break dependency chains, while mov reg,0 does. The intel documentation for P2/P3 does explicitly claim that xor reg,reg breaks dependency chains. On P4 it most certainly does, along with sub reg,reg and pxor mm,mm. Anyways.
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