Re: No difference on my machine

Evenbit wrote:
Comparing 'xor eax, eax' with 'mov eax, 0' from the CLAX thread:

; nasm -f elf -o timeit.o timeit.asm
; gcc -s -o timeit timeit.o

extern exit
extern printf

global main

section .data

tvsec dd 0
tvusec dd 0
tz1 dd 1
tz2 dd 0
secs db "Sec: %i", 10, 0
store dd 0

section .text

main:

mov eax, 78 ; gettimeofday
mov ebx, tvsec
mov edx, tz1
int 0x80

mov eax, DWORD [tvsec]
mov DWORD [store], eax

mov ecx, 2
mainloop:
mov edx, -1
subloop:
xor eax, eax ; exchange with 'mov eax, 0'
dec edx
jnz subloop

dec ecx
jnz mainloop

mov eax, 78
mov ebx, tvsec
mov edx, tz1
int 0x80

mov eax, DWORD [tvsec]
sub eax, DWORD [store]

push eax
push secs
call printf

push 0
call exit

Good one, Nathan! No difference on my P4, that I can notice. Replacing "dec" with "sub" gives a big speedup, though...

Don't you want "tz" in ecx, not edx?

Best,
Frank


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