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memmove optimization on X86_64
- From: "insight insight" <insight75 at gmail dot com>
- To: libc-alpha at sourceware dot org
- Date: Sun, 6 May 2007 02:52:14 +0200
- Subject: memmove optimization on X86_64
- References: <email@example.com>
i use glibc 2.4 on X86_64 and in debugging a C program, i have looked
at the code of memmove
and I was quite surprise by the code produced. no inline function or
macro and more disturbing
byte by byte copy and not 64 bits by 64 bits copy....
code of the loop of memmove on my computer :
- 0x2b3481a26290 <memmove+144>: movzx eax,BYTE PTR [rbx]
- 0x2b3481a26293 <memmove+147>: add rbx,0x1
- 0x2b3481a26297 <memmove+151>: mov BYTE PTR [rbp],al
- 0x2b3481a2629a <memmove+154>: add rbp,0x1
- 0x2b3481a2629e <memmove+158>: sub rdx,0x1
- 0x2b3481a262a2 <memmove+162>: jne 0x2b3481a26290
memset (or bzero) is much more optimized, because it seems to use
inline function or macro if number of bytes to set is less than a
certain number and else a function with 64 bits sets in memory in the
but these functions should used inline functions in every situations,
the function is else incredibly long to initialize the loop...
i thought that the "rep stosd" was used (in 64 bits, i dont know if
it is "rep stosq", long time i dont use assembler)
Was I juste unlucky with this version of glibc on X86_64 ?