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[libc] Reduce overall code size by externalising strncmp()

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Typical saving is 20-30 bytes in each file using strncmp().

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2012-11-04 23:53:59 +00:00
parent f8ece72fc9
commit 06766875ad
2 changed files with 40 additions and 21 deletions
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38
src/arch/x86/core/x86_string.c
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@@ -104,3 +104,41 @@ void * __memmove ( void *dest, const void *src, size_t len ) {
return __memcpy_reverse ( dest, src, len );
}
}
/**
* Compare strings (up to a specified length)
*
* @v str1 First string
* @v str2 Second string
* @v len Maximum length
* @ret diff Difference
*/
int strncmp ( const char *str1, const char *str2, size_t len ) {
const void *discard_S;
const void *discard_D;
size_t discard_c;
int diff;
__asm__ __volatile__ ( "\n1:\n\t"
"dec %2\n\t"
"js 2f\n\t"
"lodsb\n\t"
"scasb\n\t"
"jne 3f\n\t"
"testb %b3, %b3\n\t"
"jnz 1b\n\t"
/* Equal */
"\n2:\n\t"
"xor %3, %3\n\t"
"jmp 4f\n\t"
/* Not equal; CF indicates difference */
"\n3:\n\t"
"sbb %3, %3\n\t"
"orb $1, %b3\n\t"
"\n4:\n\t"
: "=&S" ( discard_S ), "=&D" ( discard_D ),
"=&c" ( discard_c ), "=&a" ( diff )
: "0" ( str1 ), "1" ( str2 ), "2" ( len ) );
return diff;
}