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[libc] Rewrite string functions

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Some of the C library string functions have an unknown provenance.
Reimplement all such functions to avoid potential licensing
uncertainty.

Remove the inline-assembler versions of strlen(), memswap(), and
strncmp(); these save a minimal amount of space (around 40 bytes in
total) and are not performance-critical.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2015-02-16 17:59:11 +00:00
parent b54167b8b6
commit 8ee39f7432
6 changed files with 400 additions and 432 deletions
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84
src/arch/x86/core/x86_string.c
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@@ -104,87 +104,3 @@ void * __memmove ( void *dest, const void *src, size_t len ) {
return __memcpy_reverse ( dest, src, len );
}
}
/**
* Swap memory areas
*
* @v dest Destination address
* @v src Source address
* @v len Length
* @ret dest Destination address
*/
void * memswap ( void *dest, void *src, size_t len ) {
size_t discard_c;
int discard;
__asm__ __volatile__ ( "\n1:\n\t"
"dec %2\n\t"
"js 2f\n\t"
"movb (%0,%2), %b3\n\t"
"xchgb (%1,%2), %b3\n\t"
"movb %b3, (%0,%2)\n\t"
"jmp 1b\n\t"
"2:\n\t"
: "=r" ( src ), "=r" ( dest ),
"=&c" ( discard_c ), "=&q" ( discard )
: "0" ( src ), "1" ( dest ), "2" ( len )
: "memory" );
return dest;
}
/**
* Calculate length of string
*
* @v string String
* @ret len Length (excluding NUL)
*/
size_t strlen ( const char *string ) {
const char *discard_D;
size_t len_plus_one;
__asm__ __volatile__ ( "repne scasb\n\t"
"not %1\n\t"
: "=&D" ( discard_D ), "=&c" ( len_plus_one )
: "0" ( string ), "1" ( -1UL ), "a" ( 0 ) );
return ( len_plus_one - 1 );
}
/**
* 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;
}