Implementation of some string.h function using SSE2 instructions
Paweł Sikora
pluto@agmk.net
Wed Aug 8 11:27:00 GMT 2007
Wojciech MuÂła pisze:
> Hi all,
>
> I just subscribed to the list.
>
> Does anybody work on SSE2 implementation?
Hi,
few days ago i've started implementation of strcmp()
for aligned data using <emmintrin.h> builtins.
gcc42/43 optimizes such code pretty well
and raw asm. implementation isn't required.
$ cat sse2_strings.h
#ifndef sse2_strings_h
#define sse2_strings_h
typedef char __attribute__(( aligned( 16 ) )) sse2_aligned_byte;
typedef sse2_aligned_byte const* sse2_byte_buffer;
int sse2_strcmp( sse2_byte_buffer s1, sse2_byte_buffer s2 );
#endif
$ cat sse2_strings.c
#include "sse2_strings.h"
#include <emmintrin.h>
static inline __m128i not( __m128i x )
{
__m128i zero = { 0 };
__m128i ones = _mm_cmpeq_epi8( zero, zero );
return _mm_xor_si128( x, ones );
}
int sse2_strcmp( sse2_byte_buffer s1, sse2_byte_buffer s2 )
{
for ( int mask = 0; ; s1 += sizeof( __m128i ), s2 += sizeof(
__m128i ) )
{
__m128i m1 = *( __m128i* )( s1 );
__m128i m2 = *( __m128i* )( s2 );
__m128i r1 = not( _mm_cmpeq_epi8( m1, m2 ) );
__m128i zero = { 0 };
__m128i r2 = _mm_cmpeq_epi8( m1, zero );
__m128i r3 = _mm_cmpeq_epi8( m2, zero );
__m128i r = _mm_or_si128( r1, _mm_or_si128( r2, r3 ) );
mask = _mm_movemask_epi8( r );
if ( mask )
{
unsigned index = __builtin_ffs( mask ) - 1;
return ( s1[ index ] - s2[ index ] );
}
}
}
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