Michael Brown
af96c4151c
Use the "bswap" instruction to shrink the size of byte-swapping code,
and provide the in-place variants __bswap_{16,32,64}s.
"bswap" is available only on 486 and later processors. (We already
assume the presence of "cpuid" and "rdtsc", which are available only
on Pentium and later processors.)
Signed-off-by: Michael Brown <mcb30@ipxe.org>
68 lines
1.6 KiB
C
68 lines
1.6 KiB
C
#ifndef _BITS_BYTESWAP_H
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#define _BITS_BYTESWAP_H
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/** @file
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*
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* Byte-order swapping functions
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*
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*/
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#include <stdint.h>
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FILE_LICENCE ( GPL2_OR_LATER );
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static inline __attribute__ (( always_inline, const )) uint16_t
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__bswap_variable_16 ( uint16_t x ) {
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__asm__ ( "xchgb %b0,%h0" : "=q" ( x ) : "0" ( x ) );
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return x;
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}
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static inline __attribute__ (( always_inline )) void
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__bswap_16s ( uint16_t *x ) {
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__asm__ ( "rorw $8, %0" : "=g" ( *x ) : "0" ( *x ) );
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}
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static inline __attribute__ (( always_inline, const )) uint32_t
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__bswap_variable_32 ( uint32_t x ) {
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__asm__ ( "bswapl %0" : "=r" ( x ) : "0" ( x ) );
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return x;
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}
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static inline __attribute__ (( always_inline )) void
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__bswap_32s ( uint32_t *x ) {
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__asm__ ( "bswapl %0" : "=r" ( *x ) : "0" ( *x ) );
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}
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static inline __attribute__ (( always_inline, const )) uint64_t
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__bswap_variable_64 ( uint64_t x ) {
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uint32_t in_high = ( x >> 32 );
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uint32_t in_low = ( x & 0xffffffffUL );
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uint32_t out_high;
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uint32_t out_low;
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__asm__ ( "bswapl %0\n\t"
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"bswapl %1\n\t"
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"xchgl %0,%1\n\t"
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: "=r" ( out_high ), "=r" ( out_low )
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: "0" ( in_high ), "1" ( in_low ) );
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return ( ( ( ( uint64_t ) out_high ) << 32 ) |
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( ( uint64_t ) out_low ) );
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}
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static inline __attribute__ (( always_inline )) void
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__bswap_64s ( uint64_t *x ) {
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uint32_t __attribute__ (( may_alias )) *dwords = ( ( void * ) x );
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uint32_t discard;
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__asm__ ( "movl %0,%2\n\t"
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"bswapl %2\n\t"
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"xchgl %2,%1\n\t"
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"bswapl %2\n\t"
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"movl %2,%0\n\t"
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: "=g" ( dwords[0] ), "=g" ( dwords[1] ), "=r" ( discard )
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: "0" ( dwords[0] ), "1" ( dwords[1] ) );
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}
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#endif /* _BITS_BYTESWAP_H */
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