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[i386] Optimise byte-swapping functions and provide __bswap_{16,32,64}s() 

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>
This commit is contained in:
Michael Brown 2012-03-04 15:06:45 +00:00
parent 4a32308b40
commit af96c4151c
1 changed files with 56 additions and 32 deletions
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88
src/arch/i386/include/bits/byteswap.h
View File

@ -1,43 +1,67 @@
#ifndef ETHERBOOT_BITS_BYTESWAP_H
#define ETHERBOOT_BITS_BYTESWAP_H
#ifndef _BITS_BYTESWAP_H
#define _BITS_BYTESWAP_H
/** @file
*
* Byte-order swapping functions
*
*/
#include <stdint.h>
FILE_LICENCE ( GPL2_OR_LATER );
static inline __attribute__ ((always_inline, const)) uint16_t
__bswap_variable_16(uint16_t x)
{
__asm__("xchgb %b0,%h0\n\t"
: "=q" (x)
: "0" (x));
static inline __attribute__ (( always_inline, const )) uint16_t
__bswap_variable_16 ( uint16_t x ) {
__asm__ ( "xchgb %b0,%h0" : "=q" ( x ) : "0" ( x ) );
return x;
}
static inline __attribute__ ((always_inline, const)) uint32_t
__bswap_variable_32(uint32_t x)
{
__asm__("xchgb %b0,%h0\n\t"
"rorl $16,%0\n\t"
"xchgb %b0,%h0"
: "=q" (x)
: "0" (x));
static inline __attribute__ (( always_inline )) void
__bswap_16s ( uint16_t *x ) {
__asm__ ( "rorw $8, %0" : "=g" ( *x ) : "0" ( *x ) );
}
static inline __attribute__ (( always_inline, const )) uint32_t
__bswap_variable_32 ( uint32_t x ) {
__asm__ ( "bswapl %0" : "=r" ( x ) : "0" ( x ) );
return x;
}
static inline __attribute__ ((always_inline, const)) uint64_t
__bswap_variable_64(uint64_t x)
{
union {
uint64_t qword;
uint32_t dword[2];
} u;
u.qword = x;
u.dword[0] = __bswap_variable_32(u.dword[0]);
u.dword[1] = __bswap_variable_32(u.dword[1]);
__asm__("xchgl %0,%1"
: "=r" ( u.dword[0] ), "=r" ( u.dword[1] )
: "0" ( u.dword[0] ), "1" ( u.dword[1] ) );
return u.qword;
static inline __attribute__ (( always_inline )) void
__bswap_32s ( uint32_t *x ) {
__asm__ ( "bswapl %0" : "=r" ( *x ) : "0" ( *x ) );
}
#endif /* ETHERBOOT_BITS_BYTESWAP_H */
static inline __attribute__ (( always_inline, const )) uint64_t
__bswap_variable_64 ( uint64_t x ) {
uint32_t in_high = ( x >> 32 );
uint32_t in_low = ( x & 0xffffffffUL );
uint32_t out_high;
uint32_t out_low;
__asm__ ( "bswapl %0\n\t"
"bswapl %1\n\t"
"xchgl %0,%1\n\t"
: "=r" ( out_high ), "=r" ( out_low )
: "0" ( in_high ), "1" ( in_low ) );
return ( ( ( ( uint64_t ) out_high ) << 32 ) |
( ( uint64_t ) out_low ) );
}
static inline __attribute__ (( always_inline )) void
__bswap_64s ( uint64_t *x ) {
uint32_t __attribute__ (( may_alias )) *dwords = ( ( void * ) x );
uint32_t discard;
__asm__ ( "movl %0,%2\n\t"
"bswapl %2\n\t"
"xchgl %2,%1\n\t"
"bswapl %2\n\t"
"movl %2,%0\n\t"
: "=g" ( dwords[0] ), "=g" ( dwords[1] ), "=r" ( discard )
: "0" ( dwords[0] ), "1" ( dwords[1] ) );
}
#endif /* _BITS_BYTESWAP_H */