a3e4943686
Patch from Nicolas Pitre Depending on your gcc version, the current C-only implementation would produce suboptimal code, ranging from a bad register selection forcing an additional mov instruction to a failure to merge the eor and the ror in a single instruction. With a little help gcc always produces the best code. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
57 lines
1.4 KiB
C
57 lines
1.4 KiB
C
/*
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* linux/include/asm-arm/byteorder.h
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*
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* ARM Endian-ness. In little endian mode, the data bus is connected such
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* that byte accesses appear as:
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* 0 = d0...d7, 1 = d8...d15, 2 = d16...d23, 3 = d24...d31
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* and word accesses (data or instruction) appear as:
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* d0...d31
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*
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* When in big endian mode, byte accesses appear as:
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* 0 = d24...d31, 1 = d16...d23, 2 = d8...d15, 3 = d0...d7
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* and word accesses (data or instruction) appear as:
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* d0...d31
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*/
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#ifndef __ASM_ARM_BYTEORDER_H
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#define __ASM_ARM_BYTEORDER_H
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#include <linux/compiler.h>
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#include <asm/types.h>
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static inline __attribute_const__ __u32 ___arch__swab32(__u32 x)
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{
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__u32 t;
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if (__builtin_constant_p(x)) {
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t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
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} else {
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/*
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* The compiler needs a bit of a hint here to always do the
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* right thing and not screw it up to different degrees
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* depending on the gcc version.
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*/
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asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
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}
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x = (x << 24) | (x >> 8); /* mov r0,r0,ror #8 */
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t &= ~0x00FF0000; /* bic r1,r1,#0x00FF0000 */
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x ^= (t >> 8); /* eor r0,r0,r1,lsr #8 */
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return x;
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}
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#define __arch__swab32(x) ___arch__swab32(x)
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#if !defined(__STRICT_ANSI__) || defined(__KERNEL__)
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# define __BYTEORDER_HAS_U64__
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# define __SWAB_64_THRU_32__
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#endif
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#ifdef __ARMEB__
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#include <linux/byteorder/big_endian.h>
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#else
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#include <linux/byteorder/little_endian.h>
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#endif
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#endif
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