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ARM: 7173/1: Add optimised swahb32() byteswap helper for v6 and above
ARMv6 and later processors have the REV16 instruction, which swaps the bytes within each halfword of a register value. This is already used to implement swab16(), but since the native operation performaed by REV16 is actually swahb32(), this patch renames the existing swab16() helper accordingly and defines __arch_swab16() in terms of it. This allows calls to both swab16() and swahb32() to be optimised. The compiler's generated code might improve someday, but as of 4.5.2 the code generated for pure C implementing these 16-bit bytesswaps remains pessimal. swahb32() is useful for converting 32-bit Thumb instructions between integer and memory representation on BE8 platforms (among other uses). Signed-off-by: Dave Martin <dave.martin@linaro.org> Reviewed-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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@ -24,12 +24,13 @@
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#if defined(__KERNEL__) && __LINUX_ARM_ARCH__ >= 6
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static inline __attribute_const__ __u16 __arch_swab16(__u16 x)
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static inline __attribute_const__ __u32 __arch_swahb32(__u32 x)
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{
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__asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
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return x;
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}
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#define __arch_swab16 __arch_swab16
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#define __arch_swahb32 __arch_swahb32
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#define __arch_swab16(x) ((__u16)__arch_swahb32(x))
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static inline __attribute_const__ __u32 __arch_swab32(__u32 x)
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{
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