[PATCH v5 1/3] lib: add bitrev8x4()

Joshua Clayton
2016-12-07T21:19:23Z

Add a function to reverse bytes within a 32 bit word.
This function is more efficient than using the 8 bit version when
iterating over an array

Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
---
arch/arm/include/asm/bitrev.h | 6 ++++++
include/linux/bitrev.h | 26 ++++++++++++++++++++++++++
2 files changed, 32 insertions(+)

diff --git a/arch/arm/include/asm/bitrev.h b/arch/arm/include/asm/bitrev.h
index ec291c3..9482f78 100644
--- a/arch/arm/include/asm/bitrev.h
+++ b/arch/arm/include/asm/bitrev.h
@@ -17,4 +17,10 @@ static __always_inline __attribute_const__ u8 __arch_bitrev8(u8 x)
return __arch_bitrev32((u32)x) >> 24;
}

+static __always_inline __attribute_const__ u32 __arch_bitrev8x4(u32 x)
+{
+ __asm__ ("rbit %0, %1; rev %0, %0" : "=r" (x) : "r" (x));
+ return x;
+}
+
#endif
diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
index fb790b8..b1cfa1a 100644
--- a/include/linux/bitrev.h
+++ b/include/linux/bitrev.h
@@ -9,6 +9,7 @@
#define __bitrev32 __arch_bitrev32
#define __bitrev16 __arch_bitrev16
#define __bitrev8 __arch_bitrev8
+#define __bitrev8x4 __arch_bitrev8x4

#else
extern u8 const byte_rev_table[256];
@@ -27,6 +28,14 @@ static inline u32 __bitrev32(u32 x)
return (__bitrev16(x & 0xffff) << 16) | __bitrev16(x >> 16);
}

+static inline u32 __bitrev8x4(u32 x)
+{
+ return(__bitrev8(x & 0xff) |
+ (__bitrev8((x >> 8) & 0xff) << 8) |
+ (__bitrev8((x >> 16) & 0xff) << 16) |
+ (__bitrev8((x >> 24) & 0xff) << 24));
+}
+
#endif /* CONFIG_HAVE_ARCH_BITREVERSE */

#define __constant_bitrev32(x) \
@@ -50,6 +59,15 @@ static inline u32 __bitrev32(u32 x)
__x; \
})

+#define __constant_bitrev8x4(x) \
+({ \
+ u32 __x = x; \
+ __x = ((__x & (u32)0xF0F0F0F0UL) >> 4) | ((__x & (u32)0x0F0F0F0FUL) << 4); \
+ __x = ((__x & (u32)0xCCCCCCCCUL) >> 2) | ((__x & (u32)0x33333333UL) << 2); \
+ __x = ((__x & (u32)0xAAAAAAAAUL) >> 1) | ((__x & (u32)0x55555555UL) << 1); \
+ __x; \
+})
+
#define __constant_bitrev8(x) \
({ \
u8 __x = x; \
@@ -75,6 +93,14 @@ static inline u32 __bitrev32(u32 x)
__bitrev16(__x); \
})

+#define bitrev8x4(x) \
+({ \
+ u32 __x = x; \
+ __builtin_constant_p(__x) ? \
+ __constant_bitrev8x4(__x) : \
+ __bitrev8x4(__x); \
+})
+
#define bitrev8(x) \
({ \
u8 __x = x; \
--
2.9.3