Rob Herring robherring2@gmail.com writes:
On 12/17/2010 03:27 PM, Måns Rullgård wrote:
Rob Herringrobherring2@gmail.com writes:
From: Rob Herringrob.herring@calxeda.com
swab functions are heavily used by FDT code, so enable optimized assembly code for ARMv6 and later.
Signed-off-by: Rob Herringrob.herring@calxeda.com
arch/arm/include/asm/byteorder.h | 16 ++++++++++++++++ 1 files changed, 16 insertions(+), 0 deletions(-)
diff --git a/arch/arm/include/asm/byteorder.h b/arch/arm/include/asm/byteorder.h index c3489f1..9df5844 100644 --- a/arch/arm/include/asm/byteorder.h +++ b/arch/arm/include/asm/byteorder.h @@ -23,6 +23,22 @@ # define __SWAB_64_THRU_32__ #endif
+#if defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_6__) +static inline __u16 __attribute__((const)) ___arch_swab16(__u16 x) +{
- __asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
- return x;
+}
Pay close attention to what gcc does with this as it is prone to add unnecessary masking of the low halfword. If the callers are well-behaved (argument having top halfword clear), making the parameter and return types here plain unsigned (or u32) gives better code.
This straight from the Linux code and there are only a few users of swab16 (none in my build).
Look at the generated code if you don't believe me.