[U-Boot] [PATCH] arm: Add armv6 and armv7 optimized swab functions

[Måns Rullgård]

Rob Herring <robherring2 at gmail.com> writes:

> On 12/17/2010 03:27 PM, Måns Rullgård wrote:
>> Rob Herring<robherring2 at gmail.com>  writes:
>>
>>> From: Rob Herring<rob.herring at calxeda.com>
>>>
>>> swab functions are heavily used by FDT code, so enable
>>> optimized assembly code for ARMv6 and later.
>>>
>>> Signed-off-by: Rob Herring<rob.herring at 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.

-- 
Måns Rullgård
mans at mansr.com