Re: [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions

["H. Peter Anvin" <hpa@xxxxxxxxx>]

On 01/19/2015 02:04 AM, Peter Zijlstra wrote:
> On Mon, Jan 19, 2015 at 07:54:22AM +1200, Linus Torvalds wrote:
>> Why?
>>
>> The 8- and 16- bit versions are the same as the 32-bit one. This seems
>> pointless. If you want something where the sign is in bit 3, they all
>> return the same value, just the return type differs, but that's really a
>> *caller* thing, no?
> 
> Even for the 8bit ones? Since we have the *H and *L register we have
> more 8 bit regs than we have 16/32 bit regs and it might just be worth
> it.

Fewer, actually.  gcc doesn't really use the H registers much, and
instead considers 8-bit values to occupy the whole register, but that
means only four are available in 32-bit mode.

	-hpa

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