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Re: [ft-devel] assembler or builtin?
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From: |
Alexei Podtelezhnikov |
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Subject: |
Re: [ft-devel] assembler or builtin? |
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Date: |
Thu, 10 Jul 2014 22:43:39 -0400 |
On Mon, Jul 7, 2014 at 4:24 PM, Behdad Esfahbod <address@hidden> wrote:
> On 14-07-07 03:01 PM, Alexei Podtelezhnikov wrote:
>> Many architectures have special instructions for the most significant
>> bit: BSR on x86, CLZ on ARM. Some compilers have builtin functions for
>> that too: __builtin_clz in gcc, _BitScanReverse in VC2005 and up. What
>> would be a preferred way of using this functionality in freetype
>> for FT_MSB?
>
> I suggest using the builtins and letting the compiler designers write the
> assembler.
The proposed patch is attached. It utilizes gcc builtins to optimize
FT_MSB. FT_CONFIG_OPTION_NO_ASSEMBLER will disable it if necessary.
Please comment.
msb.patch
Description: Text Data