From: Laurent Desnogues <laurent.desnogues@gmail.com>
To: Bernd Schmidt <bernds@codesourcery.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: Add __builtin_clrsb, similar to clz/ctz
Date: Thu, 16 Jun 2011 13:56:00 -0000 [thread overview]
Message-ID: <BANLkTiksAbYnHPVU+-3n3VpiRB6ZzGe4ug@mail.gmail.com> (raw)
In-Reply-To: <4DF9FA9A.8040505@codesourcery.com>
On Thu, Jun 16, 2011 at 2:44 PM, Bernd Schmidt <bernds@codesourcery.com> wrote:
> Several processors have a "count redundant sign bits" instruction:
>
> * SIGNBITS on Blackfin
> * NORM on C6X
> * SBC, apparently, on picochip
picoChip defines __builtin_sbc. Wouldn't that make it redundant
with your __builtin_clrsb?
> and probably others. For example, for a value of 0 or -1, it returns 31,
> while e.g. an input 0xc0000000 produces 1.
FWIW, ARM AdvSIMD has vcls.
> Other compilers tend to define builtin functions called "norm" for this,
> and the operation is used in some DSP benchmarks. The patch below adds a
> __builtin_clrsb family of functions, similar to __builtin_clz. I'm open
> to suggestions about the name; I don't particularly like "norm" but
> maybe that's what users expect.
I'm not sure I like clrsb. The trailing 'b' looks superfluous if you
compare to clz. And clr looks too much like clear :-)
Laurent
next prev parent reply other threads:[~2011-06-16 13:10 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-16 13:06 Bernd Schmidt
2011-06-16 13:10 ` Georg-Johann Lay
2011-06-16 13:56 ` Laurent Desnogues [this message]
2011-06-16 13:59 ` Bernd Schmidt
2011-06-16 17:03 ` Richard Henderson
2011-06-20 20:32 ` Bernd Schmidt
2011-06-20 20:48 ` Richard Henderson
2011-06-21 16:39 ` [PATCH] Fix __bultin_clrsb* (PR middle-end/49489) Jakub Jelinek
2011-06-21 16:46 ` Bernd Schmidt
2011-06-23 6:23 ` Add __builtin_clrsb, similar to clz/ctz H.J. Lu
2011-07-12 3:50 ` Hans-Peter Nilsson
2011-08-23 10:07 ` Jakub Jelinek
2011-08-23 10:08 ` Bernd Schmidt
2011-08-23 10:19 ` Richard Guenther
2011-08-23 10:25 ` Jakub Jelinek
2011-08-23 10:34 ` Bernd Schmidt
2011-08-23 13:43 ` [PATCH] For FFS/CLZ/CTZ/CLRSB/POPCOUNT/PARITY/BSWAP require operand mode equal to operation mode (or VOIDmode) (PR middle-end/50161) Jakub Jelinek
2011-08-23 14:54 ` Georg-Johann Lay
2011-08-23 15:58 ` Jakub Jelinek
2011-08-23 16:16 ` Bernd Schmidt
2011-08-23 10:45 ` Add __builtin_clrsb, similar to clz/ctz Richard Sandiford
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