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Re: [PATCH][BZ #14412] Define __sincos_finite as a fast version of sincos
- From: Andrew Haley <aph at redhat dot com>
- To: OndÅej BÃlka <neleai at seznam dot cz>
- Cc: "Joseph S. Myers" <joseph at codesourcery dot com>, Siddhesh Poyarekar <siddhesh at redhat dot com>, libc-alpha at sourceware dot org, libc-ports at sourceware dot org
- Date: Mon, 29 Apr 2013 15:53:00 +0100
- Subject: Re: [PATCH][BZ #14412] Define __sincos_finite as a fast version of sincos
- References: <20130429102739 dot GE1330 at spoyarek dot pnq dot redhat dot com> <Pine dot LNX dot 4 dot 64 dot 1304291332320 dot 10827 at digraph dot polyomino dot org dot uk> <20130429141553 dot GC24033 at domone dot kolej dot mff dot cuni dot cz>
On 04/29/2013 03:15 PM, OndÅej BÃlka wrote:
> On Mon, Apr 29, 2013 at 01:34:42PM +0000, Joseph S. Myers wrote:
>> On Mon, 29 Apr 2013, Siddhesh Poyarekar wrote:
>>
>>> This patch brings back the assembly implementation of sincos (with
>>> some changes) to give a fast alternative to the default sincos
>>> implementation. This is defined as __sincos_finite and is used if the
>>> implementing program is compiled with the -ffinite-math-only gcc flag.
>>
>> The changes don't seem to include accurate range reduction. Without that,
>> I think this is inappropriate, as it will result in wildly inaccurate
>> results for large but finite inputs.
>>
> These inputs contain zero significant digits. You cannot expect any
> accuracty from them.
You can't possibly know that. If the caller asks for sin(2^80) you should
return a close approximation to sin(2^80), not garbage.
Andrew.