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Re: PATH Optimized with SSE2 sinf and cof for x86_32

From: Rich Felker <dalias at aerifal dot cx>
To: Dmitrieva Liubov <liubov dot dmitrieva at gmail dot com>
Cc: libc-alpha at sourceware dot org
Date: Wed, 15 Aug 2012 12:27:03 -0400
Subject: Re: PATH Optimized with SSE2 sinf and cof for x86_32
References: <CAHjhQ91o6CU8CjWr1ut-H=78nFzyoMqG1RAGMJQcmhGx7_CBdg@mail.gmail.com>

On Wed, Aug 15, 2012 at 01:44:54PM +0400, Dmitrieva Liubov wrote:
> >> Please remove the Contributed line, we're not adding this anymore.
> 
> Done and reattached. Please review, I'm going to submit SSE sincos for
> x86_64 after this patch merge.

This code is wrong. You cannot perform argument reduction for large
arguments by using a single, double, or even extended-precision
approximation for pi. This bug (16 million ulps of error in sinf/cosf)
keeps getting reintroduced by well-meaning people who don't understand
the issue. Please test cosf(0x1p120) and sinf(0x1p120) before
proceeding with this. Their values should be:

cosf(0x1p+120) = -0.925879002
sinf(0x1p+120) = 0.377820104

Rich

Follow-Ups:
- Re: PATH Optimized with SSE2 sinf and cof for x86_32
  - From: Dmitrieva Liubov

References:
- Re: PATH Optimized with SSE2 sinf and cof for x86_32
  - From: Dmitrieva Liubov

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