Re: [eigen] SSE square root |

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] SSE square root*From*: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>*Date*: Fri, 27 Mar 2009 11:28:15 +0100*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=XNT1VGornaeLJWmBgavyER05Ezq8xsp+sqQLwKD+2bg=; b=nAy4PlZdaTtATucmqGBIFlQyxj0waSfhqjoAnGXln0iJRGhvaIntkEC6WE42ywFWw8 jm5lS9uZj0z9Ohfjf5vO524r+C/MbGXU62Xo8Jj3FecsdJUvBeja98iYH+lXe8A7hG4Q I1zHnrbFmpljQtQUDG+AOINzmowpn5L4EaNOQ=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=FGq5FMjemKA9el6Kyn7DYK8IczK8OVgbjZn9l/NoZg8tTvU4XiPAUGqBs79hhUMHqQ pJSXtez3ZqvFTgj6XQC2X0TRc9NyYuI04l4g012/nwjjw7GPWfrbZc61jqYAMyT7nzyo p6iJOBDjh30cJKo5vYr339/9ODY7vJNmJcb0I=

On Fri, Mar 27, 2009 at 8:32 AM, Rohit Garg <rpg.314@xxxxxxxxx> wrote: > This file has my sse float implementation for square root. The SSE > square root instruction has only 12 bits of precision so extra where did you find sqrtss or sqrtps has only 12 bits of precision ? this is right for the reciprocal functions (rcpps and rsqrtps) but I thought sqrtps was ieee754 compliant. For instance I found that in the glibc: float __ieee754_sqrtf (float x) { float res; asm ("sqrtss %0, %1" : "=x" (res) : "x" (x)); return res; } anyway, sqrtps is very slow and I'm sure there exist a faster alternative. Perhaps a rsqrtps followed by a div and Newton Raphson iterations.. > iterations of Newton Raphson may be neccessary. How many of the are > neccessary, I don't know. the max error I was getting was O(1e-8) in > [0,1]. The cephes implementation has square root only for limited > range. They do some other hacks to take care of range. I'll look into > implementing those later. For now, this should be an acceptable for > the fast implementations of square root atleast. > Regards, > > -- > Rohit Garg > > http://rpg-314.blogspot.com/ > > Senior Undergraduate > Department of Physics > Indian Institute of Technology > Bombay >

**Follow-Ups**:**Re: [eigen] SSE square root***From:*Gael Guennebaud

**Re: [eigen] SSE square root***From:*Rohit Garg

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