Re: Why is using single-precision slower than using double-precision

koppel@omega.ee.lsu.edu (David M. Koppelman)
Wed, 23 Nov 1994 22:03:45 GMT

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Related articles
Why is using single-precision slower than using double-precision zxu@monalisa.usc.edu (1994-11-23)
Re: Why is using single-precision slower than using double-precision weaver@weitek.COM (1994-11-23)
Re: Why is using single-precision slower than using double-precision meissner@osf.org (1994-11-23)
Re: Why is using single-precision slower than using double-precision scott@cs.arizona.edu (1994-11-23)
Re: Why is using single-precision slower than using double-precision joelw@convex.convex.com (1994-11-23)
Re: Why is using single-precision slower than using double-precision koppel@omega.ee.lsu.edu (1994-11-23)
Re: Why is using single-precision slower than using double-precision bevan@cs.man.ac.uk (1994-11-23)
Re: Why is using single-precision slower than using double-precision luigi@paris.CS.Berkeley.EDU (1994-11-23)
Re: Why is using single-precision slower than using double-precision davidm@Rational.COM (1994-11-23)
Re: Why is using single-precision slower than using double-precision dsmentek@hpfcla.fc.hp.com (1994-11-23)
Re: Why is using single-precision slower than using double-precision trobey@taos.arc.unm.edu (1994-11-23)
Re: Why is using single-precision slower than using double-precision kenneta@hubcap.clemson.edu (1994-11-23)
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Newsgroups: comp.parallel,comp.arch,comp.compilers
From: koppel@omega.ee.lsu.edu (David M. Koppelman)
In-Reply-To: zxu@monalisa.usc.edu's message of Wed, 23 Nov 1994 00:38:40 GMT
Status: R
Originator: rmuise@dragon.acadiau.ca
Organization: Louisiana State University ECE Dept.
References: <3aqv5k$e27@monalisa.usc.edu>
Date: Wed, 23 Nov 1994 22:03:45 GMT

In article <3aqv5k$e27@monalisa.usc.edu> zxu@monalisa.usc.edu (Zhiwei Xu) writes:


> Can any one explain why a C program using single precision (float) is slower
> that the same code using double precision (double)? Please try the following
> code for computing pi. I have tried it on IBM RS6000/250, IBM SP2, Sun4, and
> Sun SS20, and got the same strange timing.


In the RS/6000 all floating point is double precision. When you specify
single-precision operations the double precision result is rounded,
this takes more time. Also, C (at least some implementations) does
computation in double-precision by default.












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