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Re: What is acceptable for -ffast-math? (Was: associative law in combine)
- To: Theodore Papadopoulo <Theodore dot Papadopoulo at sophia dot inria dot fr>
- Subject: Re: What is acceptable for -ffast-math? (Was: associative law in combine)
- From: Gabriel Dos Reis <gdr at codesourcery dot com>
- Date: 01 Aug 2001 20:44:45 +0200
- Cc: Gabriel Dos Reis <gdr at codesourcery dot com>, dewar at gnat dot com, amylaar at redhat dot com, aoliva at redhat dot com, gcc at gcc dot gnu dot org, moshier at moshier dot ne dot mediaone dot net, torvalds at transmeta dot com, tprince at computer dot org
- Organization: CodeSourcery, LLC
- References: <200108011821.f71IL3d09937@mururoa.inria.fr>
Theodore Papadopoulo <Theodore.Papadopoulo@sophia.inria.fr> writes:
| [1 <text/plain; us-ascii (7bit)>]
| firstname.lastname@example.org said:
| > No, I do mean a transformation which does not dramatically transmute
| > the computations.
| That's not a definition.
Do you have one?
Changing 0.125 to 0.0 is a dramatic change.
| Dramatically, can mean very different things
| depending on the people and on the algorithms. That's basically the
| point that I'm trying to make. In many applications and algorithm
| the optimization a/b/c to a/(b*c) is meaningful and relevant.
In the case I showed, I was tring to compute a unit-length vector by
first scaling in order to avoid overflow (the /c part).
I'm not dismissing the fact that there are algorithms which would
benefit from optimizations. As I said earlier, I'm a fervent
proponent of optimizations. Not transformations which change the
computation in a very unexpected ways.