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Date: Mon, 16 Mar 1998 00:39:18 +0000
Cc: beastium <beastium-list AT Desk DOT nl>
From: Paul Shirley <Paul AT chocolat DOT foobar DOT co DOT uk>
Subject: Re: paranoia & extra precision [was -fno-float-store in pgcc]
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In message <19980312074656 DOT 14562 AT cerebro DOT laendle>, Marc Lehmann
<pcg AT goof DOT com> writes
>This is why the loop stops at y = 5*10^-17. This is compliant to the ieee
>rule that intermediate values have to be at the same precision as the
>result.
>
>Now, when optimizing, gcc tries to keep values in the floating point
>registers. But other than, say, the m68k fpu, the x86 fpu has no notion of
>different data types, all fpu registers have the same type, long double (80
>bits extended format). 80 bits extended format => 64 bits mantissa => ~19
>digits precision.

This puzzles me, in the past I have had to force various C compilers to
keep intermediates on the fpu stack (by defining them as long doubles),
even when optimising. Is a C compiler really allowed to make this change
without explicit permission? (ie not just a general -On flag)

-- 
Paul Shirley