Re: Problems with Hardware, Languages, and Compilers

smryan@mail.com (!@?*$%) writes:


> > Factorizing x/y as x*(1/y) is not generally done inside compilers,
> > because compiler people are generally given a quotient hardware
> > operation, rather than an inverse operation. The software that cares
>
> Nope. It is generally not done because customers scream bloody murder
> if the last few bits are different, which can easily happen with this
> transformation.
>
> Personal experience.


However, it can (and is) be done when 1/y is exactly representable. For
example, consider:


double foo(double a){ return a/4; }


The current development version of the GNU C powerpc compiler generates:


.section ".rodata"
.align 3
.LC0:
.double 0d2.50000000000000000000e-1
.section ".text"
.align 2
.globl foo
.type foo,@function
foo:
addis 9,0,.LC0@ha
addi 9,9,.LC0@l
lfd 0,0(9)
fmul 1,1,0
blr


--
Michael Meissner, Cygnus Solutions (East Coast)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA
meissner@cygnus.com, 617-354-5416 (office), 617-354-7161 (fax)


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