Re: while loop code generation

n8tm@aol.com (N8TM)
15 Dec 1997 21:56:25 -0500

          From comp.compilers
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From: n8tm@aol.com (N8TM)
Newsgroups: comp.compilers
Date: 15 Dec 1997 21:56:25 -0500
Organization: AOL http://www.aol.com
References: 97-12-112
Keywords: code, optimize

The conversion of while() to if()do...while() replace n unconditional
branches plus n conditional not taken and one conditional taken branch
with n+1 conditional branches, 2 of them not taken. This replacement
seems to be a de facto standard for C compilers, but not for FORTRAN
compilers unless they are based on a C compiler.


With some compilers, including g77, writing source code thus:


logical done
...
done = .false.
do while(.not. done)
....
done = ( .. )
if(done)exit
enddo


will avoid generation of code for testing at the top of the loop.


Tim
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