In article <[EMAIL PROTECTED]>,
Andrea Griffini <[EMAIL PROTECTED]> wrote:
> On Sat, 18 Jun 2005 13:35:16 -0000, Grant Edwards <[EMAIL PROTECTED]>
> wrote:
>
> >AFAICT, the main use for do/while in C is when you want to
> >define a block of code with local variables as a macro:
>
> When my job was squeezing most out of the CPU (videogame
> industry) I remember that the asm code generated by
>
> while (sz-- > 0)
> {
> /* do some stuff */
> }
>
> was indeed worse than
>
> do
> {
> /* do some stuff */
> } while (--sz);
>
> because of the initial "empty-loop" test (conditional jumps
> were bad, and forward conditional jumps were worse).
> So where at least one iteration was guaranteed the do-while
> loop was a better choice.
Hmm. I don't know what compiler you were using, but in my experience
it's fairly typical to compile while(<test> ...) { <body> ... } as
j test
body: <body>
...
test: <test>
...
je body ;; or whatever your condition is
To turn this into a do { <body> ... } while(<test> ...), you need only
remove the initial "j test" instruction. Even if forward conditional
jumps are bad for your particular architecture, this method avoids the
problem neatly.
Personally, I'd be pretty suspicious of the quality of a compiler that
produced radically different code for these two constructs without some
damned good reason.
-M
--
Michael J. Fromberger | Lecturer, Dept. of Computer Science
http://www.dartmouth.edu/~sting/ | Dartmouth College, Hanover, NH, USA
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