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.
Also I've been told there were compilers that if using
for or while loops the generated code was
<initialize>
L1:
<evaluate condition>
je L2
<body>
jmp L1
L2:
Instead the do-while loop would have been
L1:
<body>
<evaluate condition>
jne L1
I.e. the code was better *for each iteration* (one conditional
jump instead of one conditional jump and one inconditional jump).
I think compiler got better since then, even if I don't think
they already so smart to be able to infer the "one interation
guaranteed" property to avoid the initial test that often.
Andrea
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