Re: Re: Re: Re: Re: infinite loop on while (@array)

But if I try the for example that demerphq quotes under Perl 5.5.3 (on FreeBSD), I get ...

for (;;) ne for (EXPR; EXPR; EXPR). The expressionless C-style for is special: it's an infinite loop. while (1) would be very inefficient, because it would have to check an expression on every iteration. Perl is smart, and knows what you're doing, and optimizes as follows:

2;0 juerd@ouranos:/root$ perl -MO=Deparse -e'while (1) { print }'
for (;;) {
    print $_;
}
-e syntax OK
[download]

You see? it's converted to for (;;) because it's more effecient. We can't benchmark the difference because of this optimization...

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Re: Re: Re: Re: Re: Re: infinite loop on while (@array) by demerphq (Chancellor) on Mar 27, 2002 at 15:40 UTC
You see? it's converted to for (;;) because it's more effecient. We can't benchmark the difference because of this optimization... Hmm, im sorry but this is inconclusive to me. The output of B::Deparse is not necessarily exactly what is happening under the hood (as I said to kanji above). Now you may be correct that perl optimizes for(;;) and while(1) into the same construct, but nothing ive seen posted here shows what that construct is. BTW a benchmark of while(1) versus for(;;) is as follows: `Benchmark: timing 1000000 iterations of for(;;), while(1)... for(;;): 71 wallclock secs (71.66 usr + 0.00 sys = 71.66 CPU) @ 13 +955.57/s (n=1000000) while(1): 71 wallclock secs (71.67 usr + 0.00 sys = 71.67 CPU) @ 13 +952.45/s (n=1000000) Rate while(1) for(;;) while(1) 13952/s -- -0% for(;;) 13956/s 0% --` [download] I agree this suggests they optimize down to the same thing.. :-) Yves / DeMerphq --- Writing a good benchmark isnt as easy as it might look.	[reply] [d/l]

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Re: Re: Re: Re: Re: Re: infinite loop on while (@array)
by demerphq (Chancellor) on Mar 27, 2002 at 15:40 UTC

You see? it's converted to for (;;) because it's more effecient. We can't benchmark the difference because of this optimization...

Hmm, im sorry but this is inconclusive to me. The output of B::Deparse is not necessarily exactly what is happening under the hood (as I said to kanji above). Now you may be correct that perl optimizes for(;;) and while(1) into the same construct, but nothing ive seen posted here shows what that construct is.

BTW a benchmark of while(1) versus for(;;) is as follows:

Benchmark: timing 1000000 iterations of for(;;), while(1)...
   for(;;): 71 wallclock secs (71.66 usr +  0.00 sys = 71.66 CPU) @ 13
+955.57/s (n=1000000)
  while(1): 71 wallclock secs (71.67 usr +  0.00 sys = 71.67 CPU) @ 13
+952.45/s (n=1000000)
            Rate while(1)  for(;;)
while(1) 13952/s       --      -0%
for(;;)  13956/s       0%       --
[download]

:-)

Yves / DeMerphq
---
Writing a good benchmark isnt as easy as it might look.

[reply]
[d/l]