Re: Re: Testing a number for oddness

On constants, the AND may be getting optimized away, and in checking I find that it is...

# perl -MO=Deparse,-p -we "print 15 & 1"
print(1);
-e syntax OK
# perl -MO=Deparse,-p -we "print 16 & 1"
print(0);
-e syntax OK
[download]

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Comment on Re: Re: Testing a number for oddness Download Code

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Re: Re: Re: Testing a number for oddness by chipmunk (Parson) on Jan 23, 2001 at 09:40 UTC
It turns out that almost all operators in Perl get optimized away in this manner. 'Constant folding', as it's called, is a very common optimization. `% perl -MO=Deparse print 15 + 1, 15 - 1, 15 * 1, 15 % 1, 15 & 1, 15 ^ 1, 15 << 1, !15, 15 \|\| $x, 15 . 1, 15 < 1, 15 <=> 1, 15 ? $x : $y; __END__ print 16, 14, 15, 0, 1, 14, 30, 0, 15, '151', 0, 1, $x;` [download] In fact, the only operator I've found that could have this optimization but doesn't is x.	[reply] [d/l]
Re: Re: Re: Testing a number for oddness by runrig (Abbot) on Jan 23, 2001 at 08:35 UTC
That's why I set '$i' to a constant (my $i=15), then AND'ed it. I checked, and THAT won't get optimized away.	[reply]