如何在 Perl 中创建或测试 NaN 或无穷大?

问题描述

如何在 Perl 中创建或测试 NaN 或无限值?

How do I create or test for NaN or infinite values in Perl?

推荐答案

这是一个相当可靠的方法:

Here's a fairly reliable way:

my $inf    = 9**9**9;
my $neginf = -9**9**9;
my $nan    = -sin(9**9**9);

sub isinf { $_[0]==9**9**9 || $_[0]==-9**9**9 }
sub isnan { ! defined( $_[0] <=> 9**9**9 ) }
# useful for detecting negative zero
sub signbit { substr( sprintf( '%g', $_[0] ), 0, 1 ) eq '-' }

for my $num ( $inf, $neginf, $nan ) {
   printf("%s:	isinf: %d,	isnan: %d,	signbit: %d
", $num, isinf($num), isnan($num), signbit($num));
}

输出为:

inf:    isinf: 1,   isnan: 0,   signbit: 0
-inf:   isinf: 1,   isnan: 0,   signbit: 1
nan:    isinf: 0,   isnan: 1,   signbit: 0

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