如何在不损失精度的情况下打印Perl bignum？

问题描述：

#!/usr/bin/perl
use strict;
use warnings;
my $s = "1234567890.123456789";
{   
    no bignum; printf "bignum==%s\n", bignum::in_effect() // 0;  
    my $x = $s; 
    printf "%29s\n", $x; 
    printf "%29.9f\n\n", $x; 
}   
{   
    use bignum; printf "bignum==%s\n", bignum::in_effect() // 0;
    my $x = $s; 
    printf "%29s\n", $x; 
    printf "%29.9f\n\n", $x; 
}

我的Perl的printf（为darwin-thread-multi- 2级），即使使用bignum，使用％f转换也无法兑现超过1e-6位的值：

My Perl's printf (ActiveState v5.10.1 built for darwin-thread-multi-2level) using the %f conversion doesn't honor my value past the 1e-6 digit, even when using bignum:

$ t.pl
bignum==0
         1234567890.123456789
         1234567890.123456717

bignum==1
         1234567890.123456789
         1234567890.123456717

如何打印我的输入而不会丢失精度？

How can I print my input without losing precision?

我的 real 问题是我将需要操纵这个数字（例如，$ x / 0.000_000_001，或更糟糕的是，$ x / 0.000_001_024，我不能用substr（）函数调用来伪造该数字）），但目前的减排措施使我感到困惑，甚至无法进入乐趣部分。

My real problem is that I'm going to need to manipulate this number (e.g., $x/0.000_000_001, or, worse, $x/0.000_001_024, which I can't fake with substr() function calls), but the current abatement has stumped me before I can even get to the "fun" part.

答

Perl的 printf 并没有真正实现bignums。使用 Math :: BigFloat 方法之一来获取字符串。因为这样做

Perl's printf doesn't really do bignums. Use one of the Math::BigFloat methods for getting a string. Since doing

my $x = $s;

只复制字符串，就必须做类似的事情

just copies the string, you'll have to do something like

my $x = 0+$s;

，因此 $ x 是一个数学运算：：BigFloat。然后类似

so that $x is a Math::BigFloat. Then something like

printf "%29s\n", $x->ffround(-9);

应该做你想做的事。

如何在不损失精度的情况下打印Perl bignum？

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