在进行算术运算或尝试打印(调试)这么大的数字时,我会失去精度:1234567890.123456789
我认为我的问题在于 $d(算术结果)和 $e 的格式化打印。我怎样才能强制长双打?我的 Perl 版本(SUN 上的 5.8.4)说这是可能的。sprintf 有一个长双精度的大小选项(q 或 L 或 ll),但我还没有弄清楚如何使用它,也不知道它是否适用于 printf。
编辑:我添加了 BigFloat,它有效!但我仍然想强制长双打。
尝试添加 1234567890 + 0.123456789 并减去 1234567890 - 0.123456789。
use Config;
use Math::BigFloat;
$a = 1234567890;
$b = 123456789;
$c = $b/1e9; # 0.123456789
$d = $a + $c; # not enough precision (32-bit or double?)
$e = sprintf("%d.%.9d",$a,$b); # combine as strings
$f = 1234567890.123456789; # for reference (not enough precision)
# Use BigFloat to bypass lack of longdbl
$aBig = Math::BigFloat->new("$a");
$dSum = $aBig->fadd("$c"); # $dSum = $a + $c
$aBig = Math::BigFloat->new("$a"); # <-- Need a new one for every operation?
$dDif = $aBig->fsub(abs("$c")); # $dDif = $a - $c
print "a $a\n"; # 1234567890
print "c $c\n"; # 0.123456789
print "d=a+c $d\n"; # 1234567890.12346 <-- **Problem**
print "dSum=a+c $dSum\n"; # 1234567890.123456789 <-- Solution
print "dDif=a-c $dDif\n"; # 1234567890.876543211 <-- Solution
print "e $e\n"; # 1234567890.123456789
print "f $f\n"; # 1234567890.12346 <-- double, 52-bit, not longdbl?
printf ("printf e 20.9f %20.9f\n",$e); # 1234567890.123456717 <-- **Problem**
printf ("printf dSum 20.9f %20.9f\n",$dSum); # 1234567890.123456717 <-- **Problem**
printf ("printf dSum 20s %20s\n",$dSum); # 1234567890.123456789
printf ("printf dDif 20.9f %20.9f\n",$dDif); # 1234567890.876543283 <-- **Problem**
printf ("printf dDif 20s %20s\n",$dDif); # 1234567890.876543211
print "uselongdouble $Config{uselongdouble}\n"; # empty. No long doubles by default
print "d_longdbl $Config{d_longdbl}\n"; # "define". Supports long doubles
print "size double longdbl $Config{doublesize} $Config{longdblsize}\n"; # Ans 8 16
我还使用此代码来尝试理解类型,但没有太大帮助。有没有人用它来解释这样的问题?
use Devel::Peek 'Dump';
Dump ($dSum); # Wow, it's complicated
Dump ($f);