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Programming Perl

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The Standard Perl Library
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7.2.42 Math::BigFloat - Arbitrary-Length, Floating-Point Math Package

use Math::BigFloat;

$f = Math::BigFloat->new($string);

# NSTR is a number string; SCALE is an integer value.
# In all following cases $f remains unchanged.
# All methods except fcmp() return a number string.
$f->fadd(NSTR);          # return sum of NSTR and $f
$f->fsub(NSTR);          # return $f minus NSTR
$f->fmul(NSTR);          # return $f multiplied by NSTR
$f->fdiv(NSTR[,SCALE]);  # return $f divided by NSTR to SCALE places
$f->fneg();              # return negative of $f
$f->fabs();              # return absolute value of $f
$f->fcmp(NSTR);          # compare $f to NSTR; see below for return value
$f->fround(SCALE);       # return rounded value of $f to SCALE digits
$f->ffround(SCALE);      # return rounded value of $f at SCALEth place
$f->fnorm();             # return normalization of $f
$f->fsqrt([SCALE]);      # return sqrt of $f to SCALE places

This module allows you to use floating-point numbers of arbitrary length. For example:

$float = new Math::BigFloat "2.123123123123123123123123123123123";

Number strings (NSTRs) have the form, /[+-]\d*\.?\d*E[+-]\d+/. Embedded white space is ignored, so that the number strings used in the following two lines are identical:

$f = Math::BigFloat->new("-20.0    0732");
$g = $f->fmul("-20.00732");

The return value NaN indicates either that an input parameter was "Not a Number", or else that you tried to divide by zero or take the square root of a negative number. The fcmp() method returns -1, 0, or 1 depending on whether $f is less than, equal to, or greater than the number string given as an argument. If the number string is undefined or null, the undefined value is returned.

If SCALE is unspecified, division is computed to the number of digits given by:

max($div_scale, length(dividend)+length(divisor))

A similar default scale value is computed for square roots.

When you use this module, Perl's basic math operations are overloaded with routines from Math::BigFloat. Therefore, you don't have to employ the methods shown above to multiply, divide, and so on. You can rely instead on the usual operators. Given this code:

$f = Math::BigFloat->new("20.00732");
$g = Math::BigFloat->new("1.7");

the following six lines all yield the corresponding values for $h:

$h = 20.00732 * 1.7;    # 34.012444 (ordinary math--$h is not an object)
$h = $f * $g;           # "34.012444" ($h is now a BigFloat object)
$h = $f * 1.7;          # "34.012444" ($h is now a BigFloat object)
$h = 20.00732 * $g;     # "34.012444" ($h is now a BigFloat object)
$h = $f->fmul($g);      # "+34012444E-6" ($h is now a BigFloat object)
$h = $f->fmul(1.7);     # "+34012444E-6" ($h is now a BigFloat object)


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