/usr/share/perl5/JE/Object/Number/maxvalue.pl is in libje-perl 0.056-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 | # This is basically Data::Float 0.009 with everything stripped out that is
# not needed.
# From Data::Float 0.009:
# Copyright (C) 2006, 2007, 2008 Andrew Main (Zefram) <zefram fysh.org>
use warnings;
use strict;
package JE::Object::Number::_maxvalue;
use Carp 'croak';
#
# mult_pow2() multiplies a specified value by a specified power of two.
# This is done using repeated multiplication, and can cope with cases
# where the power of two cannot be directly represented as a floating
# point value. (E.g., 0x1.b2p-900 can be multiplied by 2^1500 to get
# to 0x1.b2p+600; the input and output values can be represented in
# IEEE double, but 2^1500 cannot.) Overflow and underflow can occur.
#
# @powtwo is an array such that powtwo[i] = 2^2^i. Its elements are
# used in the repeated multiplication in mult_pow2. Similarly,
# @powhalf is such that powhalf[i] = 2^-2^i. Reading the exponent
# in binary indicates which elements of @powtwo/@powhalf to multiply
# by, except that it may indicate elements that don't exist, either
# because they're not representable or because the arrays haven't
# been filled yet. mult_pow2() will use the last element of the array
# repeatedly in this case. Thus array elements after the first are
# only an optimisation, and do not change behaviour.
#
my @powtwo = (2.0);
my @powhalf = (0.5);
sub mult_pow2($$) {
my($value, $exp) = @_;
return $_[0] if $value == 0.0;
my $powa = \@powtwo;
if($exp < 0) {
$powa = \@powhalf;
$exp = -$exp;
}
for(my $i = 0; $i != $#$powa && $exp != 0; $i++) {
$value *= $powa->[$i] if $exp & 1;
$exp >>= 1;
}
$value *= $powa->[-1] while $exp--;
return $value;
}
#
# Range of finite exponent values.
#
my $min_finite_exp;
my $max_finite_exp;
my $max_finite_pow2;
my $min_finite;
my @directions = (
{
expsign => -1,
powa => \@powhalf,
xexp => \$min_finite_exp,
xpower => \$min_finite,
},
{
expsign => +1,
powa => \@powtwo,
xexp => \$max_finite_exp,
xpower => \$max_finite_pow2,
},
);
while(!$directions[0]->{done} || !$directions[1]->{done}) {
foreach my $direction (@directions) {
next if $direction->{done};
my $lastpow = $direction->{powa}->[-1];
my $nextpow = $lastpow * $lastpow;
unless(mult_pow2($nextpow, -$direction->{expsign} *
(1 << (@{$direction->{powa}} - 1)))
== $lastpow) {
$direction->{done} = 1;
next;
}
push @{$direction->{powa}}, $nextpow;
}
}
foreach my $direction (@directions) {
my $expsign = $direction->{expsign};
my $xexp = 1 << (@{$direction->{powa}} - 1);
my $extremum = $direction->{powa}->[-1];
for(my $addexp = $xexp; $addexp >>= 1; ) {
my $nx = mult_pow2($extremum, $expsign*$addexp);
if(mult_pow2($nx, -$expsign*$addexp) == $extremum) {
$xexp += $addexp;
$extremum = $nx;
}
}
${$direction->{xexp}} = $expsign * $xexp;
${$direction->{xpower}} = $extremum;
}
#
# pow2() generates a power of two from scratch. It complains if given
# an exponent that would make an unrepresentable value.
#
sub pow2($) {
my($exp) = @_;
croak "exponent $exp out of range [$min_finite_exp, $max_finite_exp]"
unless $exp >= $min_finite_exp && $exp <= $max_finite_exp;
return mult_pow2(1.0, $exp);
}
#
# Significand size.
#
my($significand_bits, $significand_step);
{
my $i;
for($i = 1; ; $i++) {
my $tryeps = $powhalf[$i];
last unless (1.0 + $tryeps) - 1.0 == $tryeps;
}
$i--;
$significand_bits = 1 << $i;
$significand_step = $powhalf[$i];
while($i--) {
my $tryeps = $significand_step * $powhalf[$i];
if((1.0 + $tryeps) - 1.0 == $tryeps) {
$significand_bits += 1 << $i;
$significand_step = $tryeps;
}
}
}
my $max_finite = $max_finite_pow2 -
pow2($max_finite_exp - $significand_bits - 1);
$max_finite += $max_finite;
$JE::Object::Number::max_finite = $max_finite;
$JE::Object::Number::min_finite = $min_finite;
package main; # Is it safe to delete a package from inside it?
require Symbol;
Symbol::delete_package('JE::Object::Number::_maxvalue');
|