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* Add text and example regarding bindec() interpreting input as unsigned integers.

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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@278697 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Daniel Convissor 2009-04-14 14:53:47 +00:00
parent 61a41f2a4f
commit 40378a3f2b
1 changed files with 119 additions and 1 deletions
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120
reference/math/functions/bindec.xml
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@ -1,5 +1,5 @@
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.13 $ -->
<!-- $Revision: 1.14 $ -->
<refentry xml:id="function.bindec" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>bindec</refname>
@ -19,6 +19,13 @@
<function>bindec</function> converts a binary number to an
<type>integer</type> or, if needed for size reasons, <type>float</type>.
</para>
<para>
<function>bindec</function> interprets all
<parameter>binary_string</parameter> values as unsigned
integers. This is because <function>bindec</function> sees
the most significant bit as another order of magnitude
rather than as the sign bit.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
@ -87,6 +94,117 @@ echo bindec('111');
51
51
7
]]>
</screen>
</example>
</para>
<para>
<example>
<title><function>bindec</function> interprets input as unsigned integers</title>
<programlisting role="php">
<![CDATA[
<?php
/*
* The lesson from this example is in the output
* rather than the PHP code itself.
*/
$magnitude_lower = pow(2, (PHP_INT_SIZE * 8) - 2);
p($magnitude_lower - 1);
p($magnitude_lower, 'see the rollover?');
p(PHP_INT_MAX, 'PHP_INT_MAX');
p(~PHP_INT_MAX, 'interpreted to be one more than PHP_INT_MAX');
p(-1, 'interpreted to be the largest unsigned integer');
function p($input, $note = '') {
$format = '%0' . (PHP_INT_SIZE * 8) . 'b';
echo "input: $input\n";
$bin = sprintf($format, $input);
echo "binary: $bin\n";
$dec = bindec($bin);
echo 'bindec(): ' . $dec . "\n";
if (PHP_INT_SIZE == 8) {
echo 'dec as float: ' . sprintf('%f', $dec) . "\n";
echo "64 bit note: float lacks precision in this range\n";
}
if ($note) {
echo "NOTE: $note\n";
}
echo "\n";
}
?>
]]>
</programlisting>
&example.outputs.32bit;
<screen>
<![CDATA[
input: 1073741823
binary: 00111111111111111111111111111111
bindec(): 1073741823
input: 1073741824
binary: 01000000000000000000000000000000
bindec(): 1073741824
NOTE: see the rollover?
input: 2147483647
binary: 01111111111111111111111111111111
bindec(): 2147483647
NOTE: PHP_INT_MAX
input: -2147483648
binary: 10000000000000000000000000000000
bindec(): 2147483648
NOTE: interpreted to be one more than PHP_INT_MAX
input: -1
binary: 11111111111111111111111111111111
bindec(): 4294967295
NOTE: interpreted to be the largest unsigned integer
]]>
</screen>
&example.outputs.64bit;
<screen>
<![CDATA[
input: 4611686018427387903
binary: 0011111111111111111111111111111111111111111111111111111111111111
bindec(): 4611686018427387903
dec as float: 4611686018427387904.000000
64 bit note: float lacks precision in this range
input: 4611686018427387904
binary: 0100000000000000000000000000000000000000000000000000000000000000
bindec(): 4611686018427387904
dec as float: 4611686018427387904.000000
64 bit note: float lacks precision in this range
NOTE: see the rollover?
input: 9223372036854775807
binary: 0111111111111111111111111111111111111111111111111111111111111111
bindec(): 9223372036854775807
dec as float: 9223372036854775808.000000
64 bit note: float lacks precision in this range
NOTE: PHP_INT_MAX
input: -9223372036854775808
binary: 1000000000000000000000000000000000000000000000000000000000000000
bindec(): 9.2233720368548E+18
dec as float: 9223372036854775808.000000
64 bit note: float lacks precision in this range
NOTE: interpreted to be one more than PHP_INT_MAX
input: -1
binary: 1111111111111111111111111111111111111111111111111111111111111111
bindec(): 1.844674407371E+19
dec as float: 18446744073709551616.000000
64 bit note: float lacks precision in this range
NOTE: interpreted to be the largest unsigned integer
]]>
</screen>
</example>