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Implement without-bcmath compatible UnitConverter. We might want to factor our floating point fudges. These calculations are only accurate for small precisions, and are architecture-dependent. (Unit tests seem to work on 32bit, though).

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git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1752 48356398-32a2-884e-a903-53898d9a118a
This commit is contained in:
Edward Z. Yang
2008-05-21 00:29:31 +00:00
parent 64b5581bf2
commit 6d7a17e9b6
3 changed files with 81 additions and 25 deletions
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86
library/HTMLPurifier/UnitConverter.php
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@@ -43,9 +43,15 @@ class HTMLPurifier_UnitConverter
*/
protected $internalPrecision;
public function __construct($output_precision = 4, $internal_precision = 10) {
/**
* Whether or not BCMath is available
*/
private $bcmath;
public function __construct($output_precision = 4, $internal_precision = 10, $force_no_bcmath = false) {
$this->outputPrecision = $output_precision;
$this->internalPrecision = $internal_precision;
$this->bcmath = !$force_no_bcmath && function_exists('bcmul');
}
/**
@@ -109,8 +115,8 @@ class HTMLPurifier_UnitConverter
// Do the conversion if necessary
if ($dest_unit !== $unit) {
$factor = bcdiv(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
$n = bcmul($n, $factor, $cp);
$factor = $this->div(self::$units[$state][$unit], self::$units[$state][$dest_unit], $cp);
$n = $this->mul($n, $factor, $cp);
$unit = $dest_unit;
}
@@ -135,7 +141,7 @@ class HTMLPurifier_UnitConverter
// Pre-condition: $i == 0
// Perform conversion to next system of units
$n = bcmul($n, self::$units[$state][$dest_state][1], $cp);
$n = $this->mul($n, self::$units[$state][$dest_state][1], $cp);
$unit = self::$units[$state][$dest_state][2];
$state = $dest_state;
@@ -146,26 +152,11 @@ class HTMLPurifier_UnitConverter
// Post-condition: $unit == $to_unit
if ($unit !== $to_unit) return false;
// Calculate how many decimals we need ($rp)
// Calculations will always be carried to the decimal; this is
// a limitation with BC (we can't set the scale to be negative)
$new_log = (int) floor(log(abs($n), 10));
$rp = $sigfigs - $new_log - 1;
$neg = $n < 0 ? '-' : '';
// Useful for debugging:
//echo "<pre>n";
//echo "$n\nsigfigs = $sigfigs\nnew_log = $new_log\nlog = $log\nrp = $rp\n</pre>\n";
if ($rp >= 0) {
$n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1);
$n = bcdiv($n, '1', $rp);
} else {
if ($new_log + 1 >= $sigfigs) {
$n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs));
$n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log + 1 - $sigfigs);
}
}
$n = $this->round($n, $sigfigs);
if (strpos($n, '.') !== false) $n = rtrim($n, '0');
$n = rtrim($n, '.');
@@ -189,4 +180,59 @@ class HTMLPurifier_UnitConverter
return $sigfigs;
}
/**
* Adds two numbers, using arbitrary precision when available.
*/
private function add($s1, $s2, $scale) {
if ($this->bcmath) return bcadd($s1, $s2, $scale);
else return $this->scale($s1 + $s2, $scale);
}
/**
* Multiples two numbers, using arbitrary precision when available.
*/
private function mul($s1, $s2, $scale) {
if ($this->bcmath) return bcmul($s1, $s2, $scale);
else return $this->scale($s1 * $s2, $scale);
}
/**
* Divides two numbers, using arbitrary precision when available.
*/
private function div($s1, $s2, $scale) {
if ($this->bcmath) return bcdiv($s1, $s2, $scale);
else return $this->scale($s1 / $s2, $scale);
}
/**
* Rounds a number according to the number of sigfigs it should have,
* using arbitrary precision when available.
*/
private function round($n, $sigfigs) {
$new_log = (int) floor(log(abs($n), 10)); // Number of digits left of decimal - 1
$rp = $sigfigs - $new_log - 1; // Number of decimal places needed
$neg = $n < 0 ? '-' : ''; // Negative sign
if ($this->bcmath) {
if ($rp >= 0) {
$n = bcadd($n, $neg . '0.' . str_repeat('0', $rp) . '5', $rp + 1);
$n = bcdiv($n, '1', $rp);
} else {
// This algorithm partially depends on the standardized
// form of numbers that comes out of bcmath.
$n = bcadd($n, $neg . '5' . str_repeat('0', $new_log - $sigfigs), 0);
$n = substr($n, 0, $sigfigs + strlen($neg)) . str_repeat('0', $new_log - $sigfigs + 1);
}
return $n;
} else {
return $this->scale(round($n, $sigfigs - $new_log - 1), $rp + 1);
}
}
/**
* Scales a float to $scale digits right of decimal point, like BCMath.
*/
private function scale($r, $scale) {
return sprintf('%.' . $scale . 'f', (float) $r);
}
}