Improve floating point scaling in UnitConverter.

When precision dictates that a number be zero padded, we cannot give sprintf()
a negative precision specifier.  This commit implements manual negative precision
printing of floats, taking into account common rounding errors with floating
point numbers.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

NEWS

@@ -66,6 +66,8 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
   throw an exception when MaintainLineNumbers is true, but a non-tracksLineNumbers
   is being used.
 - Detect if domxml extension is loaded, and use DirectLEx accordingly.
+- Improve handling of big numbers with floating point arithmetic in UnitConverter.
+  Reported by David Morton.
 . Strategy_MakeWellFormed now operates in-place, saving memory and allowing
   for more interesting filter-backtracking
 . New HTMLPurifier_Injector->rewind() functionality, allows injectors to rewind

library/HTMLPurifier/UnitConverter.php

@@ -234,6 +234,18 @@ class HTMLPurifier_UnitConverter
      * Scales a float to $scale digits right of decimal point, like BCMath.
      */
     private function scale($r, $scale) {
+        if ($scale < 0) {
+            // The f sprintf type doesn't support negative numbers, so we
+            // need to cludge things manually. First get the string.
+            $r = sprintf('%.0f', (float) $r);
+            // Due to floating point precision loss, $r will more than likely
+            // look something like 4652999999999.9234. We grab one more digit
+            // than we need to precise from $r and then use that to round
+            // appropriately.
+            $precise = (string) round(substr($r, 0, strlen($r) + $scale), -1);
+            // Now we return it, truncating the zero that was rounded off.
+            return substr($precise, 0, -1) . str_repeat('0', -$scale + 1);
+        }
         return sprintf('%.' . $scale . 'f', (float) $r);
     }
     

tests/HTMLPurifier/UnitConverterTest.php

@@ -94,6 +94,10 @@ class HTMLPurifier_UnitConverterTest extends HTMLPurifier_Harness
         $this->assertConversion('11.112pt', '0.15433in');
     }
     
+    function __onlytestRoundingBigNumber() {
+        $this->assertConversion('444400000000000000000000in', '42660000000000000000000000px');
+    }
+    
     protected function assertSigFig($n, $sigfigs) {
         $converter = new HTMLPurifier_UnitConverter();
         $result = $converter->getSigFigs($n);

tests/index.php

@@ -39,6 +39,7 @@ $AC['file'] = '';
 $AC['xml']  = false;
 $AC['dry']  = false;
 $AC['php']  = $php;
+$AC['help'] = false;
 
 $AC['type'] = '';
 $AC['disable-phpt'] = false;
@@ -46,12 +47,28 @@ $AC['only-phpt'] = false; // alias for --type=phpt
 
 $aliases = array(
     'f' => 'file',
+    'h' => 'help'
 );
 
 // It's important that this does not call the autoloader. Not a problem
 // with a function, but could be if we put this in a class.
 htmlpurifier_parse_args($AC, $aliases);
 
+if ($AC['help']) {
+?>HTML Purifier test suite
+Allowed options:
+    --flush
+    --standalone
+    --file (-f) HTMLPurifier/NameOfTest.php
+    --xml
+    --dry
+    --php /path/to/php
+    --type ( htmlpurifier | configdoc | fstools | htmlt | vtest | phpt )
+    --disable-phpt
+<?php
+    exit;
+}
+
 // Disable PHPT tests if they're not enabled
 if (!$GLOBALS['HTMLPurifierTest']['PHPT']) {
     $AC['disable-phpt'] = true;