note 51271 deleted from language.types.float by bjori
| From: | bjori@php.net | Date: | Thu, 27 Sep 2007 12:32:13 +0000 |
| Subject: | note 51271 deleted from language.types.float by bjori | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-130850@lists.php.net to get a copy of this message | ||
Note Submitter: vic at liveforspeed dot net
----
I couldn't find any function to read a float from a file written by C++ (PC?) for example. This
format has reversed byte order compared to PHP and in addition, there is just no bin2float function
afaik, so I wrote my own binary float 2 usable php float import function.
It does not support SNaN and QNaN values though (didn't need to check for them for my purpose).
Hope it'll be to some use for some:
<?
// $bin must be 4 bytes, MSB first (Most Significant Byte)
function bin2float ($bin) {
$float = (float) 0;
// Read Exponent and Sign (+/-)
$exponent = ord ($bin{3});
if ($sign = $exponent & 128) $exponent -= 128;
$exponent <<= 1;
// Read the remaining bit for Exponent and loop through Mantissa, calculating the Fraction
$fraction = (float) 1;
$div = 1;
for ($x=2; $x>=0; $x--) {
$byte = ord ($bin{$x});
for ($y=7; $y>=0; $y--) {
if ($x==2 && $y==7) {
if ($byte & (1 << $y)) $exponent += 1;
} else {
$div *= 0.5;
if ($byte & (1 << $y)) $fraction += $div;
}
}
}
// 0 value check
if (!$exponent && $fraction == 1) return 0;
// Final calc, returning the converted float
$exponent -= 127;
$float = pow (2, $exponent) * $fraction;
if ($sign) $float = -($float);
return $float;
}
echo bin2float (chr (0xb1).chr (0x5c).chr (0xbc).chr (0x41))."\n";
echo bin2float (chr (0x00).chr (0x18).chr (0x5c).chr (0x3f))."\n";
echo bin2float (chr (0).chr (0).chr (160).chr (193))."\n";
echo bin2float (chr (0).chr (0).chr (0).chr (0));
?>
returns:
23.5452594757
0.859741210938
-20
0
(to understand the workings of floats better, I found http://www.randelshofer.ch/fhw/gri/float.html
to be a good reference)