4 bytes to float

[KenHorse]

Take the following 4 bytes, stored in the order shown:

0, 0, 220, 66

The above bytes represent the number 11000, stored as (from the compiler I use for embedded processor work) as a "single", which they define as a "signed 32 bit binary number". I take that to be the same as a float?

How can I convert these 4 bytes to their actual value of 11000? (I've tried pack with no success)

[ginerjm]

What base is this number?

[requinix]

No, it is not the same - read up on what "single" and "double" are. However sometimes people say "float" when they really mean "single".

 

Are you sure that's 11000 and not, say, 110? Because I think it's supposed to be 110.

 

And pack() is the wrong one. That encodes to binary. You want unpack() to decode from binary. Probably using 'g'.

[gizmola]

I have to agree with Requinix, something doesn't add up here. Let's assume that this number is as you described. It would be reasonable to surmise that it's in IEEE 754 format.

 

Given your byte series, here's some code to test:

 

// Bytes of 0,0,220,66
$bin = "\x00\x00\xDC\x42";
$a = unpack('f', $bin);
echo $a[1]; // 110

 

See https://3v4l.org/Mp2Fu

[KenHorse]

Sorry, yes..the value in those bytes should represent 110.0 (sorry, somewhat new to PHP and I inherited a file that I'm working my way though. Obviously I missed a few things along the way....

 

Those 4 bytes are actually read in - line by line -  from a file. This file contains roughly 4,000 lines and format is:

 

1,0

2,0

3,220

4,66

 

So and so forth...

 

Here is how I'm reading (and processing) this file

<?php

$myfile = fopen("myfile.dat", "r") or die("Unable to open file!");

while(!feof($myfile)) {

$indata = fgets($myfile);	
	$position = strpos($indata,","); 
	$buffer1 = intval(trim(substr($indata, $position + 1)));	
	$indata = fgets($myfile);	
	$position = strpos($indata,","); 
	$buffer2 = intval(trim(substr($indata, $position + 1)));	
	$indata = fgets($myfile);	
	$position = strpos($indata,","); 
	$buffer3 = intval(trim(substr($indata, $position + 1)));	
	$indata = fgets($myfile);	
	$position = strpos($indata,","); 
	$buffer4 = intval(trim(substr($indata, $position + 1)));

}
?>

Edited June 28, 2017 by KenHorse

[Jacques1]

Um, what?

 

Your original example had a comma-separated list of four numbers per line. Now you suddenly have four lines with two numbers each.

 

I think we had more than enough confusion. What is the actual format? Not the one you've made up for this forum. The real file format.

[KenHorse]

The file contains 4,096 lines, each one representing 1 byte of data in the EEPROM of an embedded processor. The format of the file is the memory location in decimal, a comma and the value of that EEPROM location. The actual locations of the 4 bytes in question are below but that really shouldn't matter to this issue

 

283,0

284,0

285,220

286,66

Edited June 28, 2017 by KenHorse

[requinix]

So each line has a line number and the byte value?

 

Take your four $buffer variables, convert them to characters, concatenate them all into a string in the order 1234, then unpack() with 'f'.

[gizmola]

Here's a more modern, simpler and cleaner way of approaching this, that incorporates the advice already provided

 

<?php

$file = new SplFileObject("myfile.dat");

$raw = '';
while (!$file->eof()) {
    // Get one line from the file.
    $values = explode(',', $file->fgets());
    $raw .= chr($values[1]);

    // Is this the 4th value?
    if (0 == $values % 4) {
        // Do whatever you need with the value. Just echoed it here
        echo unpack('f', $raw);
        $raw = '';
    }
}

// Unset the file to close the file handle.
$file = null;

[KenHorse]

Thanks all who responded and especially requinix and gizmola. Both of these solutions worked (or perhaps I should say either of them do).

Edited June 28, 2017 by KenHorse