Convert float to array of bytes in PHP

Question

I need to convert a float value into 4 bytes.

In javascript I usually do it with this code:

  var farr = new Float32Array(1);
  farr[0] = 26.75;
  var barr = new Int8Array(farr.buffer);
  console.log(barr[0]+","+barr[1]+","+barr[2]+","+barr[3]); 
  //26.75 => 0,0,-42,65
  //26.85 => -51,-52,-42,65

I want to do it in php instead of javascript. I it possible?

And here is vice versa enter link description here

Syed Azhar Abbas
– Syed Azhar Abbas

2019-06-27 08:08:18 +00:00
Commented Jun 27, 2019 at 8:08 — Syed Azhar Abbas
– Syed Azhar Abbas, Commented Jun 27, 2019 at 8:08

rvandoni · Accepted Answer · 2015-11-17 13:41:23Z

3

try to use pack and unpack function:

$f = 26.75;
$ar = unpack("c*", pack("f", $f));

print_r($ar);

Result:

Array
(
  [1] => 0
  [2] => 0
  [3] => -42
  [4] => 65
)

you can find a snippet here

edited Nov 17, 2015 at 13:41

answered Nov 17, 2015 at 9:16

rvandoni

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5 Comments

Biribu Over a year ago

Thanks but I don't get the same values with this code as I got with javascript. It you try my 2 examples, values now are differents: 26.85 gives 205 204 222 65

Ferrybig Over a year ago

@Biribu 205 - 256 = 51, same for other numbers, you should subtract the numbers by 256 if they are larger then 128 to compensate for php not giving the number signed (or javascript giving the number unsigned)

Biribu Over a year ago

Perfect. Thanks both.

Alex Blex Over a year ago

@Biribu, just use signed char 'c': unpack("c*", pack("f", $f));

Sprinterfreak Over a year ago

For a ModBus float representation You have to use 'v*':unpack("v*", pack("f", $f)); This results in a two register little endianed uint16 "float"

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