Converting Hex String To Float - php

Question

Hi I need to convert this HEX String 6BE15C3E into a float. I have been using an Arduino to do this in the past and below is the code I would use to convert the HEX into a float on an Arduino.
uint8_t l[] = {0x6b, 0xe1, 0x5c, 0x3e};
float var1;
memcpy(&var1, l, 4);
Serial.println(var1);
The result of the above code is 0.22 which is correct. I've tried using the following code in PHP but I don't get the correct answer:
print_r(hex2float("6BE15C3E"));
function hex2float($strHex) {
$hex = sscanf($strHex, "%02x%02x%02x%02x%02x%02x%02x%02x");
$hex = array_reverse($hex);
$bin = implode('', array_map('chr', $hex));
$array = unpack("dnum", $bin);
return $array['num'];
}
This code is returning 4.56588239954E+211 which seems way off and I'm not sure why. I know the Arduino example has been converted into bytes before hand but I don't know if this needs to be done in PHP.

Answer 1

These are probably not optimal, but I think they work:
function hex2float($strHex) {
$hex = sscanf($strHex, "%02x%02x%02x%02x");
$hex = array_reverse($hex);
$bin = implode('', array_map('chr', $hex));
$array = unpack("f", $bin);
return $array[1];
}
function float2hex($f)
{
$a = unpack("I", pack( "f", $f ));
$w = pack("N", $a[1] );
return bin2hex($w);
}
Tests:
function Test($hex)
{
$f = hex2float($hex);
$hex2 = float2hex($f);
echo "$hex --> $f --> $hex2<br>\n";
}
3f800000 --> 1 --> 3f800000
40000000 --> 2 --> 40000000
bf800000 --> -1 --> bf800000
c0000000 --> -2 --> c0000000
6BE15C3E --> 5.448878216557E+26 --> 6be15c3e
3E5CE16B --> 0.21570365130901 --> 3e5ce16b
Assuming your Arduino and your PHP script are running on different "endian" machines, then the array_reverse() should be removed from hex2float to 'fix' that function. (And float2hex will need some kind of reverse to make it match.)
I have not thought through what it would take to implement conversion between DOUBLE and hex.

Answer 2

Thank you Nigel Ren for fixing this issue. Here is the code used to fix the issue:
function hex2float($strHex) {
$hex = sscanf($strHex, "%02x%02x%02x%02x%02x%02x%02x%02x");
$bin = implode('', array_map('chr', $hex));
$array = unpack("f", $bin);
return $array[1];
}
When inputting 6BE15C3E it returns 0.215... which is the correct answer when rounded up.