Php pack: data type issues and validating my results
I am a PHP beginner and my job is to create commands that will later be sent over UDP to a device. Startup: OSX, PHP 5.5.3.8 To create the binary data, I use "pack". Here's an example of my code:
<?php
$in_1 = 0x3100;
$in_2 = 0031;
echo "Inputs: " . $in_1 . "\t" . $in_2;
$bin = pack("v*", $in_1, $in_2);
echo "\nlength: ". strlen($bin);
printf ("\npacked result: %x \n",$bin);
printf("HEX result %h\n", $bin);
file_put_contents("ausgabe.log", $bin, FILE_APPEND);
?>
output in my terminal:
Inputs: 12544 25
length: 4
packed result: 0
HEX result
I wonder about the number 25 for $ in_2. If I assign 0x0031 to $ in_2, the result is 49. What's wrong here?
BTW: My ultimate goal is to build binary instructions that are 12 bytes in a schema like this (decimal values as comments on each line):
function set_routing_item ($in_ch, $out_ch, $on_off, $seq)
{
$command = toggle_two_bytes(37); // 37 --> 0x2500
$status = 0x0000; // 0 --> 0x0000
$pos = 4; // 4= route item
$channel_1 = $in_ch; // 3
$channel_2 = $out_ch; // 6
$preset_no = 0xff; // 255
$value = $on_off; // 33145
$seq = $seq; // 35
// implement building of command using pack here
}
The result in this case (hexadecimal) should look like this: 25 00 00 00 04 03 06 FF 79 81 23 00
Thank!
source to share
I came up with this, but not the best way to do it, correct bitwise operations will be faster.
I am using sprintf
with a format specifier %x
that converts the value to a hex value.
Each conversion specification consists of a percent sign (%)
You will see that I am using %02x
and%04x
-
0
- left button with zeros -
2
or4
- Width, the minimum number of characters to print. In the meantime, there is no need to know about it. ” -
x
- Specifier for hexadecimal, usex
for uppercase.
code:
<?php
function toggle_two_bytes ($two_bytes)
{
$two_bytes = $two_bytes & 0xffff; // limit size to 2 Bytes
$high = ($two_bytes << 8); // bit shift
$low = ($two_bytes >> 8);
$ret = ($high | $low); // OR
$ret = $ret & 0xffff; // limit (again) to two bytes
return ($ret);
}
function set_routing_item ($in_ch, $out_ch, $on_off, $seq)
{
$str = '';
$command = toggle_two_bytes(37);
$str .= sprintf('%04X', $command);
$status = 0x0000;
$str .= sprintf('%04X', $status);
$pos = 4;
$str .= sprintf('%02X', $pos);
$str .= sprintf('%02X', $in_ch);
$str .= sprintf('%02X', $out_ch);
$preset_no = 0xFF;
$str .= sprintf('%02X', $preset_no);
$value = toggle_two_bytes($on_off);
$str .= sprintf('%04X', $value);
$seq = toggle_two_bytes($seq);
$str .= sprintf('%04X', $seq);
for ($i = 0; $i < strlen($str) - 1; $i += 2) {
echo $str[$i] . $str[$i+1] . ' ';
}
}
echo set_routing_item(3, 6, 33145, 35) . PHP_EOL;
Output:
25 00 00 00 04 03 06 FF 79 81 23 00
Demo: https://eval.in/793695
source to share
Sorry for my poor formatted answer. Here is the requested code:
// toggle higher and lower byte of a two-byte short variable
function toggle_two_bytes ($two_bytes)`
{
$two_bytes = $two_bytes & 0xffff; // limit size to 2 Bytes
$high = ($two_bytes << 8); // bit shift
$low = ($two_bytes >> 8);
$ret = ($high | $low); // OR
$ret = $ret & 0xffff; // limit (again) to two bytes
return ($ret);
}
I found out that with package ('v', ...) this is no longer needed.
source to share