PHP Code to Convert Unsigned Word (Double Byte, 16-bit String) to Signed Integer

This is useful when one tries to read a two 8-bit unsigned char from binary file and then convert to a signed integer.

The following function is good to convert from 2 character byte string such as 0A, FE, etc., to a signed integer (tested working on both 32-bit and 64-bit Windows 7 IIS environment):

function read_short($s) {  // assume $s is an array of (char 1, char 2)



 $temp = (($s[0]&0x00ff)<<8) + ($s[1]&0x00ff);



 if ($temp & (1 << 15) ) { 

  $temp = ($temp - (1 << 16));  // fill all bits with 1 from bit 17 onwards

 }



 return $temp;

}

This is the trick to process your 16-bit char (two unsigned char) in 32-bit/64-bit windows PHP environment.