<?php
// from unpack('H*', file_get_contents("Char.d2s")) for 3v4l.org to read d2s file here
$data = hex2bin('55aa55aa60000000f1060000b5bc59b300000000536f72630000000000000000000000002400000001103863000000003cc7ae62ffffffffffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff0000ffff000000000000570300000000000000000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff8000005e3e9b11000000008888d5f80100000035b70300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000576f6f21060000002a0101000190fd9ffe9ffd9ffe9ffd9f0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000057530100000050000201ffffffff7f00000000000000000000000000000000000201ffffffff7f00000000000000000000000000000000000201ffffffff7f0000000000000000000000000000000000017734002e000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000067660028083082000a06644000b10252067094c1018082800020292400480a0a0030c202008cc060dcc0f0ca3afa160a0000e03f696600000000000000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000004a4d32004a4d100082006500069226160382af144fb080e03f4a4d1000820065000a9226260302791c00c480e03f4a4d10008000654415c076c606821c7ffff58080010a06fe034a4d1000800065008013268303827e82896086dccb000066c5bcfeffff014a4d1000820065000022f6860782b067b7ec80e03f4a4d1000820065001a922636038249b154da80a025040000c07f4a4d1000a0006500a442665363034a4d1000a0006500fe13367703024a4d1000a0006500de13362703024a4d1000a0006500be13361703024a4d1000a00065009e13360703024a4d1000a00065007e1336a707024a4d1000a00065005e13369707024a4d1000a00065003e1336f706024a4d1000a0006500c013e65606024a4d1000a00065006012d68607024a4d1000a00065000e12d60603024a4d1000a00065006412564306024a4d1000800065001e83179303029920441686e03f4a4d1000a0006500fe12d69606024a4d1000a0006500de12d68606024a4d1000a0006500be12d67606024a4d1000a00065009e12e67606024a4d1000a00065007e12e69606024a4d1000a0006500fc13e6a606024a4d1000a0006500dc13c68603024a4d1000a0006500bc13e6b606024a4d1000800065009c83272303826f9aed3186e03f4a4d1000800065007c8317730302acd0c26e86e03f4a4d1000a00065005c13560603024a4d1000a00065003c13569607024a4d1000a00065001c13464603024a4d1000a00065001212d66607024a4d1000a00865001412d66607024a4d1000a0006500fc1226f606024a4d1000a0006500dc12265607024a4d1000a0086500bc12265607024a4d1000a00865009c12265607024a4d1000a00865007c12265607024a4d1000a0086500fa13265607024a4d1000a0006500da43665363034a4d1000a0086500ba43665363034a4d1000a00065009a53468333064a4d10008000650016421616038245fc36c6822cff014a4d100080006500a032166707028c6e88690101000408052c30c0c00054e03f4a4d10008000650411c026c60602385900c78080010a08fe034a4d1000800065004632166707822c1b5e930001000498042c30c0c00054e03f4a4d1000800065007a8337130382a07c2a5786e03f4a4d1008800065000ec326c60602915c92ea8280010a07e23f4a4d100880046500b23237470612e9b107ed80104b83c140fc3776ece0f80f4a4d1000a00065180010365603024a4d00006a664a4d00006b6600');


class D2ByteReader {
    private string $data;
    private int $offset = 0;
    
    public function __construct(string $data){
        if (!$data) return false;
        $this->data = $data;
    }
    
    public function skip(int $numBytes): bool { 
        if ($numBytes < 0 || $numBytes > strlen($this->data)) return false;
        $this->offset += $numBytes;
        return $true;
        
    }
    
    public function seek(int $pos): bool {
        if ($pos < 0 || $pos > strlen($this->data)) return false;
        $this->offset = $pos;
        return true;       
    }
    
    public function read(int $numBytes, bool $str = true){
        $bytes = null;
        for ($i = $this->offset; $i < $this->offset + $numBytes; $i++) {
            $str ? $bytes .= $this->data[$i] : $bytes[] = $this->data[$i];
        }  
        return unpack('H*', $bytes);
    }
    
    public function rewind() : bool {
        $this->offset = 0;
        return true;
    }
    
    public function write8(int $offset, int $byte){
        $this->data[$offset] = pack('C', $byte);
    }
    
    public function writeBytes(int $offset, string $bytes){
        if ($offset < 0 || $offset > strlen($this->data) || $bytes == '') return false;
        $_bytes = str_split($bytes, 2);
        foreach($_bytes as $k => $byte){
            $pos = $offset + $k;
            $this->data[$pos] = pack('H*', $byte);
        }
    }
    public function getData(){
        return $this->data ? $this->data : false;
    }
    public function getOffset(): int {
        return $this->offset;
    }
    
    /*
    @return Byte with Nth bit set to X
    */
    public function setBit(int $byte, int $pos, bool $bit){     
        return ($bit ? ($byte | (1 << $pos)) : ($byte & ~(1 << $pos)) );  
    }
    /*
    @return Bit at Nth position in Byte
    */
    public function getBit(int $byte, int $pos) : int {
        return intval(($byte & (1 << $pos)) != 0);
    }    
}

$c = new D2ByteReader($data);
$c->seek(12);
$checksum = $c->read(4);
var_dump($checksum);
$c->write8(12, 0xFF);
$checksum = $c->read(4);
var_dump($checksum);
$c->writeBytes(12, "FFC0FDA1"); // invalid checksum, but just testing write. Works!
$checksum = $c->read(4);
var_dump($checksum);
$c->writeBytes(12, "b5bc59b3"); // Valid checksum, but just testing write. Works!
$checksum = $c->read(4);
var_dump($checksum);

/* 

Barely any binary functions, all string manipulation on binary files. Working!

To just modify bits in an aligned byte, use setBit();
To just get which bit is set in a byte, use getBit();

To read X arbitary unaligned bits in bytes, 

Seek to offset, 
Read X bytes, 
Convert X bytes to bits,
Reverse bit order in each byte
Load D2BitReader, 
Modify nth Bit, 
Return all bits
Convert to bytes
Reverse bit order in byte
Save bytes

function setBit(int $n, int $p, bool $b){     
    return ($b ? ($n | (1 << $p)) : ($n & ~(1 << $p)) );  
}

function getBit(int $b, int $p){
    return intval(($b & (1 << $p)) != 0);
}

*/