/**
* @brief Apply the git delta $delta to the byte sequence $base.
*
* @param $delta (string) the delta to apply
* @param $base (string) the sequence to patch
* @returns (string) the patched byte sequence
*/
protected function applyDelta($delta, $base)
{
$pos = 0;
$base_size = Binary::git_varint($delta, &$pos);
$result_size = Binary::git_varint($delta, &$pos);
$r = '';
while ($pos < strlen($delta)) {
$opcode = ord($delta[$pos++]);
if ($opcode & 0x80) {
/* copy a part of $base */
$off = 0;
if ($opcode & 0x1) {
$off = ord($delta[$pos++]);
}
if ($opcode & 0x2) {
$off |= ord($delta[$pos++]) << 8;
}
if ($opcode & 0x4) {
$off |= ord($delta[$pos++]) << 16;
}
if ($opcode & 0x8) {
$off |= ord($delta[$pos++]) << 24;
}
$len = 0;
if ($opcode & 0x10) {
$len = ord($delta[$pos++]);
}
if ($opcode & 0x20) {
$len |= ord($delta[$pos++]) << 8;
}
if ($opcode & 0x40) {
$len |= ord($delta[$pos++]) << 16;
}
$r .= substr($base, $off, $len);
} else {
/* take the next $opcode bytes as they are */
$r .= substr($delta, $pos, $opcode);
$pos += $opcode;
}
}
return $r;
}
