Fix bitwise operation in readUnsignedVarInt

[JuraSciix]

Problem

Method VarInt::readUnsignedLong() works incorrectly due to an bug in C function readUnsignedVarInt.

Description

The method reads the first 4 bytes (while bitwise shift is less than 32), and ignores the rest.
This is happens because of the compiler makes implicit cast of unsigned char to int in bitwise shift operation. An integer value is shifted by7 * 5 (35) bits and more, so it becomes corrupted.

Reproducing

Code using ext-encoding:

<?php

use pmmp\encoding\ByteBuffer;
use pmmp\encoding\VarInt;

$buffer_1 = chr(1 | 0x80) // 1
    . chr(1 | 0x80)       // 2
    . chr(1 | 0x80)       // 3
    . chr(1 | 0x80)       // 4
    . chr(1);             // 5
$buf_1 = new ByteBuffer($buffer_1);
var_dump(VarInt::readUnsignedLong($buf_1));

$buffer_2 = chr(1 | 0x80) // 1
    . chr(1 | 0x80)       // 2
    . chr(1 | 0x80)       // 3
    . chr(1 | 0x80)       // 4
    . chr(1 | 0x80)       // 5
    . chr(1 | 0x80)       // 6
    . chr(1 | 0x80)       // 7
    . chr(1 | 0x80)       // 8
    . chr(1);             // 9
$buf_2 = new ByteBuffer($buffer_2);
var_dump(VarInt::readUnsignedLong($buf_2));

Output:

int(270549121)
int(287458441)

Code using pocketmine/binaryutils:

<?php

use pocketmine\utils\Binary;

$buffer_1 = chr(1 | 0x80) // 1
    . chr(1 | 0x80)       // 2
    . chr(1 | 0x80)       // 3
    . chr(1 | 0x80)       // 4
    . chr(1);             // 5

$offset_1 = 0;
var_dump(Binary::readUnsignedVarLong($buffer_1, $offset_1));

$buffer_2 = chr(1 | 0x80) // 1
    . chr(1 | 0x80)       // 2
    . chr(1 | 0x80)       // 3
    . chr(1 | 0x80)       // 4
    . chr(1 | 0x80)       // 5
    . chr(1 | 0x80)       // 6
    . chr(1 | 0x80)       // 7
    . chr(1 | 0x80)       // 8
    . chr(1);             // 9

$offset_2 = 0;
var_dump(Binary::readUnsignedVarLong($buffer_2, $offset_2));

Output:

int(270549121)
int(72624976668147841)

And the pocketmine/binaryutils result is right, the ext-encoding result is wrong.

Solution

Add explicit cast of unsigned char to type TValue in evaluations with byte variable in readUnsignedVarInt.

[dktapps]

Please add a .phpt test to verify the issue

[JuraSciix]

Added read-varint-unsigned-long.phpt

[dktapps]

Verified locally, this is good to merge once the build passes 👍🏻