Trying to do VLQ Base64 decoding of a LESS source map and getting odd results - source-maps

Question

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Here is a single source mapped line from my .css.map file: 'AILJ,CAAC,GAAgB,CAAC,EAAe,CAAC'
When I try to decode it, I'm getting negative numbers.
class VLQDecoder {
public $charToInt = [];
function __construct() {
foreach (str_split('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=') as $i => $char) {
$this->charToInt[ $char ] = $i;
}
}
public function uRShift(int $a, int $b): int {
if ($b == 0) {
return $a;
}
return ($a >> $b) & ~(1 << (8 * PHP_INT_SIZE - 1) >> ($b - 1));
}
public function segmentToArray(string $segment): array {
$result = [];
$shift = 0;
$value = 0;
foreach (str_split($segment) as $char) {
$integer = $this->charToInt[ $char ];
$has_continuation_bit = $integer & 32;
$integer = $integer & 31;
$value += $integer << $shift;
if ($has_continuation_bit) {
$shift += 5;
} else {
$should_negate = $value & 1;
$value = $this->uRShift($value, 1);
if ($should_negate) {
$result[] = $value === 0 ? - 0x80000000 : $value * - 1;
} else {
$result[] = $value;
}
$value = $shift = 0;
}
}
return $result;
}
}
$VLQDecoder = new VLQDecoder();
$mappings = ['AILJ,CAAC,GAAgB,CAAC,EAAe,CAAC'];
foreach ($mappings as $mapping) {
$segments = array_filter(explode(',', $mapping));
foreach ($segments as $segment) {
$array = $VLQDecoder->segmentToArray($segment);
var_dump([$segment=>$array]);
}
}
This outputs:
array(1) {
["AILJ"]=>
array(4) {
[0]=>
int(0)
[1]=>
int(4)
[2]=>
int(-5)
[3]=>
int(-4)
}
}
array(1) {
["CAAC"]=>
array(4) {
[0]=>
int(1)
[1]=>
int(0)
[2]=>
int(0)
[3]=>
int(1)
}
}
array(1) {
["GAAgB"]=>
array(4) {
[0]=>
int(3)
[1]=>
int(0)
[2]=>
int(0)
[3]=>
int(16)
}
}
array(1) {
["CAAC"]=>
array(4) {
[0]=>
int(1)
[1]=>
int(0)
[2]=>
int(0)
[3]=>
int(1)
}
}
array(1) {
["EAAe"]=>
array(4) {
[0]=>
int(2)
[1]=>
int(0)
[2]=>
int(0)
[3]=>
int(15)
}
}
array(1) {
["CAAC"]=>
array(4) {
[0]=>
int(1)
[1]=>
int(0)
[2]=>
int(0)
[3]=>
int(1)
}
}
The first segment has negative numbers for the row and column indexes. How is this possible?
I also don't see how any value higher than 64 is going to come out of this, yet I have hundreds of CSS files in my source map. How does that work?