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process: fix two overflow cases in SourceMap VLQ decoding #31490

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process: fix two overflow cases in SourceMap VLQ decoding #31490

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ec03394
process: fix two overflow cases in SourceMap VLQ decoding
jridgewell Jan 24, 2020
78e7088
process: add tests for SourceMap's decodeVLQ
jridgewell Jan 25, 2020
9d83dbd
process: avoid 0x80000000
jridgewell Jan 25, 2020
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16 changes: 14 additions & 2 deletions lib/internal/source_map/source_map.js
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Original file line number Diff line number Diff line change
Expand Up @@ -303,8 +303,20 @@ function decodeVLQ(stringCharIterator) {

// Fix the sign.
const negative = result & 1;
result >>= 1;
return negative ? -result : result;
// Use unsigned right shift, so that the 32nd bit is properly shifted to the
// 31st, and the 32nd becomes unset.
result >>>= 1;
if (!negative) {
return result;
}

// We need to OR 0x80000000 here to ensure the 32nd bit (the sign bit in a
// 32bit int) is always set for negative numbers. If `result` were 1,
// (meaning `negate` is true and all other bits were zeros), `result` would
// now be 0. But -0 doesn't flip the 32nd bit as intended. All other numbers
// will successfully set the 32nd bit without issue, so doing this is a noop
// for them.
return -result | 0x80000000;
}

/**
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