zeroshade commented on a change in pull request #11146:
URL: https://github.com/apache/arrow/pull/11146#discussion_r725208507
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File path: go/parquet/internal/bmi/bmi.go
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@@ -254,7 +254,7 @@ func extractBitsGo(bitmap, selectBitmap uint64) uint64 {
for selectBitmap != 0 {
maskLen := bits.OnesCount32(uint32(selectBitmap & lookupMask))
value := pextTable[selectBitmap&lookupMask][bitmap&lookupMask]
- bitValue |= uint64(value << bitLen)
+ bitValue |= uint64(value) << bitLen
Review comment:
this was needed because of the way Go handles types. Because value was a
uint8, it was shifting according to `bitLen` *before* it casted to a uint64 so
the result was incorrect since if `bitLen` was more than 8 it just became 0.
Casting to a uint64 before shifting was necessary. I'm not sure if C++ will
promote value before the shift correctly or if it has the same bug.
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