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fix(encoding/ghash): PJW64 should use 64-bit width #4728

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fix(encoding/ghash): PJW64 should use 64-bit width #4728

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2 changes: 1 addition & 1 deletion encoding/ghash/ghash_pjw.go
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ func PJW(str []byte) uint32 {
// PJW64 implements the classic PJW hash algorithm for 64 bits.
func PJW64(str []byte) uint64 {
var (
BitsInUnsignedInt uint64 = 32 // 4 * 8
BitsInUnsignedInt uint64 = 64 // 4 * 8

Copilot AI Mar 3, 2026

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This fix changes the hash algorithm's computation, which means PJW64 will now produce a different output for the same input compared to before. The existing unit test in ghash_z_unit_test.go (line 79) still asserts the old expected value of uint64(31150), which was computed using the incorrect 32-bit-wide parameters. The test expected value must be updated to the new correct output produced by the 64-bit algorithm, otherwise the test suite will fail.

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Copilot AI Mar 3, 2026

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The inline comment // 4 * 8 on the BitsInUnsignedInt line is now stale. The value was changed to 64 to correctly represent a 64-bit integer (8 bytes × 8 bits), so the comment should be updated to // 8 * 8 to remain accurate.

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BitsInUnsignedInt uint64 = 64 // 4 * 8
BitsInUnsignedInt uint64 = 64 // 8 * 8

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ThreeQuarters = (BitsInUnsignedInt * 3) / 4
OneEighth = BitsInUnsignedInt / 8
HighBits uint64 = (0xFFFFFFFFFFFFFFFF) << (BitsInUnsignedInt - OneEighth)
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