[CODEC-269] Allow repeat calls to IncrementalHash32.end() to generate the same value.

• Type: Bug
• Status: Resolved
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 1.13
• Fix Version/s: 1.14
• Assignee: Alex Herbert
• Reporter: Alex Herbert
• Created: 21/Nov/19 14:01
• Updated: 21/Nov/19 15:56
• Resolved: 21/Nov/19 15:56

Description

The MurmurHash3.IncrementalHash32 end() method alters the current state of the running hash. Thus if called twice it returns different numbers.

This can be fixed using:

public final int end() {
    // Allow calling end() again after adding no data to return the same result.
    int result = hash;
    // ************
    // Note: This fails to apply masking using 0xff to the 3 remaining bytes.
    // ************
    int k1 = 0;
    switch (unprocessedLength) {
    case 3:
        k1 ^= unprocessed[2] << 16;
    case 2:
        k1 ^= unprocessed[1] << 8;
    case 1:
        k1 ^= unprocessed[0];

        // mix functions
        k1 *= C1_32;
        k1 = Integer.rotateLeft(k1, R1_32);
        k1 *= C2_32;
        result ^= k1;
    }

    // finalization
    result ^= totalLen;
    return fmix32(result);
}