kevinko
commented
8 years ago Hi,
The typical way would be to use the hash.Hash64 (or RollingHash if you need rolling windows) interface in either rabin.go or rabin64.go. RabinFingerprintFixed performs things the long-way using polynomial division and was just used for comparing results. However, results should be identical. What are you using for EMPTY64 in your java code? Results will depend on the chosen irreducible polynomial.
On Sun, Oct 25, 2015 at 4:24 PM, Alexandra notifications@github.com wrote:
I need to generate a Rabin fingerprint for an avro schema so that it can be decoded by a Java application. I used the method RabinFingerprintFixed for generating a fingerprint of a JSON string converted to bytes. However the resulting value is different than the one generated by a method in the avro Java library. Here is the Java code used for generating a fingerprint. Unfortunately I am not so fit in understanding how the algorithm works as to understand if the Go library and the Java library are doing the same thing. Perhaps I am using the wrong method? I would really appreciate your help because I am pretty stuck!
public static long fingerprint64(byte[] data) { long result = EMPTY64; for (byte b: data) result = (result >>> 8) ^ FP64.FP_TABLE[(int)(result ^ b) & 0xff]; return result; } /* An inner class ensures that FP_TABLE initialized only when needed. */ private static class FP64 { private static final long[] FP_TABLE = new long[256]; static { for (int i = 0; i < 256; i++) { long fp = i; for (int j = 0; j < 8; j++) { long mask = -(fp & 1L); fp = (fp >>> 1) ^ (EMPTY64 & mask); } FP_TABLE[i] = fp; } } }
— Reply to this email directly or view it on GitHub https://github.com/kevinko/rabin/issues/2.
astrekalova
I need to generate a Rabin fingerprint for an avro schema so that it can be decoded by a Java application. I used the method RabinFingerprintFixed for generating a fingerprint of a JSON string converted to bytes. However the resulting value is different than the one generated by a method in the avro Java library. Here is the Java code used for generating a fingerprint. Unfortunately I am not so fit in understanding how the algorithm works as to understand if the Go library and the Java library are doing the same thing. Perhaps I am using the wrong method? I would really appreciate your help because I am pretty stuck!
public static long fingerprint64(byte[] data) { long result = EMPTY64; for (byte b: data) result = (result >>> 8) ^ FP64.FP_TABLE[(int)(result ^ b) & 0xff]; return result; } /* An inner class ensures that FP_TABLE initialized only when needed. */ private static class FP64 { private static final long[] FP_TABLE = new long[256]; static { for (int i = 0; i < 256; i++) { long fp = i; for (int j = 0; j < 8; j++) { long mask = -(fp & 1L); fp = (fp >>> 1) ^ (EMPTY64 & mask); } FP_TABLE[i] = fp; } } }
And this is how I generate a fingerprint: file, err := ioutil.ReadFile("ads_raw_bid_stream_request.avsc") var fingerprint = rabin.RabinFingerprintFixed(file)