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Added hamming_distance function

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This commit is contained in:
Andrew Kane
2024-01-23 15:01:11 -08:00
parent c8be3a369b
commit 76c6dbb0a0
6 changed files with 82 additions and 0 deletions
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41
src/vector.c
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@@ -10,6 +10,7 @@
#include "lib/stringinfo.h"
#include "libpq/pqformat.h"
#include "port.h" /* for strtof() */
#include "port/pg_bitutils.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/float.h"
@@ -1134,3 +1135,43 @@ vector_avg(PG_FUNCTION_ARGS)
PG_RETURN_POINTER(result);
}
/*
* Ensure same number of bytes
*/
static inline void
CheckByteLengths(unsigned long aLen, unsigned long bLen)
{
if (aLen != bLen)
ereport(ERROR,
(errcode(ERRCODE_DATA_EXCEPTION),
errmsg("different byte lengths %lu and %lu", aLen, bLen)));
}
/*
* Get the hamming distance between two binary strings
*/
PGDLLEXPORT PG_FUNCTION_INFO_V1(hamming_distance);
Datum
hamming_distance(PG_FUNCTION_ARGS)
{
bytea *a = PG_GETARG_BYTEA_PP(0);
bytea *b = PG_GETARG_BYTEA_PP(1);
char *ax = VARDATA_ANY(a);
char *bx = VARDATA_ANY(b);
unsigned long aLen = VARSIZE_ANY_EXHDR(a);
unsigned long bLen = VARSIZE_ANY_EXHDR(b);
uint64 distance = 0;
CheckByteLengths(aLen, bLen);
for (unsigned long i = 0; i < aLen; i++)
{
unsigned char diff = (unsigned char) (ax[i] ^ bx[i]);
distance += pg_number_of_ones[diff];
}
/* TODO Decide on return type */
PG_RETURN_FLOAT8((double) distance);
}