On Wed, Nov 12, 2014 at 4:54 PM, Peter Geoghegan <p...@heroku.com> wrote:
> Attached patch moves the Levenshtein distance implementation into core.
Oops. Somehow managed to send a *.patch.swp file. :-)
Here is the actual patch.
--
Peter Geoghegan
From b7df918f1a52107637600f3b22d1cff18bd07ae1 Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <p...@heroku.com>
Date: Sat, 30 Nov 2013 23:15:00 -0800
Subject: [PATCH 1/2] Move Levenshtein distance implementation into core
The fuzzystmatch Levenshtein distance implementation is moved from
/contrib to core. However, the related SQL-callable functions may still
only be used with the fuzzystmatch extension installed -- the
fuzzystmatch definitions become simple forwarding stubs.
It is not anticipated that the user-facing SQL functions will be moved
into core in the future, due to the MAX_LEVENSHTEIN_STRLEN restriction.
An in-core Levenshtein distance implementation is only anticipated to be
helpful in building diagnostic messages.
---
contrib/fuzzystrmatch/Makefile | 3 -
contrib/fuzzystrmatch/fuzzystrmatch.c | 81 ++++---
contrib/fuzzystrmatch/levenshtein.c | 403 ----------------------------------
src/backend/utils/adt/Makefile | 2 +
src/backend/utils/adt/levenshtein.c | 394 +++++++++++++++++++++++++++++++++
src/backend/utils/adt/varlena.c | 24 ++
src/include/utils/builtins.h | 5 +
7 files changed, 481 insertions(+), 431 deletions(-)
delete mode 100644 contrib/fuzzystrmatch/levenshtein.c
create mode 100644 src/backend/utils/adt/levenshtein.c
diff --git a/contrib/fuzzystrmatch/Makefile b/contrib/fuzzystrmatch/Makefile
index 024265d..0327d95 100644
--- a/contrib/fuzzystrmatch/Makefile
+++ b/contrib/fuzzystrmatch/Makefile
@@ -17,6 +17,3 @@ top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif
-
-# levenshtein.c is #included by fuzzystrmatch.c
-fuzzystrmatch.o: fuzzystrmatch.c levenshtein.c
diff --git a/contrib/fuzzystrmatch/fuzzystrmatch.c b/contrib/fuzzystrmatch/fuzzystrmatch.c
index 7a53d8a..62e650f 100644
--- a/contrib/fuzzystrmatch/fuzzystrmatch.c
+++ b/contrib/fuzzystrmatch/fuzzystrmatch.c
@@ -154,23 +154,6 @@ getcode(char c)
/* These prevent GH from becoming F */
#define NOGHTOF(c) (getcode(c) & 16) /* BDH */
-/* Faster than memcmp(), for this use case. */
-static inline bool
-rest_of_char_same(const char *s1, const char *s2, int len)
-{
- while (len > 0)
- {
- len--;
- if (s1[len] != s2[len])
- return false;
- }
- return true;
-}
-
-#include "levenshtein.c"
-#define LEVENSHTEIN_LESS_EQUAL
-#include "levenshtein.c"
-
PG_FUNCTION_INFO_V1(levenshtein_with_costs);
Datum
levenshtein_with_costs(PG_FUNCTION_ARGS)
@@ -180,8 +163,20 @@ levenshtein_with_costs(PG_FUNCTION_ARGS)
int ins_c = PG_GETARG_INT32(2);
int del_c = PG_GETARG_INT32(3);
int sub_c = PG_GETARG_INT32(4);
-
- PG_RETURN_INT32(levenshtein_internal(src, dst, ins_c, del_c, sub_c));
+ const char *s_data;
+ const char *t_data;
+ int s_bytes,
+ t_bytes;
+
+ /* Extract a pointer to the actual character data */
+ s_data = VARDATA_ANY(src);
+ t_data = VARDATA_ANY(dst);
+ /* Determine length of each string in bytes and characters */
+ s_bytes = VARSIZE_ANY_EXHDR(src);
+ t_bytes = VARSIZE_ANY_EXHDR(dst);
+
+ PG_RETURN_INT32(varstr_leven(s_data, s_bytes, t_data, t_bytes, ins_c,
+ del_c, sub_c));
}
@@ -191,8 +186,20 @@ levenshtein(PG_FUNCTION_ARGS)
{
text *src = PG_GETARG_TEXT_PP(0);
text *dst = PG_GETARG_TEXT_PP(1);
-
- PG_RETURN_INT32(levenshtein_internal(src, dst, 1, 1, 1));
+ const char *s_data;
+ const char *t_data;
+ int s_bytes,
+ t_bytes;
+
+ /* Extract a pointer to the actual character data */
+ s_data = VARDATA_ANY(src);
+ t_data = VARDATA_ANY(dst);
+ /* Determine length of each string in bytes and characters */
+ s_bytes = VARSIZE_ANY_EXHDR(src);
+ t_bytes = VARSIZE_ANY_EXHDR(dst);
+
+ PG_RETURN_INT32(varstr_leven(s_data, s_bytes, t_data, t_bytes, 1, 1,
+ 1));
}
@@ -206,8 +213,20 @@ levenshtein_less_equal_with_costs(PG_FUNCTION_ARGS)
int del_c = PG_GETARG_INT32(3);
int sub_c = PG_GETARG_INT32(4);
int max_d = PG_GETARG_INT32(5);
-
- PG_RETURN_INT32(levenshtein_less_equal_internal(src, dst, ins_c, del_c, sub_c, max_d));
+ const char *s_data;
+ const char *t_data;
+ int s_bytes,
+ t_bytes;
+
+ /* Extract a pointer to the actual character data */
+ s_data = VARDATA_ANY(src);
+ t_data = VARDATA_ANY(dst);
+ /* Determine length of each string in bytes and characters */
+ s_bytes = VARSIZE_ANY_EXHDR(src);
+ t_bytes = VARSIZE_ANY_EXHDR(dst);
+
+ PG_RETURN_INT32(varstr_leven_less_equal(s_data, s_bytes, t_data, t_bytes,
+ ins_c, del_c, sub_c, max_d));
}
@@ -218,8 +237,20 @@ levenshtein_less_equal(PG_FUNCTION_ARGS)
text *src = PG_GETARG_TEXT_PP(0);
text *dst = PG_GETARG_TEXT_PP(1);
int max_d = PG_GETARG_INT32(2);
-
- PG_RETURN_INT32(levenshtein_less_equal_internal(src, dst, 1, 1, 1, max_d));
+ const char *s_data;
+ const char *t_data;
+ int s_bytes,
+ t_bytes;
+
+ /* Extract a pointer to the actual character data */
+ s_data = VARDATA_ANY(src);
+ t_data = VARDATA_ANY(dst);
+ /* Determine length of each string in bytes and characters */
+ s_bytes = VARSIZE_ANY_EXHDR(src);
+ t_bytes = VARSIZE_ANY_EXHDR(dst);
+
+ PG_RETURN_INT32(varstr_leven_less_equal(s_data, s_bytes, t_data, t_bytes,
+ 1, 1, 1, max_d));
}
diff --git a/contrib/fuzzystrmatch/levenshtein.c b/contrib/fuzzystrmatch/levenshtein.c
deleted file mode 100644
index 4f37a54..0000000
--- a/contrib/fuzzystrmatch/levenshtein.c
+++ /dev/null
@@ -1,403 +0,0 @@
-/*
- * levenshtein.c
- *
- * Functions for "fuzzy" comparison of strings
- *
- * Joe Conway <m...@joeconway.com>
- *
- * Copyright (c) 2001-2014, PostgreSQL Global Development Group
- * ALL RIGHTS RESERVED;
- *
- * levenshtein()
- * -------------
- * Written based on a description of the algorithm by Michael Gilleland
- * found at http://www.merriampark.com/ld.htm
- * Also looked at levenshtein.c in the PHP 4.0.6 distribution for
- * inspiration.
- * Configurable penalty costs extension is introduced by Volkan
- * YAZICI <volkan.yaz...@gmail.com>.
- */
-
-/*
- * External declarations for exported functions
- */
-#ifdef LEVENSHTEIN_LESS_EQUAL
-static int levenshtein_less_equal_internal(text *s, text *t,
- int ins_c, int del_c, int sub_c, int max_d);
-#else
-static int levenshtein_internal(text *s, text *t,
- int ins_c, int del_c, int sub_c);
-#endif
-
-#define MAX_LEVENSHTEIN_STRLEN 255
-
-
-/*
- * Calculates Levenshtein distance metric between supplied strings. Generally
- * (1, 1, 1) penalty costs suffices for common cases, but your mileage may
- * vary.
- *
- * One way to compute Levenshtein distance is to incrementally construct
- * an (m+1)x(n+1) matrix where cell (i, j) represents the minimum number
- * of operations required to transform the first i characters of s into
- * the first j characters of t. The last column of the final row is the
- * answer.
- *
- * We use that algorithm here with some modification. In lieu of holding
- * the entire array in memory at once, we'll just use two arrays of size
- * m+1 for storing accumulated values. At each step one array represents
- * the "previous" row and one is the "current" row of the notional large
- * array.
- *
- * If max_d >= 0, we only need to provide an accurate answer when that answer
- * is less than or equal to the bound. From any cell in the matrix, there is
- * theoretical "minimum residual distance" from that cell to the last column
- * of the final row. This minimum residual distance is zero when the
- * untransformed portions of the strings are of equal length (because we might
- * get lucky and find all the remaining characters matching) and is otherwise
- * based on the minimum number of insertions or deletions needed to make them
- * equal length. The residual distance grows as we move toward the upper
- * right or lower left corners of the matrix. When the max_d bound is
- * usefully tight, we can use this property to avoid computing the entirety
- * of each row; instead, we maintain a start_column and stop_column that
- * identify the portion of the matrix close to the diagonal which can still
- * affect the final answer.
- */
-static int
-#ifdef LEVENSHTEIN_LESS_EQUAL
-levenshtein_less_equal_internal(text *s, text *t,
- int ins_c, int del_c, int sub_c, int max_d)
-#else
-levenshtein_internal(text *s, text *t,
- int ins_c, int del_c, int sub_c)
-#endif
-{
- int m,
- n,
- s_bytes,
- t_bytes;
- int *prev;
- int *curr;
- int *s_char_len = NULL;
- int i,
- j;
- const char *s_data;
- const char *t_data;
- const char *y;
-
- /*
- * For levenshtein_less_equal_internal, we have real variables called
- * start_column and stop_column; otherwise it's just short-hand for 0 and
- * m.
- */
-#ifdef LEVENSHTEIN_LESS_EQUAL
- int start_column,
- stop_column;
-
-#undef START_COLUMN
-#undef STOP_COLUMN
-#define START_COLUMN start_column
-#define STOP_COLUMN stop_column
-#else
-#undef START_COLUMN
-#undef STOP_COLUMN
-#define START_COLUMN 0
-#define STOP_COLUMN m
-#endif
-
- /* Extract a pointer to the actual character data. */
- s_data = VARDATA_ANY(s);
- t_data = VARDATA_ANY(t);
-
- /* Determine length of each string in bytes and characters. */
- s_bytes = VARSIZE_ANY_EXHDR(s);
- t_bytes = VARSIZE_ANY_EXHDR(t);
- m = pg_mbstrlen_with_len(s_data, s_bytes);
- n = pg_mbstrlen_with_len(t_data, t_bytes);
-
- /*
- * We can transform an empty s into t with n insertions, or a non-empty t
- * into an empty s with m deletions.
- */
- if (!m)
- return n * ins_c;
- if (!n)
- return m * del_c;
-
- /*
- * For security concerns, restrict excessive CPU+RAM usage. (This
- * implementation uses O(m) memory and has O(mn) complexity.)
- */
- if (m > MAX_LEVENSHTEIN_STRLEN ||
- n > MAX_LEVENSHTEIN_STRLEN)
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
- errmsg("argument exceeds the maximum length of %d bytes",
- MAX_LEVENSHTEIN_STRLEN)));
-
-#ifdef LEVENSHTEIN_LESS_EQUAL
- /* Initialize start and stop columns. */
- start_column = 0;
- stop_column = m + 1;
-
- /*
- * If max_d >= 0, determine whether the bound is impossibly tight. If so,
- * return max_d + 1 immediately. Otherwise, determine whether it's tight
- * enough to limit the computation we must perform. If so, figure out
- * initial stop column.
- */
- if (max_d >= 0)
- {
- int min_theo_d; /* Theoretical minimum distance. */
- int max_theo_d; /* Theoretical maximum distance. */
- int net_inserts = n - m;
-
- min_theo_d = net_inserts < 0 ?
- -net_inserts * del_c : net_inserts * ins_c;
- if (min_theo_d > max_d)
- return max_d + 1;
- if (ins_c + del_c < sub_c)
- sub_c = ins_c + del_c;
- max_theo_d = min_theo_d + sub_c * Min(m, n);
- if (max_d >= max_theo_d)
- max_d = -1;
- else if (ins_c + del_c > 0)
- {
- /*
- * Figure out how much of the first row of the notional matrix we
- * need to fill in. If the string is growing, the theoretical
- * minimum distance already incorporates the cost of deleting the
- * number of characters necessary to make the two strings equal in
- * length. Each additional deletion forces another insertion, so
- * the best-case total cost increases by ins_c + del_c. If the
- * string is shrinking, the minimum theoretical cost assumes no
- * excess deletions; that is, we're starting no further right than
- * column n - m. If we do start further right, the best-case
- * total cost increases by ins_c + del_c for each move right.
- */
- int slack_d = max_d - min_theo_d;
- int best_column = net_inserts < 0 ? -net_inserts : 0;
-
- stop_column = best_column + (slack_d / (ins_c + del_c)) + 1;
- if (stop_column > m)
- stop_column = m + 1;
- }
- }
-#endif
-
- /*
- * In order to avoid calling pg_mblen() repeatedly on each character in s,
- * we cache all the lengths before starting the main loop -- but if all
- * the characters in both strings are single byte, then we skip this and
- * use a fast-path in the main loop. If only one string contains
- * multi-byte characters, we still build the array, so that the fast-path
- * needn't deal with the case where the array hasn't been initialized.
- */
- if (m != s_bytes || n != t_bytes)
- {
- int i;
- const char *cp = s_data;
-
- s_char_len = (int *) palloc((m + 1) * sizeof(int));
- for (i = 0; i < m; ++i)
- {
- s_char_len[i] = pg_mblen(cp);
- cp += s_char_len[i];
- }
- s_char_len[i] = 0;
- }
-
- /* One more cell for initialization column and row. */
- ++m;
- ++n;
-
- /* Previous and current rows of notional array. */
- prev = (int *) palloc(2 * m * sizeof(int));
- curr = prev + m;
-
- /*
- * To transform the first i characters of s into the first 0 characters of
- * t, we must perform i deletions.
- */
- for (i = START_COLUMN; i < STOP_COLUMN; i++)
- prev[i] = i * del_c;
-
- /* Loop through rows of the notional array */
- for (y = t_data, j = 1; j < n; j++)
- {
- int *temp;
- const char *x = s_data;
- int y_char_len = n != t_bytes + 1 ? pg_mblen(y) : 1;
-
-#ifdef LEVENSHTEIN_LESS_EQUAL
-
- /*
- * In the best case, values percolate down the diagonal unchanged, so
- * we must increment stop_column unless it's already on the right end
- * of the array. The inner loop will read prev[stop_column], so we
- * have to initialize it even though it shouldn't affect the result.
- */
- if (stop_column < m)
- {
- prev[stop_column] = max_d + 1;
- ++stop_column;
- }
-
- /*
- * The main loop fills in curr, but curr[0] needs a special case: to
- * transform the first 0 characters of s into the first j characters
- * of t, we must perform j insertions. However, if start_column > 0,
- * this special case does not apply.
- */
- if (start_column == 0)
- {
- curr[0] = j * ins_c;
- i = 1;
- }
- else
- i = start_column;
-#else
- curr[0] = j * ins_c;
- i = 1;
-#endif
-
- /*
- * This inner loop is critical to performance, so we include a
- * fast-path to handle the (fairly common) case where no multibyte
- * characters are in the mix. The fast-path is entitled to assume
- * that if s_char_len is not initialized then BOTH strings contain
- * only single-byte characters.
- */
- if (s_char_len != NULL)
- {
- for (; i < STOP_COLUMN; i++)
- {
- int ins;
- int del;
- int sub;
- int x_char_len = s_char_len[i - 1];
-
- /*
- * Calculate costs for insertion, deletion, and substitution.
- *
- * When calculating cost for substitution, we compare the last
- * character of each possibly-multibyte character first,
- * because that's enough to rule out most mis-matches. If we
- * get past that test, then we compare the lengths and the
- * remaining bytes.
- */
- ins = prev[i] + ins_c;
- del = curr[i - 1] + del_c;
- if (x[x_char_len - 1] == y[y_char_len - 1]
- && x_char_len == y_char_len &&
- (x_char_len == 1 || rest_of_char_same(x, y, x_char_len)))
- sub = prev[i - 1];
- else
- sub = prev[i - 1] + sub_c;
-
- /* Take the one with minimum cost. */
- curr[i] = Min(ins, del);
- curr[i] = Min(curr[i], sub);
-
- /* Point to next character. */
- x += x_char_len;
- }
- }
- else
- {
- for (; i < STOP_COLUMN; i++)
- {
- int ins;
- int del;
- int sub;
-
- /* Calculate costs for insertion, deletion, and substitution. */
- ins = prev[i] + ins_c;
- del = curr[i - 1] + del_c;
- sub = prev[i - 1] + ((*x == *y) ? 0 : sub_c);
-
- /* Take the one with minimum cost. */
- curr[i] = Min(ins, del);
- curr[i] = Min(curr[i], sub);
-
- /* Point to next character. */
- x++;
- }
- }
-
- /* Swap current row with previous row. */
- temp = curr;
- curr = prev;
- prev = temp;
-
- /* Point to next character. */
- y += y_char_len;
-
-#ifdef LEVENSHTEIN_LESS_EQUAL
-
- /*
- * This chunk of code represents a significant performance hit if used
- * in the case where there is no max_d bound. This is probably not
- * because the max_d >= 0 test itself is expensive, but rather because
- * the possibility of needing to execute this code prevents tight
- * optimization of the loop as a whole.
- */
- if (max_d >= 0)
- {
- /*
- * The "zero point" is the column of the current row where the
- * remaining portions of the strings are of equal length. There
- * are (n - 1) characters in the target string, of which j have
- * been transformed. There are (m - 1) characters in the source
- * string, so we want to find the value for zp where (n - 1) - j =
- * (m - 1) - zp.
- */
- int zp = j - (n - m);
-
- /* Check whether the stop column can slide left. */
- while (stop_column > 0)
- {
- int ii = stop_column - 1;
- int net_inserts = ii - zp;
-
- if (prev[ii] + (net_inserts > 0 ? net_inserts * ins_c :
- -net_inserts * del_c) <= max_d)
- break;
- stop_column--;
- }
-
- /* Check whether the start column can slide right. */
- while (start_column < stop_column)
- {
- int net_inserts = start_column - zp;
-
- if (prev[start_column] +
- (net_inserts > 0 ? net_inserts * ins_c :
- -net_inserts * del_c) <= max_d)
- break;
-
- /*
- * We'll never again update these values, so we must make sure
- * there's nothing here that could confuse any future
- * iteration of the outer loop.
- */
- prev[start_column] = max_d + 1;
- curr[start_column] = max_d + 1;
- if (start_column != 0)
- s_data += (s_char_len != NULL) ? s_char_len[start_column - 1] : 1;
- start_column++;
- }
-
- /* If they cross, we're going to exceed the bound. */
- if (start_column >= stop_column)
- return max_d + 1;
- }
-#endif
- }
-
- /*
- * Because the final value was swapped from the previous row to the
- * current row, that's where we'll find it.
- */
- return prev[m - 1];
-}
diff --git a/src/backend/utils/adt/Makefile b/src/backend/utils/adt/Makefile
index 7b4391b..3ea9bf4 100644
--- a/src/backend/utils/adt/Makefile
+++ b/src/backend/utils/adt/Makefile
@@ -38,4 +38,6 @@ OBJS = acl.o arrayfuncs.o array_selfuncs.o array_typanalyze.o \
like.o: like.c like_match.c
+varlena.o: varlena.c levenshtein.c
+
include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/utils/adt/levenshtein.c b/src/backend/utils/adt/levenshtein.c
new file mode 100644
index 0000000..bf4f1dd
--- /dev/null
+++ b/src/backend/utils/adt/levenshtein.c
@@ -0,0 +1,394 @@
+/*-------------------------------------------------------------------------
+ *
+ * levenshtein.c
+ * Levenshtein distance implementation.
+ *
+ * Original author: Joe Conway <m...@joeconway.com>
+ *
+ * This file is included by varlena.c twice, to provide matching code for (1)
+ * Levenshtein distance with custom costings, and (2) Levenshtein distance with
+ * custom costings and a "max" value above which exact distances are not
+ * interesting. Before the inclusion, we rely on the presence of the inline
+ * function rest_of_char_same().
+ *
+ * Written based on a description of the algorithm by Michael Gilleland found
+ * at http://www.merriampark.com/ld.htm. Also looked at levenshtein.c in the
+ * PHP 4.0.6 distribution for inspiration. Configurable penalty costs
+ * extension is introduced by Volkan YAZICI <volkan.yaz...@gmail.com.
+ *
+ * Copyright (c) 2001-2014, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * src/backend/utils/adt/levenshtein.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#define MAX_LEVENSHTEIN_STRLEN 255
+
+/*
+ * Calculates Levenshtein distance metric between supplied csrings, which are
+ * not necessarily null-terminated. Generally (1, 1, 1) penalty costs suffices
+ * for common cases, but your mileage may vary.
+ *
+ * One way to compute Levenshtein distance is to incrementally construct
+ * an (m+1)x(n+1) matrix where cell (i, j) represents the minimum number
+ * of operations required to transform the first i characters of s into
+ * the first j characters of t. The last column of the final row is the
+ * answer.
+ *
+ * We use that algorithm here with some modification. In lieu of holding
+ * the entire array in memory at once, we'll just use two arrays of size
+ * m+1 for storing accumulated values. At each step one array represents
+ * the "previous" row and one is the "current" row of the notional large
+ * array.
+ *
+ * If max_d >= 0, we only need to provide an accurate answer when that answer
+ * is less than or equal to the bound. From any cell in the matrix, there is
+ * theoretical "minimum residual distance" from that cell to the last column
+ * of the final row. This minimum residual distance is zero when the
+ * untransformed portions of the strings are of equal length (because we might
+ * get lucky and find all the remaining characters matching) and is otherwise
+ * based on the minimum number of insertions or deletions needed to make them
+ * equal length. The residual distance grows as we move toward the upper
+ * right or lower left corners of the matrix. When the max_d bound is
+ * usefully tight, we can use this property to avoid computing the entirety
+ * of each row; instead, we maintain a start_column and stop_column that
+ * identify the portion of the matrix close to the diagonal which can still
+ * affect the final answer.
+ */
+int
+#ifdef LEVENSHTEIN_LESS_EQUAL
+varstr_leven_less_equal(const char *source, int slen, const char *target,
+ int tlen, int ins_c, int del_c, int sub_c, int max_d)
+#else
+varstr_leven(const char *source, int slen, const char *target, int tlen,
+ int ins_c, int del_c, int sub_c)
+#endif
+{
+ int m,
+ n;
+ int *prev;
+ int *curr;
+ int *s_char_len = NULL;
+ int i,
+ j;
+ const char *y;
+
+ /*
+ * For varstr_levenshtein_less_equal, we have real variables called
+ * start_column and stop_column; otherwise it's just short-hand for 0 and
+ * m.
+ */
+#ifdef LEVENSHTEIN_LESS_EQUAL
+ int start_column,
+ stop_column;
+
+#undef START_COLUMN
+#undef STOP_COLUMN
+#define START_COLUMN start_column
+#define STOP_COLUMN stop_column
+#else
+#undef START_COLUMN
+#undef STOP_COLUMN
+#define START_COLUMN 0
+#define STOP_COLUMN m
+#endif
+
+ /*
+ * A common use for Levenshtein distance is to match attributes when
+ * building diagnostic, user-visible messages. Restrict the size of
+ * MAX_LEVENSHTEIN_STRLEN at compile time such that this is guaranteed to
+ * work.
+ */
+ StaticAssertStmt(NAMEDATALEN <= MAX_LEVENSHTEIN_STRLEN,
+ "Levenshtein hinting mechanism restricts NAMEDATALEN");
+
+ m = pg_mbstrlen_with_len(source, slen);
+ n = pg_mbstrlen_with_len(target, tlen);
+
+ /*
+ * We can transform an empty s into t with n insertions, or a non-empty t
+ * into an empty s with m deletions.
+ */
+ if (!m)
+ return n * ins_c;
+ if (!n)
+ return m * del_c;
+
+ /*
+ * For security concerns, restrict excessive CPU+RAM usage. (This
+ * implementation uses O(m) memory and has O(mn) complexity.)
+ */
+ if (m > MAX_LEVENSHTEIN_STRLEN ||
+ n > MAX_LEVENSHTEIN_STRLEN)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("argument exceeds the maximum length of %d bytes",
+ MAX_LEVENSHTEIN_STRLEN)));
+
+#ifdef LEVENSHTEIN_LESS_EQUAL
+ /* Initialize start and stop columns. */
+ start_column = 0;
+ stop_column = m + 1;
+
+ /*
+ * If max_d >= 0, determine whether the bound is impossibly tight. If so,
+ * return max_d + 1 immediately. Otherwise, determine whether it's tight
+ * enough to limit the computation we must perform. If so, figure out
+ * initial stop column.
+ */
+ if (max_d >= 0)
+ {
+ int min_theo_d; /* Theoretical minimum distance. */
+ int max_theo_d; /* Theoretical maximum distance. */
+ int net_inserts = n - m;
+
+ min_theo_d = net_inserts < 0 ?
+ -net_inserts * del_c : net_inserts * ins_c;
+ if (min_theo_d > max_d)
+ return max_d + 1;
+ if (ins_c + del_c < sub_c)
+ sub_c = ins_c + del_c;
+ max_theo_d = min_theo_d + sub_c * Min(m, n);
+ if (max_d >= max_theo_d)
+ max_d = -1;
+ else if (ins_c + del_c > 0)
+ {
+ /*
+ * Figure out how much of the first row of the notional matrix we
+ * need to fill in. If the string is growing, the theoretical
+ * minimum distance already incorporates the cost of deleting the
+ * number of characters necessary to make the two strings equal in
+ * length. Each additional deletion forces another insertion, so
+ * the best-case total cost increases by ins_c + del_c. If the
+ * string is shrinking, the minimum theoretical cost assumes no
+ * excess deletions; that is, we're starting no further right than
+ * column n - m. If we do start further right, the best-case
+ * total cost increases by ins_c + del_c for each move right.
+ */
+ int slack_d = max_d - min_theo_d;
+ int best_column = net_inserts < 0 ? -net_inserts : 0;
+
+ stop_column = best_column + (slack_d / (ins_c + del_c)) + 1;
+ if (stop_column > m)
+ stop_column = m + 1;
+ }
+ }
+#endif
+
+ /*
+ * In order to avoid calling pg_mblen() repeatedly on each character in s,
+ * we cache all the lengths before starting the main loop -- but if all
+ * the characters in both strings are single byte, then we skip this and
+ * use a fast-path in the main loop. If only one string contains
+ * multi-byte characters, we still build the array, so that the fast-path
+ * needn't deal with the case where the array hasn't been initialized.
+ */
+ if (m != slen || n != tlen)
+ {
+ int i;
+ const char *cp = source;
+
+ s_char_len = (int *) palloc((m + 1) * sizeof(int));
+ for (i = 0; i < m; ++i)
+ {
+ s_char_len[i] = pg_mblen(cp);
+ cp += s_char_len[i];
+ }
+ s_char_len[i] = 0;
+ }
+
+ /* One more cell for initialization column and row. */
+ ++m;
+ ++n;
+
+ /* Previous and current rows of notional array. */
+ prev = (int *) palloc(2 * m * sizeof(int));
+ curr = prev + m;
+
+ /*
+ * To transform the first i characters of s into the first 0 characters of
+ * t, we must perform i deletions.
+ */
+ for (i = START_COLUMN; i < STOP_COLUMN; i++)
+ prev[i] = i * del_c;
+
+ /* Loop through rows of the notional array */
+ for (y = target, j = 1; j < n; j++)
+ {
+ int *temp;
+ const char *x = source;
+ int y_char_len = n != tlen + 1 ? pg_mblen(y) : 1;
+
+#ifdef LEVENSHTEIN_LESS_EQUAL
+
+ /*
+ * In the best case, values percolate down the diagonal unchanged, so
+ * we must increment stop_column unless it's already on the right end
+ * of the array. The inner loop will read prev[stop_column], so we
+ * have to initialize it even though it shouldn't affect the result.
+ */
+ if (stop_column < m)
+ {
+ prev[stop_column] = max_d + 1;
+ ++stop_column;
+ }
+
+ /*
+ * The main loop fills in curr, but curr[0] needs a special case: to
+ * transform the first 0 characters of s into the first j characters
+ * of t, we must perform j insertions. However, if start_column > 0,
+ * this special case does not apply.
+ */
+ if (start_column == 0)
+ {
+ curr[0] = j * ins_c;
+ i = 1;
+ }
+ else
+ i = start_column;
+#else
+ curr[0] = j * ins_c;
+ i = 1;
+#endif
+
+ /*
+ * This inner loop is critical to performance, so we include a
+ * fast-path to handle the (fairly common) case where no multibyte
+ * characters are in the mix. The fast-path is entitled to assume
+ * that if s_char_len is not initialized then BOTH strings contain
+ * only single-byte characters.
+ */
+ if (s_char_len != NULL)
+ {
+ for (; i < STOP_COLUMN; i++)
+ {
+ int ins;
+ int del;
+ int sub;
+ int x_char_len = s_char_len[i - 1];
+
+ /*
+ * Calculate costs for insertion, deletion, and substitution.
+ *
+ * When calculating cost for substitution, we compare the last
+ * character of each possibly-multibyte character first,
+ * because that's enough to rule out most mis-matches. If we
+ * get past that test, then we compare the lengths and the
+ * remaining bytes.
+ */
+ ins = prev[i] + ins_c;
+ del = curr[i - 1] + del_c;
+ if (x[x_char_len - 1] == y[y_char_len - 1]
+ && x_char_len == y_char_len &&
+ (x_char_len == 1 || rest_of_char_same(x, y, x_char_len)))
+ sub = prev[i - 1];
+ else
+ sub = prev[i - 1] + sub_c;
+
+ /* Take the one with minimum cost. */
+ curr[i] = Min(ins, del);
+ curr[i] = Min(curr[i], sub);
+
+ /* Point to next character. */
+ x += x_char_len;
+ }
+ }
+ else
+ {
+ for (; i < STOP_COLUMN; i++)
+ {
+ int ins;
+ int del;
+ int sub;
+
+ /* Calculate costs for insertion, deletion, and substitution. */
+ ins = prev[i] + ins_c;
+ del = curr[i - 1] + del_c;
+ sub = prev[i - 1] + ((*x == *y) ? 0 : sub_c);
+
+ /* Take the one with minimum cost. */
+ curr[i] = Min(ins, del);
+ curr[i] = Min(curr[i], sub);
+
+ /* Point to next character. */
+ x++;
+ }
+ }
+
+ /* Swap current row with previous row. */
+ temp = curr;
+ curr = prev;
+ prev = temp;
+
+ /* Point to next character. */
+ y += y_char_len;
+
+#ifdef LEVENSHTEIN_LESS_EQUAL
+
+ /*
+ * This chunk of code represents a significant performance hit if used
+ * in the case where there is no max_d bound. This is probably not
+ * because the max_d >= 0 test itself is expensive, but rather because
+ * the possibility of needing to execute this code prevents tight
+ * optimization of the loop as a whole.
+ */
+ if (max_d >= 0)
+ {
+ /*
+ * The "zero point" is the column of the current row where the
+ * remaining portions of the strings are of equal length. There
+ * are (n - 1) characters in the target string, of which j have
+ * been transformed. There are (m - 1) characters in the source
+ * string, so we want to find the value for zp where (n - 1) - j =
+ * (m - 1) - zp.
+ */
+ int zp = j - (n - m);
+
+ /* Check whether the stop column can slide left. */
+ while (stop_column > 0)
+ {
+ int ii = stop_column - 1;
+ int net_inserts = ii - zp;
+
+ if (prev[ii] + (net_inserts > 0 ? net_inserts * ins_c :
+ -net_inserts * del_c) <= max_d)
+ break;
+ stop_column--;
+ }
+
+ /* Check whether the start column can slide right. */
+ while (start_column < stop_column)
+ {
+ int net_inserts = start_column - zp;
+
+ if (prev[start_column] +
+ (net_inserts > 0 ? net_inserts * ins_c :
+ -net_inserts * del_c) <= max_d)
+ break;
+
+ /*
+ * We'll never again update these values, so we must make sure
+ * there's nothing here that could confuse any future
+ * iteration of the outer loop.
+ */
+ prev[start_column] = max_d + 1;
+ curr[start_column] = max_d + 1;
+ if (start_column != 0)
+ source += (s_char_len != NULL) ? s_char_len[start_column - 1] : 1;
+ start_column++;
+ }
+
+ /* If they cross, we're going to exceed the bound. */
+ if (start_column >= stop_column)
+ return max_d + 1;
+ }
+#endif
+ }
+
+ /*
+ * Because the final value was swapped from the previous row to the
+ * current row, that's where we'll find it.
+ */
+ return prev[m - 1];
+}
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index c3171b5..48afc61 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -1546,6 +1546,30 @@ varstr_cmp(char *arg1, int len1, char *arg2, int len2, Oid collid)
return result;
}
+/*
+ * varstr_leven()
+ * varstr_leven_less_equal()
+ * Levenshtein distance functions. All arguments should be strlen(s) <= 255.
+ * Guaranteed to work with Name datatype's cstrings.
+ * For full details see levenshtein.c.
+ *
+ * Helper function. Faster than memcmp(), for this use case.
+ */
+static inline bool
+rest_of_char_same(const char *s1, const char *s2, int len)
+{
+ while (len > 0)
+ {
+ len--;
+ if (s1[len] != s2[len])
+ return false;
+ }
+ return true;
+}
+/* Expand each Levenshtein distance variant */
+#include "levenshtein.c"
+#define LEVENSHTEIN_LESS_EQUAL
+#include "levenshtein.c"
/* text_cmp()
* Internal comparison function for text strings.
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index 3ba34f8..7298c93 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -786,6 +786,11 @@ extern Datum textoverlay_no_len(PG_FUNCTION_ARGS);
extern Datum name_text(PG_FUNCTION_ARGS);
extern Datum text_name(PG_FUNCTION_ARGS);
extern int varstr_cmp(char *arg1, int len1, char *arg2, int len2, Oid collid);
+extern int varstr_leven(const char *source, int slen, const char *target,
+ int tlen, int ins_c, int del_c, int sub_c);
+extern int varstr_leven_less_equal(const char *source, int slen,
+ const char *target, int tlen, int ins_c,
+ int del_c, int sub_c, int max_d);
extern List *textToQualifiedNameList(text *textval);
extern bool SplitIdentifierString(char *rawstring, char separator,
List **namelist);
--
1.9.1
--
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