From e1a7b0cc301feece6247b79e909a2683b64d07df Mon Sep 17 00:00:00 2001
From: Tal Einat <taleinat@gmail.com>
Date: Sun, 11 May 2014 02:37:32 +0300
Subject: [PATCH] added C implementation of subs-only hnm_byteslike

---
 fuzzysearch/_substitutions_only.c | 89 +++++++++++++++++++++++++++++++
 setup.py                          |  3 +-
 tests/test_substitutions_only.py  | 10 +++-
 3 files changed, 100 insertions(+), 2 deletions(-)

diff --git a/fuzzysearch/_substitutions_only.c b/fuzzysearch/_substitutions_only.c
index e108aa3..1f044b3 100644
--- a/fuzzysearch/_substitutions_only.c
+++ b/fuzzysearch/_substitutions_only.c
@@ -1,4 +1,5 @@
 #include <Python.h>
+#include "fuzzysearch/kmp.h"
 
 #if PY_MAJOR_VERSION >= 3
 #define IS_PY3K
@@ -75,11 +76,99 @@ substitutions_only_has_near_matches_byteslike(PyObject *self, PyObject *args)
     Py_RETURN_FALSE;
 }
 
+static PyObject *
+substitutions_only_has_near_matches_ngrams_byteslike(PyObject *self, PyObject *args)
+{
+    /* input params */
+    const char *subsequence;
+    const char *sequence;
+    int subseq_len, seq_len, max_substitutions;
+
+    int ngram_len, ngram_start, subseq_len_after_ngram;
+    const char *match_ptr, *seq_ptr, *subseq_ptr, *subseq_end;
+    int *kmpNext;
+    struct KMPstate kmp_state;
+    int n_differences, i;
+
+    if (!PyArg_ParseTuple(
+        args, "s#s#i",
+        &subsequence, &subseq_len,
+        &sequence, &seq_len,
+        &max_substitutions
+    )) {
+        return NULL;
+    }
+
+    if (seq_len < subseq_len) {
+        Py_RETURN_FALSE;
+    }
+
+    ngram_len = subseq_len / (max_substitutions + 1);
+    if (ngram_len == 0) {
+        PyErr_SetString(PyExc_ValueError,
+            "The subsequence's length must be greater than max_substitutions!"
+        );
+        return NULL;
+    }
+
+    subseq_end = subsequence + subseq_len;
+
+    kmpNext = (int *) malloc(ngram_len * sizeof(int));
+    if (kmpNext == NULL) {
+        return PyErr_NoMemory();
+    }
+
+    for (ngram_start = 0; ngram_start <= subseq_len - ngram_len; ngram_start += ngram_len) {
+        subseq_len_after_ngram = subseq_len - (ngram_start + ngram_len);
+
+        preKMP(subsequence + ngram_start, ngram_len, kmpNext);
+        kmp_state = KMP_init(subsequence + ngram_start,
+                             ngram_len,
+                             sequence + ngram_start,
+                             seq_len - ngram_start - subseq_len_after_ngram,
+                             kmpNext);
+
+        match_ptr = KMP_find_next(&kmp_state);
+        while (match_ptr != NULL) {
+            n_differences = max_substitutions + 1;
+
+            subseq_ptr = subsequence + ngram_start;
+            seq_ptr = match_ptr;
+            while (subseq_ptr != subsequence && n_differences) {
+                n_differences -= *(--subseq_ptr) != *(--seq_ptr);
+            }
+
+            if (n_differences) {
+                subseq_ptr = subseq_end - subseq_len_after_ngram;
+                seq_ptr = match_ptr + ngram_len;
+                while (subseq_ptr != subseq_end && n_differences) {
+                    n_differences -= (*subseq_ptr++) != (*seq_ptr++);
+                }
+
+                if (n_differences) {
+                    free(kmpNext);
+                    Py_RETURN_TRUE;
+                }
+            }
+
+            match_ptr = KMP_find_next(&kmp_state);
+        }
+    }
+
+    free(kmpNext);
+    Py_RETURN_FALSE;
+}
+
+
 static PyMethodDef substitutions_only_methods[] = {
     {"substitutions_only_has_near_matches_byteslike",
      substitutions_only_has_near_matches_byteslike,
      METH_VARARGS,
      "DOCSTRING."},
+    {"substitutions_only_has_near_matches_ngrams_byteslike",
+     substitutions_only_has_near_matches_ngrams_byteslike,
+     METH_VARARGS,
+     "DOCSTRING."},
     {NULL, NULL, 0, NULL}        /* Sentinel */
 };
 
diff --git a/setup.py b/setup.py
index bccba4c..d4ec900 100644
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,8 @@ history = open('HISTORY.rst').read().replace('.. :changelog:', '')
 
 _substitutions_only_module = Extension(
     'fuzzysearch._substitutions_only',
-    sources=['fuzzysearch/_substitutions_only.c'],
+    sources=['fuzzysearch/_substitutions_only.c', 'fuzzysearch/kmp.c'],
+    include_dirs=['.'],
 )
 _common_module = Extension(
     'fuzzysearch._common',
diff --git a/tests/test_substitutions_only.py b/tests/test_substitutions_only.py
index 0fda733..81f4aca 100644
--- a/tests/test_substitutions_only.py
+++ b/tests/test_substitutions_only.py
@@ -298,7 +298,9 @@ class TestHasNearMatchSubstitionsOnly(TestHasNearMatchSubstitionsOnlyBase,
 
 try:
     from fuzzysearch._substitutions_only import \
-        substitutions_only_has_near_matches_byteslike as hnm_subs_byteslike
+        substitutions_only_has_near_matches_byteslike as hnm_subs_byteslike, \
+        substitutions_only_has_near_matches_ngrams_byteslike as \
+            hnm_subs_ngrams_byteslike
 except ImportError:
     pass
 else:
@@ -309,3 +311,9 @@ else:
         def search(self, subsequence, sequence, max_subs):
             return hnm_subs_byteslike(subsequence, sequence, max_subs)
 
+    class TestHasNearMatchesSubstitionsNgramsByteslike(
+            TestHasNearMatchSubstitionsOnlyBase,
+            unittest.TestCase
+    ):
+        def search(self, subsequence, sequence, max_subs):
+            return hnm_subs_ngrams_byteslike(subsequence, sequence, max_subs)