Initial import

libc/alg/memmem.c

@@ -0,0 +1,97 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ This program is free software; you can redistribute it and/or modify         │
+│ it under the terms of the GNU General Public License as published by         │
+│ the Free Software Foundation; version 2 of the License.                      │
+│                                                                              │
+│ This program is distributed in the hope that it will be useful, but          │
+│ WITHOUT ANY WARRANTY; without even the implied warranty of                   │
+│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU             │
+│ General Public License for more details.                                     │
+│                                                                              │
+│ You should have received a copy of the GNU General Public License            │
+│ along with this program; if not, write to the Free Software                  │
+│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA                │
+│ 02110-1301 USA                                                               │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/alg/alg.h"
+#include "libc/macros.h"
+#include "libc/mem/mem.h"
+#include "libc/str/str.h"
+/* clang-format off */
+
+static void KnuthMorrisPrattInit(m, T, W)
+  ssize_t m, T[m + 1];
+  const char W[m];
+{
+  ssize_t i = 2;
+  ssize_t j = 0;
+  T[0] = -1;
+  T[1] = 0;
+  while (i < m) {
+    if (W[i - 1] == W[j]) {
+      T[i++] = j++ + 1;
+    } else if (j > 0) {
+      j = T[j];
+    } else {
+      T[i++] = 0;
+    }
+  }
+  T[m] = 0;
+}
+
+static size_t KnuthMorrisPratt(m, T, W, n, S)
+  const long n, m, T[m + 1];
+  const char W[m], S[n];
+{
+  long i = 0, j = 0;
+  while (i + j < n) {
+    if (W[i] == S[i + j]) {
+      i++;
+      if (i == m) break;
+    } else {
+      j = j + i - T[i];
+      if (i > 0) i = T[i];
+    }
+  }
+  return j;
+}
+
+/* clang-format on */
+
+/**
+ * Searches for fixed-length substring in memory region.
+ *
+ * @param haystack is the region of memory to be searched
+ * @param haystacklen is its character count
+ * @param needle contains the memory for which we're searching
+ * @param needlelen is its character count
+ * @return pointer to first result or NULL if not found
+ */
+void *(memmem)(const void *haystack_, size_t haystacklen, const void *needle_,
+               size_t needlelen) {
+  const char *haystack, *needle, *h;
+  haystack = haystack_;
+  needle = needle_;
+  if (needlelen > haystacklen) return NULL;
+  if (!needlelen) return (/*unconst*/ void *)haystack;
+  h = memchr(haystack, *needle, haystacklen);
+  if (!h || needlelen == 1) return (/*unconst*/ void *)h;
+  haystacklen -= h - haystack;
+  long stacktmp[16];
+  void *freeme = NULL;
+  long *T = (needlelen + 1 < ARRAYLEN(stacktmp))
+                ? &stacktmp[0]
+                : (freeme = malloc((needlelen + 1) * sizeof(long)));
+  KnuthMorrisPrattInit(needlelen, T, needle);
+  size_t i = KnuthMorrisPratt(needlelen, T, needle, haystacklen, h);
+  free(freeme);
+  if (i < haystacklen) {
+    return (/*unconst*/ char *)h + i * sizeof(char);
+  } else {
+    return NULL;
+  }
+}