Initial Contribution

libc/string/memmem.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+/*
+ * This uses the "Not So Naive" algorithm, a very simple but
+ * usually effective algorithm, see:
+ * http://www-igm.univ-mlv.fr/~lecroq/string/
+ */
+#include <string.h>
+
+void *memmem(const void *haystack, size_t n, const void *needle, size_t m)
+{
+    if (m > n || !m || !n)
+        return NULL;
+
+    if (__builtin_expect((m > 1), 1)) {
+        const unsigned char*  y = (const unsigned char*) haystack;
+        const unsigned char*  x = (const unsigned char*) needle;
+        size_t                j = 0;
+        size_t                k = 1, l = 2;
+
+        if (x[0] == x[1]) {
+            k = 2;
+            l = 1;
+        }
+        while (j <= n-m) {
+            if (x[1] != y[j+1]) {
+                j += k;
+            } else {
+                if (!memcmp(x+2, y+j+2, m-2) && x[0] == y[j])
+                    return (void*) &y[j];
+                j += l;
+            }
+        }
+    } else {
+        /* degenerate case */
+        return memchr(haystack, ((unsigned char*)needle)[0], n);
+    }
+    return NULL;
+}