Fix memmem behavior with empty needles.
Change-Id: I8b893d80c27b548652d843af9520d7adc8ba8902
diff --git a/libc/bionic/memmem.cpp b/libc/bionic/memmem.cpp
new file mode 100644
index 0000000..61d681f
--- /dev/null
+++ b/libc/bionic/memmem.cpp
@@ -0,0 +1,60 @@
+/*
+ * 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.
+ */
+
+#include <string.h>
+
+void* memmem(const void* void_haystack, size_t n, const void* void_needle, size_t m) {
+ const unsigned char* haystack = reinterpret_cast<const unsigned char*>(void_haystack);
+ const unsigned char* needle = reinterpret_cast<const unsigned char*>(void_needle);
+
+ if (n < m) return nullptr;
+
+ if (m == 0) return const_cast<void*>(void_haystack);
+ if (m == 1) return memchr(haystack, needle[0], n);
+
+ // This uses the "Not So Naive" algorithm, a very simple but usually effective algorithm.
+ // http://www-igm.univ-mlv.fr/~lecroq/string/
+ const unsigned char* y = haystack;
+ const unsigned char* x = 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 const_cast<unsigned char*>(&y[j]);
+ j += l;
+ }
+ }
+ return nullptr;
+}