AK+LibC+Kernel: Move the implementation of memmem to AK

1 files changed, 87 insertions, 0 deletions

diff --git a/AK/MemMem.h b/AK/MemMem.h
new file mode 100644
index 0000000000..cc2edef4d3
--- /dev/null
+++ b/AK/MemMem.h
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. 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 HOLDER 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.
+ */
+
+#pragma once
+
+#include <AK/Assertions.h>
+#include <AK/Types.h>
+
+namespace AK {
+
+namespace {
+const static void* bitap_bitwise(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
+{
+    ASSERT(needle_length < 32);
+
+    u64 lookup = 0xfffffffe;
+
+    constexpr size_t mask_length = (size_t)((u8)-1) + 1;
+    u64 needle_mask[mask_length];
+
+    for (size_t i = 0; i < mask_length; ++i)
+        needle_mask[i] = 0xffffffff;
+
+    for (size_t i = 0; i < needle_length; ++i)
+        needle_mask[((const u8*)needle)[i]] &= ~(0x00000001 << i);
+
+    for (size_t i = 0; i < haystack_length; ++i) {
+        lookup |= needle_mask[((const u8*)haystack)[i]];
+        lookup <<= 1;
+
+        if (!(lookup & (0x00000001 << needle_length)))
+            return ((const u8*)haystack) + i - needle_length + 1;
+    }
+
+    return nullptr;
+}
+}
+
+static inline const void* memmem(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
+{
+    if (needle_length == 0)
+        return haystack;
+
+    if (haystack_length < needle_length)
+        return nullptr;
+
+    if (haystack_length == needle_length)
+        return __builtin_memcmp(haystack, needle, haystack_length) == 0 ? haystack : nullptr;
+
+    if (needle_length < 32)
+        return bitap_bitwise(haystack, haystack_length, needle, needle_length);
+
+    // Fallback to a slower search.
+    auto length_diff = haystack_length - needle_length;
+    for (size_t i = 0; i < length_diff; ++i) {
+        const auto* start = ((const u8*)haystack) + i;
+        if (__builtin_memcmp(start, needle, needle_length) == 0)
+            return start;
+    }
+
+    return nullptr;
+}
+
+}