Kernel+LibC: Implement 'memmem'

This commit adds an implementation of memmem, using the Bitap text
search algorithm for needles smaller than 32 bytes, and a naive loop
search for longer needles.

Kernel/StdLib.cpp

@@ -39,6 +39,34 @@ String copy_string_from_user(const char* user_str, size_t user_str_size)
     return String(user_str, length);
 }
 
+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;
+}
+}
+
 extern "C" {
 
 void copy_to_user(void* dest_ptr, const void* src_ptr, size_t n)
@@ -91,6 +119,31 @@ void* memmove(void* dest, const void* src, size_t n)
     return dest;
 }
 
+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 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 (memcmp(start, needle, needle_length) == 0)
+            return start;
+    }
+
+    return nullptr;
+}
+
 char* strcpy(char* dest, const char* src)
 {
     auto* dest_ptr = dest;

Kernel/StdLib.h

@@ -54,6 +54,7 @@ char* strdup(const char*);
 int memcmp(const void*, const void*, size_t);
 char* strrchr(const char* str, int ch);
 void* memmove(void* dest, const void* src, size_t n);
+const void* memmem(const void* haystack, size_t, const void* needle, size_t);
 
 inline u16 ntohs(u16 w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }
 inline u16 htons(u16 w) { return (w & 0xff) << 8 | ((w >> 8) & 0xff); }

Libraries/LibC/string.cpp

@@ -189,6 +189,59 @@ void* memmove(void* dest, const void* src, size_t n)
     return dest;
 }
 
+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;
+}
+}
+
+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 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 (memcmp(start, needle, needle_length) == 0)
+            return start;
+    }
+
+    return nullptr;
+}
+
 char* strcpy(char* dest, const char* src)
 {
     char* originalDest = dest;

Libraries/LibC/string.h

@@ -41,6 +41,7 @@ int memcmp(const void*, const void*, size_t);
 void* memcpy(void*, const void*, size_t);
 void* memmove(void*, const void*, size_t);
 void* memchr(const void*, int c, size_t);
+const void* memmem(const void* haystack, size_t, const void* needle, size_t);
 void bzero(void*, size_t);
 void bcopy(const void*, void*, size_t);
 void* memset(void*, int, size_t);

Tests/LibC/memmem-tests.cpp

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2020, Ali Mohammad Pur <ali.mpfard@gmail.com>
+ * 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.
+ */
+
+#include <AK/Types.h>
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+struct TestCase {
+    const u8* haystack;
+    size_t haystack_length;
+    const u8* needle;
+    size_t needle_length;
+    ssize_t matching_offset { -1 };
+};
+
+const static TestCase g_test_cases[] = {
+    { (const u8*) {}, 0u, (const u8*) {}, 0u, 0 },
+    { (const u8[]) { 1, 2, 3 }, 3u, (const u8[]) { 1, 2, 3 }, 3u, 0 },
+    { (const u8[]) { 1, 2, 4 }, 3u, (const u8[]) { 1, 2, 3 }, 3u, -1 },
+    { (const u8*)"abcdef", 6u, (const u8[]) {}, 0u, 0 },
+    { (const u8*)"abcdef", 6u, (const u8*)"de", 2u, 3 },
+    { (const u8[]) { 0, 1, 2, 5, 2, 5 }, 6u, (const u8[]) { 1 }, 1u, 1 },
+    { (const u8[]) { 0, 1, 2, 5, 2, 5 }, 6u, (const u8[]) { 1, 2 }, 2u, 1 },
+    { (const u8[]) { 0, 1, 1, 2 }, 4u, (const u8[]) { 1, 5 }, 2u, -1 },
+    { (const u8[64]) { 0 }, 64u, (const u8[33]) { 0 }, 33u, 0 },
+    { (const u8[64]) { 0, 1, 1, 2 }, 64u, (const u8[33]) { 1, 1 }, 2u, 1 },
+};
+
+int main()
+{
+    bool failed = false;
+    size_t i = 0;
+    for (const auto& test_case : g_test_cases) {
+        auto expected = test_case.matching_offset >= 0 ? test_case.haystack + test_case.matching_offset : nullptr;
+        auto result = memmem(test_case.haystack, test_case.haystack_length, test_case.needle, test_case.needle_length);
+        if (result != expected) {
+            failed = true;
+            fprintf(stderr, "Test %zu FAILED! expected %p, got %p\n", i, expected, result);
+        }
+        ++i;
+    }
+
+    return failed ? 1 : 0;
+}