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/*
* Copyright (c) 2020-2022, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/Array.h>
#include <AK/Assertions.h>
#include <AK/Span.h>
#include <AK/Types.h>
#include <AK/Vector.h>
namespace AK {
namespace Detail {
constexpr void const* bitap_bitwise(void const* haystack, size_t haystack_length, void const* needle, size_t needle_length)
{
VERIFY(needle_length < 32);
u32 lookup = 0xfffffffe;
constexpr size_t mask_length = (size_t)((u8)-1) + 1;
u32 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[((u8 const*)needle)[i]] &= ~(0x00000001 << i);
for (size_t i = 0; i < haystack_length; ++i) {
lookup |= needle_mask[((u8 const*)haystack)[i]];
lookup <<= 1;
if (0 == (lookup & (0x00000001 << needle_length)))
return ((u8 const*)haystack) + i - needle_length + 1;
}
return nullptr;
}
}
template<typename HaystackIterT>
inline Optional<size_t> memmem(HaystackIterT const& haystack_begin, HaystackIterT const& haystack_end, Span<const u8> needle) requires(requires { (*haystack_begin).data(); (*haystack_begin).size(); })
{
auto prepare_kmp_partial_table = [&] {
Vector<int, 64> table;
table.resize(needle.size());
size_t position = 1;
int candidate = 0;
table[0] = -1;
while (position < needle.size()) {
if (needle[position] == needle[candidate]) {
table[position] = table[candidate];
} else {
table[position] = candidate;
do {
candidate = table[candidate];
} while (candidate >= 0 && needle[candidate] != needle[position]);
}
++position;
++candidate;
}
return table;
};
auto table = prepare_kmp_partial_table();
size_t total_haystack_index = 0;
size_t current_haystack_index = 0;
int needle_index = 0;
auto haystack_it = haystack_begin;
while (haystack_it != haystack_end) {
auto&& chunk = *haystack_it;
if (current_haystack_index >= chunk.size()) {
current_haystack_index = 0;
++haystack_it;
continue;
}
if (needle[needle_index] == chunk[current_haystack_index]) {
++needle_index;
++current_haystack_index;
++total_haystack_index;
if ((size_t)needle_index == needle.size())
return total_haystack_index - needle_index;
continue;
}
needle_index = table[needle_index];
if (needle_index < 0) {
++needle_index;
++current_haystack_index;
++total_haystack_index;
}
}
return {};
}
inline Optional<size_t> memmem_optional(void const* haystack, size_t haystack_length, void const* needle, size_t needle_length)
{
if (needle_length == 0)
return 0;
if (haystack_length < needle_length)
return {};
if (haystack_length == needle_length) {
if (__builtin_memcmp(haystack, needle, haystack_length) == 0)
return 0;
return {};
}
if (needle_length < 32) {
auto const* ptr = Detail::bitap_bitwise(haystack, haystack_length, needle, needle_length);
if (ptr)
return static_cast<size_t>((FlatPtr)ptr - (FlatPtr)haystack);
return {};
}
// Fallback to KMP.
Array<Span<const u8>, 1> spans { Span<const u8> { (u8 const*)haystack, haystack_length } };
return memmem(spans.begin(), spans.end(), { (u8 const*)needle, needle_length });
}
inline void const* memmem(void const* haystack, size_t haystack_length, void const* needle, size_t needle_length)
{
auto offset = memmem_optional(haystack, haystack_length, needle, needle_length);
if (offset.has_value())
return ((u8 const*)haystack) + offset.value();
return nullptr;
}
}
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