1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-05-28 08:35:09 +00:00

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.
This commit is contained in:
AnotherTest 2020-07-31 16:26:33 +04:30 committed by Andreas Kling
parent ad35436786
commit 1ad51325ad
5 changed files with 178 additions and 0 deletions

View file

@ -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;