/*
 * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <Kernel/Library/StdLib.h>

extern "C" {

void* memcpy(void* dest_ptr, void const* src_ptr, size_t n)
{
#if ARCH(X86_64)
    size_t dest = (size_t)dest_ptr;
    size_t src = (size_t)src_ptr;
    // FIXME: Support starting at an unaligned address.
    if (!(dest & 0x3) && !(src & 0x3) && n >= 12) {
        size_t size_ts = n / sizeof(size_t);
        asm volatile(
            "rep movsq\n"
            : "=S"(src), "=D"(dest)
            : "S"(src), "D"(dest), "c"(size_ts)
            : "memory");
        n -= size_ts * sizeof(size_t);
        if (n == 0)
            return dest_ptr;
    }
    asm volatile(
        "rep movsb\n" ::"S"(src), "D"(dest), "c"(n)
        : "memory");
#else
    u8* pd = (u8*)dest_ptr;
    u8 const* ps = (u8 const*)src_ptr;
    for (; n--;)
        *pd++ = *ps++;
#endif
    return dest_ptr;
}

void* memmove(void* dest, void const* src, size_t n)
{
    if (dest < src)
        return memcpy(dest, src, n);

    u8* pd = (u8*)dest;
    u8 const* ps = (u8 const*)src;
    for (pd += n, ps += n; n--;)
        *--pd = *--ps;
    return dest;
}

void* memset(void* dest_ptr, int c, size_t n)
{
#if ARCH(X86_64)
    size_t dest = (size_t)dest_ptr;
    // FIXME: Support starting at an unaligned address.
    if (!(dest & 0x3) && n >= 12) {
        size_t size_ts = n / sizeof(size_t);
        size_t expanded_c = explode_byte((u8)c);
        asm volatile(
            "rep stosq\n"
            : "=D"(dest)
            : "D"(dest), "c"(size_ts), "a"(expanded_c)
            : "memory");
        n -= size_ts * sizeof(size_t);
        if (n == 0)
            return dest_ptr;
    }
    asm volatile(
        "rep stosb\n"
        : "=D"(dest), "=c"(n)
        : "0"(dest), "1"(n), "a"(c)
        : "memory");
#else
    u8* pd = (u8*)dest_ptr;
    for (; n--;)
        *pd++ = c;
#endif
    return dest_ptr;
}

size_t strlen(char const* str)
{
    size_t len = 0;
    while (*(str++))
        ++len;
    return len;
}

size_t strnlen(char const* str, size_t maxlen)
{
    size_t len = 0;
    for (; len < maxlen && *str; str++)
        len++;
    return len;
}

int strcmp(char const* s1, char const* s2)
{
    for (; *s1 == *s2; ++s1, ++s2) {
        if (*s1 == 0)
            return 0;
    }
    return *(u8 const*)s1 < *(u8 const*)s2 ? -1 : 1;
}

int memcmp(void const* v1, void const* v2, size_t n)
{
    auto const* s1 = (u8 const*)v1;
    auto const* s2 = (u8 const*)v2;
    while (n-- > 0) {
        if (*s1++ != *s2++)
            return s1[-1] < s2[-1] ? -1 : 1;
    }
    return 0;
}

int strncmp(char const* s1, char const* s2, size_t n)
{
    if (!n)
        return 0;
    do {
        if (*s1 != *s2++)
            return *(unsigned char const*)s1 - *(unsigned char const*)--s2;
        if (*s1++ == 0)
            break;
    } while (--n);
    return 0;
}

char* strstr(char const* haystack, char const* needle)
{
    char nch;
    char hch;

    if ((nch = *needle++) != 0) {
        size_t len = strlen(needle);
        do {
            do {
                if ((hch = *haystack++) == 0)
                    return nullptr;
            } while (hch != nch);
        } while (strncmp(haystack, needle, len) != 0);
        --haystack;
    }
    return const_cast<char*>(haystack);
}
}