serenity/Kernel/Library/MiniStdLib.cpp

/*
 * Copyright (c) 2018-2020, Andreas Kling <[email protected]>
 *
 * 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);
        n -= size_ts * sizeof(size_t);
        asm volatile(
            "rep movsq\n"
            : "+S"(src), "+D"(dest), "+c"(size_ts)::"memory");
        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);
        n -= size_ts * sizeof(size_t);
        asm volatile(
            "rep stosq\n"
            : "+D"(dest), "+c"(size_ts)
            : "a"(expanded_c)
            : "memory");
        if (n == 0)
            return dest_ptr;
    }
    asm volatile(
        "rep stosb\n"
        : "+D"(dest), "+c"(n)
        : "a"(c)
        : "memory");
#else
    auto* dest = static_cast<u8*>(dest_ptr);

    auto is_word_aligned = [](auto ptr) {
        return reinterpret_cast<FlatPtr>(ptr) % sizeof(FlatPtr) == 0;
    };

    // Set bytes until destination is word-aligned.
    while (n > 0 && !is_word_aligned(dest)) {
        *dest++ = static_cast<u8>(c);
        n--;
    }

    // Set in word-sized chunks.
    FlatPtr exploded = explode_byte(c);

    auto* dest_word = reinterpret_cast<FlatPtr*>(dest);

#    pragma GCC unroll 8
    while (n >= sizeof(FlatPtr)) {
        *dest_word++ = exploded;
        n -= sizeof(FlatPtr);
    }
    dest = reinterpret_cast<u8*>(dest_word);

    // Set remaining tail bytes.
    while (n > 0) {
        *dest++ = static_cast<u8>(c);
        n--;
    }
#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);
}
}