kernel/lib/libc/string/memcpy.c

// Copyright 2016 The Fuchsia Authors
// Copyright (c) 2008 Travis Geiselbrecht
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#include <string.h>
#include <sys/types.h>


#if !_ASM_MEMCPY

typedef long word;

#define lsize sizeof(word)
#define lmask (lsize - 1)

// The attribute shouldn't be needed here, but without it LTO optimizes away
// this function which later causes a link failure.
// TODO(phosek): https://bugs.llvm.org/show_bug.cgi?id=34169
__USED void *memcpy(void *dest, const void *src, size_t count)
{
    char *d = (char *)dest;
    const char *s = (const char *)src;
    int len;

    if (count == 0 || dest == src)
        return dest;

    if (((long)d | (long)s) & lmask) {
        // src and/or dest do not align on word boundary
        if ((((long)d ^ (long)s) & lmask) || (count < lsize))
            len = count; // copy the rest of the buffer with the byte mover
        else
            len = lsize - ((long)d & lmask); // move the ptrs up to a word boundary

        count -= len;
        for (; len > 0; len--)
            *d++ = *s++;
    }
    for (len = count / lsize; len > 0; len--) {
        *(word *)d = *(word *)s;
        d += lsize;
        s += lsize;
    }
    for (len = count & lmask; len > 0; len--)
        *d++ = *s++;

    return dest;
}

#endif