/* 
** Copyright 2001, Travis Geiselbrecht. All rights reserved.
** Distributed under the terms of the NewOS License.
*/

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


/* From Bit twiddling hacks:
        http://graphics.stanford.edu/~seander/bithacks.html */
#define LACKS_ZERO_BYTE(value) \
        (((value - 0x01010101) & ~value & 0x80808080) == 0)


char*
strncpy(char* dest, const char* src, size_t count)
{
        char* tmp = dest;

        // Align destination buffer for four byte writes.
        while (((addr_t)dest & 3) != 0 && count != 0) {
                count--;
                if ((*dest++ = *src++) == '\0') {
                        memset(dest, '\0', count);
                        return tmp;
                }
        }

        if (count == 0)
                return tmp;

        if (((addr_t)src & 3) == 0) {
                // If the source and destination are aligned, copy a word
                // word at a time
                uint32* alignedSrc = (uint32*)src;
                uint32* alignedDest = (uint32*)dest;
                size_t alignedCount = count / 4;
                count -= alignedCount * 4;

                for (; alignedCount != 0 && LACKS_ZERO_BYTE(*alignedSrc);
                                alignedCount--)
                        *alignedDest++ = *alignedSrc++;

                count += alignedCount * 4;
                src = (char*)alignedSrc;
                dest = (char*)alignedDest;
        }

        // Deal with the remainder.
        while (count-- != 0) {
                if ((*dest++ = *src++) == '\0') {
                        memset(dest, '\0', count);
                        return tmp;
                }
        }

        return tmp;
}