memmove.c

来自「newos is new operation system」· C语言 代码 · 共 72 行

/*
** Copyright 2001, Travis Geiselbrecht. All rights reserved.
** Distributed under the terms of the NewOS License.
*/
#include <string.h>
#include <sys/types.h>

#if !_ASM_MEMMOVE

typedef long word;

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

void *
memmove(void *dest, void const *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) {
		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++;
	} else {
		d += count;
		s += count;
		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;
			else
				len = ((long)d & lmask);

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

	return dest;
}

#endif