memset.c

来自「newos is new operation system」· C语言 代码 · 共 38 行

/*
** Copyright 2005, Michael Noisternig. All rights reserved.
** Copyright 2001, Travis Geiselbrecht. All rights reserved.
** Distributed under the terms of the NewOS License.
*/
#include <string.h>
#include <sys/types.h>

void *
memset(void *s, int c, size_t count)
{
	char *xs = (char *) s;
	size_t len = (-(size_t)s) & (sizeof(size_t)-1);
	int cc = c & 0xff;

	if ( count > len ) {
		count -= len;
		cc |= cc << 8;
		cc |= cc << 16;

		// write to non-aligned memory byte-wise
		for ( ; len > 0; len-- )
			*xs++ = c;

		// write to aligned memory dword-wise
		for ( len = count/sizeof(size_t); len > 0; len-- )
			*((size_t *)xs)++ = cc;

		count &= sizeof(size_t)-1;
	}

	// write remaining bytes
	for ( ; count > 0; count-- )
		*xs++ = c;

	return s;
}