include/asm-mn10300/unaligned.h

/* MN10300 Unaligned memory access handling
 *
 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#ifndef _ASM_UNALIGNED_H
#define _ASM_UNALIGNED_H

#include <asm/types.h>

#if 0
extern int __bug_unaligned_x(void *ptr);

/*
 * What is the most efficient way of loading/storing an unaligned value?
 *
 * That is the subject of this file.  Efficiency here is defined as
 * minimum code size with minimum register usage for the common cases.
 * It is currently not believed that long longs are common, so we
 * trade efficiency for the chars, shorts and longs against the long
 * longs.
 *
 * Current stats with gcc 2.7.2.2 for these functions:
 *
 *	ptrsize	get:	code	regs	put:	code	regs
 *	1		1	1		1	2
 *	2		3	2		3	2
 *	4		7	3		7	3
 *	8		20	6		16	6
 *
 * gcc 2.95.1 seems to code differently:
 *
 *	ptrsize	get:	code	regs	put:	code	regs
 *	1		1	1		1	2
 *	2		3	2		3	2
 *	4		7	4		7	4
 *	8		19	8		15	6
 *
 * which may or may not be more efficient (depending upon whether
 * you can afford the extra registers).  Hopefully the gcc 2.95
 * is inteligent enough to decide if it is better to use the
 * extra register, but evidence so far seems to suggest otherwise.
 *
 * Unfortunately, gcc is not able to optimise the high word
 * out of long long >> 32, or the low word from long long << 32
 */

#define __get_unaligned_2(__p)					\
	(__p[0] | __p[1] << 8)

#define __get_unaligned_4(__p)					\
	(__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24)

#define get_unaligned(ptr)					\
({								\
	unsigned int __v1, __v2;				\
	__typeof__(*(ptr)) __v;					\
	__u8 *__p = (__u8 *)(ptr);				\
								\
	switch (sizeof(*(ptr))) {				\
	case 1:	__v = *(ptr);			break;		\
	case 2: __v = __get_unaligned_2(__p);	break;		\
	case 4: __v = __get_unaligned_4(__p);	break;		\
	case 8:							\
		__v2 = __get_unaligned_4((__p+4));		\
		__v1 = __get_unaligned_4(__p);			\
		__v = ((unsigned long long)__v2 << 32 | __v1);	\
		break;						\
	default: __v = __bug_unaligned_x(__p);	break;		\
	}							\
	__v;							\
})


static inline void __put_unaligned_2(__u32 __v, register __u8 *__p)
{
	*__p++ = __v;
	*__p++ = __v >> 8;
}

static inline void __put_unaligned_4(__u32 __v, register __u8 *__p)
{
	__put_unaligned_2(__v >> 16, __p + 2);
	__put_unaligned_2(__v, __p);
}

static inline void __put_unaligned_8(const unsigned long long __v, __u8 *__p)
{
	/*
	 * tradeoff: 8 bytes of stack for all unaligned puts (2
	 * instructions), or an extra register in the long long
	 * case - go for the extra register.
	 */
	__put_unaligned_4(__v >> 32, __p + 4);
	__put_unaligned_4(__v, __p);
}

/*
 * Try to store an unaligned value as efficiently as possible.
 */
#define put_unaligned(val, ptr)						\
	({								\
		switch (sizeof(*(ptr))) {				\
		case 1:							\
			*(ptr) = (val);					\
			break;						\
		case 2:							\
			__put_unaligned_2((val), (__u8 *)(ptr));	\
			break;						\
		case 4:							\
			__put_unaligned_4((val), (__u8 *)(ptr));	\
			break;						\
		case 8:							\
			__put_unaligned_8((val), (__u8 *)(ptr));	\
			break;						\
		default:						\
			__bug_unaligned_x(ptr);				\
			break;						\
		}							\
		(void) 0;						\
	})


#else

#define get_unaligned(ptr) (*(ptr))
#define put_unaligned(val, ptr) ({ *(ptr) = (val); (void) 0; })

#endif

#endif