m68k: Add <asm/hash.h>

	select CPU_HAS_NO_MULDIV64

	select CPU_HAS_NO_UNALIGNED

	select GENERIC_CSUM

	select HAVE_ARCH_HASH

	help

	  The Freescale (was Motorola) 68000 CPU is the first generation of

	  the well known M68K family of processors. The CPU core as well as

#ifndef _ASM_HASH_H

#define _ASM_HASH_H

/*

 * If CONFIG_M68000=y (original mc68000/010), this file is #included

 * to work around the lack of a MULU.L instruction.

 */

#define HAVE_ARCH__HASH_32 1

/*

 * While it would be legal to substitute a different hash operation

 * entirely, let's keep it simple and just use an optimized multiply

 * by GOLDEN_RATIO_32 = 0x61C88647.

 *

 * The best way to do that appears to be to multiply by 0x8647 with

 * shifts and adds, and use mulu.w to multiply the high half by 0x61C8.

 *

 * Because the 68000 has multi-cycle shifts, this addition chain is

 * chosen to minimise the shift distances.

 *

 * Despite every attempt to spoon-feed it simple operations, GCC

 * 6.1.1 doggedly insists on doing annoying things like converting

 * "lsl.l #2,<reg>" (12 cycles) to two adds (8+8 cycles).

 *

 * It also likes to notice two shifts in a row, like "a = x << 2" and

 * "a <<= 7", and convert that to "a = x << 9".  But shifts longer

 * than 8 bits are extra-slow on m68k, so that's a lose.

 *

 * Since the 68000 is a very simple in-order processor with no

 * instruction scheduling effects on execution time, we can safely

 * take it out of GCC's hands and write one big asm() block.

 *

 * Without calling overhead, this operation is 30 bytes (14 instructions

 * plus one immediate constant) and 166 cycles.

 *

 * (Because %2 is fetched twice, it can't be postincrement, and thus it

 * can't be a fully general "g" or "m".  Register is preferred, but

 * offsettable memory or immediate will work.)

 */

static inline u32 __attribute_const__ __hash_32(u32 x)

{

	u32 a, b;

	asm(   "move.l %2,%0"	/* a = x * 0x0001 */

	"\n	lsl.l #2,%0"	/* a = x * 0x0004 */

	"\n	move.l %0,%1"

	"\n	lsl.l #7,%0"	/* a = x * 0x0200 */

	"\n	add.l %2,%0"	/* a = x * 0x0201 */

	"\n	add.l %0,%1"	/* b = x * 0x0205 */

	"\n	add.l %0,%0"	/* a = x * 0x0402 */

	"\n	add.l %0,%1"	/* b = x * 0x0607 */

	"\n	lsl.l #5,%0"	/* a = x * 0x8040 */

	: "=&d,d" (a), "=&r,r" (b)

	: "r,roi?" (x));	/* a+b = x*0x8647 */

	return ((u16)(x*0x61c8) << 16) + a + b;

}

#endif	/* _ASM_HASH_H */