| /* SPDX-License-Identifier: GPL-2.0 */ |

| #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 */ |