gem5 / arm / linux / b33c87328364e803d74e703d8e47821740dbfa87 / . / arch / m68k / include / asm / hash.h

#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 */ |