arch/h8300/include/asm/hash.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_HASH_H
   3 #define _ASM_HASH_H
   4
   5 /*
   6  * The later H8SX models have a 32x32-bit multiply, but the H8/300H
   7  * and H8S have only 16x16->32.  Since it's tolerably compact, this is
   8  * basically an inlined version of the __mulsi3 code.  Since the inputs
   9  * are not expected to be small, it's also simplfied by skipping the
  10  * early-out checks.
  11  *
  12  * (Since neither CPU has any multi-bit shift instructions, a
  13  * shift-and-add version is a non-starter.)
  14  *
  15  * TODO: come up with an arch-specific version of the hashing in fs/namei.c,
  16  * since that is heavily dependent on rotates.  Which, as mentioned, suck
  17  * horribly on H8.
  18  */
  19
  20 #if defined(CONFIG_CPU_H300H) || defined(CONFIG_CPU_H8S)
  21
  22 #define HAVE_ARCH__HASH_32 1
  23
  24 /*
  25  * Multiply by k = 0x61C88647.  Fitting this into three registers requires
  26  * one extra instruction, but reducing register pressure will probably
  27  * make that back and then some.
  28  *
  29  * GCC asm note: %e1 is the high half of operand %1, while %f1 is the
  30  * low half.  So if %1 is er4, then %e1 is e4 and %f1 is r4.
  31  *
  32  * This has been designed to modify x in place, since that's the most
  33  * common usage, but preserve k, since hash_64() makes two calls in
  34  * quick succession.
  35  */
  36 static inline u32 __attribute_const__ __hash_32(u32 x)
  37 {
  38         u32 temp;
  39
  40         asm(   "mov.w   %e1,%f0"
  41         "\n     mulxu.w %f2,%0"         /* klow * xhigh */
  42         "\n     mov.w   %f0,%e1"        /* The extra instruction */
  43         "\n     mov.w   %f1,%f0"
  44         "\n     mulxu.w %e2,%0"         /* khigh * xlow */
  45         "\n     add.w   %e1,%f0"
  46         "\n     mulxu.w %f2,%1"         /* klow * xlow */
  47         "\n     add.w   %f0,%e1"
  48         : "=&r" (temp), "=r" (x)
  49         : "%r" (GOLDEN_RATIO_32), "1" (x));
  50         return x;
  51 }
  52
  53 #endif
  54 #endif /* _ASM_HASH_H */