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h8300: Add <asm/hash.h>

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This will improve the performance of hash_32() and hash_64(), but due
to complete lack of multi-bit shift instructions on H8, performance will
still be bad in surrounding code.

Designing H8-specific hash algorithms to work around that is a separate
project.  (But if the maintainers would like to get in touch...)

Signed-off-by: George Spelvin <linux@sciencehorizons.net>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: uclinux-h8-devel@lists.sourceforge.jp
This commit is contained in:
George Spelvin 2016-05-25 14:19:49 -04:00
parent 7b13277b68
commit 4684fe9530
2 changed files with 54 additions and 0 deletions
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1
arch/h8300/Kconfig
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@ -20,6 +20,7 @@ config H8300
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZO
select HAVE_ARCH_KGDB
select HAVE_ARCH_HASH
config RWSEM_GENERIC_SPINLOCK
def_bool y

53
arch/h8300/include/asm/hash.h Normal file
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@ -0,0 +1,53 @@
#ifndef _ASM_HASH_H
#define _ASM_HASH_H
/*
* The later H8SX models have a 32x32-bit multiply, but the H8/300H
* and H8S have only 16x16->32. Since it's tolerably compact, this is
* basically an inlined version of the __mulsi3 code. Since the inputs
* are not expected to be small, it's also simplfied by skipping the
* early-out checks.
*
* (Since neither CPU has any multi-bit shift instructions, a
* shift-and-add version is a non-starter.)
*
* TODO: come up with an arch-specific version of the hashing in fs/namei.c,
* since that is heavily dependent on rotates. Which, as mentioned, suck
* horribly on H8.
*/
#if defined(CONFIG_CPU_H300H) || defined(CONFIG_CPU_H8S)
#define HAVE_ARCH__HASH_32 1
/*
* Multiply by k = 0x61C88647. Fitting this into three registers requires
* one extra instruction, but reducing register pressure will probably
* make that back and then some.
*
* GCC asm note: %e1 is the high half of operand %1, while %f1 is the
* low half. So if %1 is er4, then %e1 is e4 and %f1 is r4.
*
* This has been designed to modify x in place, since that's the most
* common usage, but preserve k, since hash_64() makes two calls in
* quick succession.
*/
static inline u32 __attribute_const__ __hash_32(u32 x)
{
u32 temp;
asm( "mov.w %e1,%f0"
"\n mulxu.w %f2,%0" /* klow * xhigh */
"\n mov.w %f0,%e1" /* The extra instruction */
"\n mov.w %f1,%f0"
"\n mulxu.w %e2,%0" /* khigh * xlow */
"\n add.w %e1,%f0"
"\n mulxu.w %f2,%1" /* klow * xlow */
"\n add.w %f0,%e1"
: "=&r" (temp), "=r" (x)
: "%r" (GOLDEN_RATIO_32), "1" (x));
return x;
}
#endif
#endif /* _ASM_HASH_H */