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author | George Spelvin <linux@sciencehorizons.net> | 2016-05-25 14:19:49 -0400 |
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committer | George Spelvin <linux@sciencehorizons.net> | 2016-05-28 15:48:58 -0400 |
commit | 4684fe95300c071983f77653e354c040fe80a265 (patch) | |
tree | fec7e5e3b1034b346a723d5f09684b362d9261fc /arch/h8300/include | |
parent | 7b13277b682972c2ff8f6419e86c333d81936023 (diff) | |
download | linux-stable-4684fe95300c071983f77653e354c040fe80a265.tar.gz linux-stable-4684fe95300c071983f77653e354c040fe80a265.tar.bz2 linux-stable-4684fe95300c071983f77653e354c040fe80a265.zip |
h8300: Add <asm/hash.h>
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
Diffstat (limited to 'arch/h8300/include')
-rw-r--r-- | arch/h8300/include/asm/hash.h | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/arch/h8300/include/asm/hash.h b/arch/h8300/include/asm/hash.h new file mode 100644 index 000000000000..04cfbd2bd850 --- /dev/null +++ b/arch/h8300/include/asm/hash.h @@ -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 */ |