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

diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index 986ea84..6c583db 100644 (file)
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -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

diff --git a/arch/h8300/include/asm/hash.h b/arch/h8300/include/asm/hash.h
new file mode 100644 (file)
index 0000000..04cfbd2
--- /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 */