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authorGeorge Spelvin <linux@sciencehorizons.net>2016-06-07 19:45:06 -0400
committerHelge Deller <deller@gmx.de>2016-08-02 16:44:29 +0200
commit773e1c5fa4bf1faa25e119490b26ece2ef1bdb46 (patch)
treede6e0806522d4fe791a09a0e532b51f02288227d /arch/parisc/Kconfig
parent523d939ef98fd712632d93a5a2b588e477a7565e (diff)
download96b-common-773e1c5fa4bf1faa25e119490b26ece2ef1bdb46.tar.gz
parisc: Add <asm/hash.h>
PA-RISC is interesting; integer multiplies are implemented in the FPU, so are painful in the kernel. But it tries to be friendly to shift-and-add sequences for constant multiplies. __hash_32 is implemented using the same shift-and-add sequence as Microblaze, just scheduled for the PA7100. (It's 2-way superscalar but in-order, like the Pentium.) hash_64 was tricky, but a suggestion from Jason Thong allowed a good solution by breaking up the multiplier. After a lot of manual optimization, I found a 19-instruction sequence for the multiply that can be executed in 10 cycles using only 4 temporaries. (The PA8xxx can issue 4 instructions per cycle, but 2 must be ALU ops and 2 must be loads/stores. And the final add can't be paired.) An alternative considered, but ultimately not used, was Thomas Wang's 64-to-32-bit integer hash. At 12 instructions, it's smaller, but they're all sequentially dependent, so it has longer latency. https://web.archive.org/web/2011/http://www.concentric.net/~Ttwang/tech/inthash.htm http://burtleburtle.net/bob/hash/integer.html Signed-off-by: George Spelvin <linux@sciencehorizons.net> Cc: Helge Deller <deller@gmx.de> Cc: linux-parisc@vger.kernel.org Signed-off-by: Helge Deller <deller@gmx.de>
Diffstat (limited to 'arch/parisc/Kconfig')
-rw-r--r--arch/parisc/Kconfig1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index dc117385ce2e..cd8778103165 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -31,6 +31,7 @@ config PARISC
select TTY # Needed for pdc_cons.c
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_ARCH_AUDITSYSCALL
+ select HAVE_ARCH_HASH
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select HAVE_UNSTABLE_SCHED_CLOCK if (SMP || !64BIT)