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authorMaciej W. Rozycki <macro@orcam.me.uk>2021-04-20 05:50:48 +0300
committerThomas Bogendoerfer <tsbogend@alpha.franken.de>2021-04-21 14:45:36 +0300
commitc1d337d45ec0a802299688e17d568c4e3a585895 (patch)
tree2bb74cb2980f11c7275479f4ca278ce0c3606cc3 /arch/mips/include/asm/div64.h
parentc49f71f60754acbff37505e1d16ca796bf8a8140 (diff)
downloadlinux-c1d337d45ec0a802299688e17d568c4e3a585895.tar.xz
MIPS: Avoid DIVU in `__div64_32' is result would be zero
We already check the high part of the divident against zero to avoid the costly DIVU instruction in that case, needed to reduce the high part of the divident, so we may well check against the divisor instead and set the high part of the quotient to zero right away. We need to treat the high part the divident in that case though as the remainder that would be calculated by the DIVU instruction we avoided. This has passed correctness verification with test_div64 and reduced the module's average execution time down to 1.0445s and 0.2619s from 1.0668s and 0.2629s respectively for an R3400 CPU @40MHz and a 5Kc CPU @160MHz. Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Diffstat (limited to 'arch/mips/include/asm/div64.h')
-rw-r--r--arch/mips/include/asm/div64.h6
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/mips/include/asm/div64.h b/arch/mips/include/asm/div64.h
index b252300e299d..a882a7bdf63e 100644
--- a/arch/mips/include/asm/div64.h
+++ b/arch/mips/include/asm/div64.h
@@ -68,9 +68,11 @@
\
__high = __div >> 32; \
__low = __div; \
- __upper = __high; \
\
- if (__high) { \
+ if (__high < __radix) { \
+ __upper = __high; \
+ __high = 0; \
+ } else { \
__asm__("divu $0, %z1, %z2" \
: "=x" (__modquot) \
: "Jr" (__high), "Jr" (__radix)); \