> Am 20.04.2021 um 04:50 schrieb Maciej W. Rozycki <macro@xxxxxxxxxxx>:
>
> We already check the high part of the divident against zero to avoid the
nit-picking: s/divident/dividend/
(seems to come from from Latin "dividendum" = the number that is to be divided).
> 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.
Impressive.
>
> Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
> ---
> I have made an experimental change on top of this to put `__div64_32' out
> of line, and that increases the averages respectively up to 1.0785s and
> 0.2705s. Not a terrible loss, especially compared to generic times quoted
> with 3/4, but still, so I think it would best be made where optimising for
> size, as noted in the cover letter.
> ---
> arch/mips/include/asm/div64.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> Index: linux-3maxp-div64/arch/mips/include/asm/div64.h
> ===================================================================
> --- linux-3maxp-div64.orig/arch/mips/include/asm/div64.h
> +++ linux-3maxp-div64/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)); \
