Re: [PATCH v2] powerpc/math-emu: Update macros from gmp-6.1.2

On Tue, 20 Nov 2018 at 05:24, Nick Desaulniers [off-list ref] wrote:

quoted

The only functional change I noticed was this in udiv_qrnnd.

    __r1 = (n1) % __d1;
    __q1 = (n1) / __d1;

Becomes this:

    __q1 = (n1) / __d1;
    __r1 = (n1) - __q1 * __d1;

This is equivalent as it instead of calculating the remainder
using modulo, it uses the result of integer division to subtract the
count of 'whole' d1 from r1.

I don't understand this; why was this functional change made?

I couldn't see why. It pre-dates GMP's mecurial history that  .
                                              \

quoted

-    (q) = (UWtype) __q1 * __ll_B | __q0;                               \
+    (q) = __q1 * __ll_B | __q0;                                                \
     (r) = __r0;                                                                \
   } while (0)

This appears to now differ from the upstream source:
https://github.com/gcc-mirror/gcc/blob/f7289f563a5e447ac21a5901ed75aad0dbd37732/include/longlong.h#L1679

AIUI the upstream source is GMP:

 https://gmplib.org/repo/gmp/file/tip/longlong.h

If we're going to borrow implementations from GCC, let's borrow the
same implementation. Otherwise it's hard to have confidence in this
part of the patch.

I agree we should use the upstream source.

Segher, which tree contains the One True Upstream for longlong.h?

Cheers,

Joel