Ciao,
Il Lun, 27 Aprile 2015 4:45 pm, t...@gmplib.org ha scritto:
> @shell ~/gmp-repo$ tune/speed -s 1-1030 -f 2 -c mpn_neg mpn_com
> mpn_add_1_inplace.1
> overhead 6.78 cycles, precision 10000 units of 2.86e-10 secs, CPU freq
> 3500.08 MHz
> mpn_neg mpn_com mpn_add_1_inplace.1
> 1 #5.68 12.54 6.80
> 2 9.40 13.65 #8.19
> 4 16.25 11.40 #8.22
> 8 31.56 16.01 #6.84
> 1024 3689.67 1472.14 #8.29
> Perhaps mpn_neg should use a native mpn_com...
mpn_neg id defined in gmp.h, where we can not check for HAVE_NATIVE, but I
suspect that also the C version of mpn_com is faster than mpn_neg (in the
former, limbs do not depend on one another, no "carry" propagation).
Should we apply a patch like this?
diff -r 6e11cd70e19e gmp-h.in
--- a/gmp-h.in Mon Apr 27 22:46:53 2015 +0200
+++ b/gmp-h.in Tue Apr 28 22:41:52 2015 +0200
@@ -2191,13 +2191,10 @@
mp_limb_t
mpn_neg (mp_ptr __gmp_rp, mp_srcptr __gmp_up, mp_size_t __gmp_n)
{
- mp_limb_t __gmp_ul, __gmp_cy;
- __gmp_cy = 0;
- do {
- __gmp_ul = *__gmp_up++;
- *__gmp_rp++ = -__gmp_ul - __gmp_cy;
- __gmp_cy |= __gmp_ul != 0;
- } while (--__gmp_n != 0);
+ mp_limb_t __gmp_cy;
+ mpn_com (__gmp_rp, __gmp_up, __gmp_n);
+ __gmp_cy = 1;
+ __gmp_cy -= mpn_add_1 (__gmp_rp, __gmp_rp, __gmp_n, __gmp_cy);
return __gmp_cy;
}
#endif
It would slow down mpn_neg for small values of n...
Regards,
m
--
http://bodrato.it/
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