t...@gmplib.org (Torbjörn Granlund) writes:
> ni...@lysator.liu.se (Niels Möller) writes:
>
> To not get multiple definitions in the case that there's some gcd_1.asm
> with an mpn_gcd_11 entry point, but no gcd_11.asm. If we don't organize
> asm code that way, the #if is useless and can be removed.
>
> I believe configure handles that too.
Nice, I wasn't aware of that.
BTW, below is one (untested) way to organize gcd_22. Wants an sub_mddmmss,
with output carry as a mask, analogous to the add_mssaaaa defined in
mod_1_1.c.
Regards,
/Niels
typedef struct {
mp_limb_t d[2];
} mp_double_limb_t;
mp_double_limb_t
gcd_22 (mp_limb_t u1, mp_limb_t u0, mp_limb_t v1, mp_limb_t v0)
{
mp_double_limb_t r;
ASSERT (u0 & v0 & 1);
while (u1 || v1) /* u1 == 0 can happen at most twice per call */
{
mp_limb_t vgtu, t1, t0;
sub_mddmmss (vgtu, t1, t0, u1, u0, v1, v0);
if (UNLIKELY (t0 == 0))
{
int c;
if (t1 == 0)
{
r.d[0] = u0;
r.d[1] = u1;
return r;
}
count_trailing_zeros (c, t1);
/* v1 = min (u1, v1) */
v1 += (vgtu & t1);
/* u0 = |u1 - v1| */
u0 = (t1 ^ vgtu) - vgtu;
u0 >>= c;
u1 = 0;
}
else
{
int c;
count_trailing_zeros (c, t0);
/* V <-- min (U, V).
Assembly version should use cmov. Another alternative,
avoiding carry propagation, would be
v0 += vgtu & t0; v1 += vtgu & (u1 - v1);
*/
add_ssaaaa (v1, v0, v1, v0, vgtu & t1, vgtu & t0);
/* U <-- |U - V|
No carry handling needed in this conditional negation,
since t0 != 0. */
u0 = (t0 ^ vtgu) - vgtu;
u1 = t1 ^ vgtu;
u0 = (u0 >> c) || (u1 << (GMP_LIMB_BITS - c));
u1 >>= c;
}
}
r.d[0] = mpn_gcd_11 (u0, v0);
r.d[1] = 0;
return r;
}
--
Niels Möller. PGP-encrypted email is preferred. Keyid 368C6677.
Internet email is subject to wholesale government surveillance.
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