Marco Bodrato <bodr...@mail.dm.unipi.it> writes:
This is not really needed to solve a bug.
The comment before the mpn_mul_fft_decompose function says "We must
have nl <= 2*K*l", this means that we should never have ((dif = nl -
Kl) > Kl), and the code in that branch should never be used.
I noticed that at some point too, and have had a patch lying around for
quite a while:
*** /tmp/extdiff.kfdtyubq/gmp.1cbf890d4bff/mpn/generic/mul_fft.c Thu Mar 3 21:50:34 2022
--- /home/tege/prec/gmp/mpn/generic/mul_fft.c Tue Apr 6 10:57:52 2021
***************
*** 59,62 ****
--- 59,65 ----
*/
+ #include <stdio.h>
+
+
#ifdef TRACE
#undef TRACE
***************
*** 267,270 ****
--- 270,277 ----
cc = 0;
}
+ #if 0
+ /* FIXME: Remove rd assignments above. */
+ rd = ~r[m];
+ #endif
/* now complement {r, m}, subtract cc from r[0], subtract rd from r[m] */
***************
*** 682,726 ****
TMP_MARK;
if (nl > Kl) /* normalize {n, nl} mod 2^(Kl*GMP_NUMB_BITS)+1 */
{
mp_size_t dif = nl - Kl;
! mp_limb_signed_t cy;
tmp = TMP_BALLOC_LIMBS(Kl + 1);
! if (dif > Kl)
! {
! int subp = 0;
!
! cy = mpn_sub_n (tmp, n, n + Kl, Kl);
! n += 2 * Kl;
! dif -= Kl;
!
! /* now dif > 0 */
! while (dif > Kl)
! {
! if (subp)
! cy += mpn_sub_n (tmp, tmp, n, Kl);
! else
! cy -= mpn_add_n (tmp, tmp, n, Kl);
! subp ^= 1;
! n += Kl;
! dif -= Kl;
! }
! /* now dif <= Kl */
! if (subp)
! cy += mpn_sub (tmp, tmp, Kl, n, dif);
! else
! cy -= mpn_add (tmp, tmp, Kl, n, dif);
! if (cy >= 0)
! cy = mpn_add_1 (tmp, tmp, Kl, cy);
! else
! cy = mpn_sub_1 (tmp, tmp, Kl, -cy);
! }
! else /* dif <= Kl, i.e. nl <= 2 * Kl */
! {
! cy = mpn_sub (tmp, n, Kl, n + Kl, dif);
! cy = mpn_add_1 (tmp, tmp, Kl, cy);
! }
tmp[Kl] = cy;
nl = Kl + 1;
--- 689,703 ----
TMP_MARK;
+ ASSERT_ALWAYS (nl <= 2*Kl);
+
if (nl > Kl) /* normalize {n, nl} mod 2^(Kl*GMP_NUMB_BITS)+1 */
{
mp_size_t dif = nl - Kl;
! mp_limb_t cy;
tmp = TMP_BALLOC_LIMBS(Kl + 1);
! cy = mpn_sub (tmp, n, Kl, n + Kl, dif);
! cy = mpn_add_1 (tmp, tmp, Kl, cy);
tmp[Kl] = cy;
nl = Kl + 1;
(Not sure about the separate FIXME change therein; it looks strange to
me now.)
Feel free to clean this up.
--
Torbjörn
Please encrypt, key id 0xC8601622
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