| /* gcd_subdiv_step.c. |
| |
| THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY |
| SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST |
| GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE. |
| |
| Copyright 2003, 2004, 2005, 2008 Free Software Foundation, Inc. |
| |
| This file is part of the GNU MP Library. |
| |
| The GNU MP Library is free software; you can redistribute it and/or modify |
| it under the terms of the GNU Lesser General Public License as published by |
| the Free Software Foundation; either version 3 of the License, or (at your |
| option) any later version. |
| |
| The GNU MP Library is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
| or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public |
| License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public License |
| along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */ |
| |
| #include "gmp.h" |
| #include "gmp-impl.h" |
| #include "longlong.h" |
| |
| /* Used when mpn_hgcd or mpn_hgcd2 has failed. Then either one of a or |
| b is small, or the difference is small. Perform one subtraction |
| followed by one division. If the gcd is found, stores it in gp and |
| *gn, and returns zero. Otherwise, compute the reduced a and b, and |
| return the new size. */ |
| |
| /* FIXME: Check when the smaller number is a single limb, and invoke |
| * mpn_gcd_1. */ |
| mp_size_t |
| mpn_gcd_subdiv_step (mp_ptr gp, mp_size_t *gn, |
| mp_ptr ap, mp_ptr bp, mp_size_t n, mp_ptr tp) |
| { |
| mp_size_t an, bn; |
| |
| ASSERT (n > 0); |
| ASSERT (ap[n-1] > 0 || bp[n-1] > 0); |
| |
| an = bn = n; |
| MPN_NORMALIZE (ap, an); |
| MPN_NORMALIZE (bp, bn); |
| |
| if (UNLIKELY (an == 0)) |
| { |
| return_b: |
| MPN_COPY (gp, bp, bn); |
| *gn = bn; |
| return 0; |
| } |
| else if (UNLIKELY (bn == 0)) |
| { |
| return_a: |
| MPN_COPY (gp, ap, an); |
| *gn = an; |
| return 0; |
| } |
| |
| /* Arrange so that a > b, subtract an -= bn, and maintain |
| normalization. */ |
| if (an < bn) |
| MPN_PTR_SWAP (ap, an, bp, bn); |
| else if (an == bn) |
| { |
| int c; |
| MPN_CMP (c, ap, bp, an); |
| if (UNLIKELY (c == 0)) |
| goto return_a; |
| else if (c < 0) |
| MP_PTR_SWAP (ap, bp); |
| } |
| |
| ASSERT_NOCARRY (mpn_sub (ap, ap, an, bp, bn)); |
| MPN_NORMALIZE (ap, an); |
| ASSERT (an > 0); |
| |
| /* Arrange so that a > b, and divide a = q b + r */ |
| /* FIXME: an < bn happens when we have cancellation. If that is the |
| common case, then we could reverse the roles of a and b to avoid |
| the swap. */ |
| if (an < bn) |
| MPN_PTR_SWAP (ap, an, bp, bn); |
| else if (an == bn) |
| { |
| int c; |
| MPN_CMP (c, ap, bp, an); |
| if (UNLIKELY (c == 0)) |
| goto return_a; |
| else if (c < 0) |
| MP_PTR_SWAP (ap, bp); |
| } |
| |
| mpn_tdiv_qr (tp, ap, 0, ap, an, bp, bn); |
| |
| if (mpn_zero_p (ap, bn)) |
| goto return_b; |
| |
| return bn; |
| } |