| /* mpn_gcd_1 -- mpn and limb greatest common divisor. |
| |
| Copyright 1994, 1996, 2000, 2001 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" |
| |
| |
| /* Does not work for U == 0 or V == 0. It would be tough to make it work for |
| V == 0 since gcd(x,0) = x, and U does not generally fit in an mp_limb_t. |
| |
| The threshold for doing u%v when size==1 will vary by CPU according to |
| the speed of a division and the code generated for the main loop. Any |
| tuning for this is left to a CPU specific implementation. */ |
| |
| mp_limb_t |
| mpn_gcd_1 (mp_srcptr up, mp_size_t size, mp_limb_t vlimb) |
| { |
| mp_limb_t ulimb; |
| unsigned long zero_bits, u_low_zero_bits; |
| |
| ASSERT (size >= 1); |
| ASSERT (vlimb != 0); |
| ASSERT_MPN_NONZERO_P (up, size); |
| |
| ulimb = up[0]; |
| |
| /* Need vlimb odd for modexact, want it odd to get common zeros. */ |
| count_trailing_zeros (zero_bits, vlimb); |
| vlimb >>= zero_bits; |
| |
| if (size > 1) |
| { |
| /* Must get common zeros before the mod reduction. If ulimb==0 then |
| vlimb already gives the common zeros. */ |
| if (ulimb != 0) |
| { |
| count_trailing_zeros (u_low_zero_bits, ulimb); |
| zero_bits = MIN (zero_bits, u_low_zero_bits); |
| } |
| |
| ulimb = MPN_MOD_OR_MODEXACT_1_ODD (up, size, vlimb); |
| if (ulimb == 0) |
| goto done; |
| |
| goto strip_u_maybe; |
| } |
| |
| /* size==1, so up[0]!=0 */ |
| count_trailing_zeros (u_low_zero_bits, ulimb); |
| ulimb >>= u_low_zero_bits; |
| zero_bits = MIN (zero_bits, u_low_zero_bits); |
| |
| /* make u bigger */ |
| if (vlimb > ulimb) |
| MP_LIMB_T_SWAP (ulimb, vlimb); |
| |
| /* if u is much bigger than v, reduce using a division rather than |
| chipping away at it bit-by-bit */ |
| if ((ulimb >> 16) > vlimb) |
| { |
| ulimb %= vlimb; |
| if (ulimb == 0) |
| goto done; |
| goto strip_u_maybe; |
| } |
| |
| while (ulimb != vlimb) |
| { |
| ASSERT (ulimb & 1); |
| ASSERT (vlimb & 1); |
| |
| if (ulimb > vlimb) |
| { |
| ulimb -= vlimb; |
| do |
| { |
| ulimb >>= 1; |
| ASSERT (ulimb != 0); |
| strip_u_maybe: |
| ; |
| } |
| while ((ulimb & 1) == 0); |
| } |
| else /* vlimb > ulimb. */ |
| { |
| vlimb -= ulimb; |
| do |
| { |
| vlimb >>= 1; |
| ASSERT (vlimb != 0); |
| } |
| while ((vlimb & 1) == 0); |
| } |
| } |
| |
| done: |
| return vlimb << zero_bits; |
| } |