| /* mpn_mullow_n -- multiply two n-limb nunbers and return the low n limbs |
| of their products. |
| |
| THIS IS (FOR NOW) AN INTERNAL FUNCTION. IT IS ONLY SAFE TO REACH THIS |
| FUNCTION THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST GUARANTEED |
| THAT IT'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE. |
| |
| Copyright 2004, 2005 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" |
| |
| |
| #ifndef MULLOW_BASECASE_THRESHOLD |
| #define MULLOW_BASECASE_THRESHOLD 0 /* never use mpn_mul_basecase */ |
| #endif |
| |
| #ifndef MULLOW_DC_THRESHOLD |
| #define MULLOW_DC_THRESHOLD 3*MUL_KARATSUBA_THRESHOLD |
| #endif |
| |
| #ifndef MULLOW_MUL_N_THRESHOLD |
| #define MULLOW_MUL_N_THRESHOLD 10*MULLOW_DC_THRESHOLD |
| #endif |
| |
| /* Avoid zero allocations when MULLOW_BASECASE_THRESHOLD is 0. */ |
| #define MUL_BASECASE_ALLOC \ |
| (MULLOW_BASECASE_THRESHOLD_LIMIT == 0 ? 1 : 2*MULLOW_BASECASE_THRESHOLD_LIMIT) |
| |
| /* |
| FIXME: This function should accept a temporary area. |
| FIXME: Perhaps call mpn_kara_mul_n instead of mpn_mul_n? |
| THINK: If mpn_mul_basecase is always faster than mpn_mullow_basecase |
| (typically thanks to mpn_addmul_2) should we unconditionally use |
| mpn_mul_n? |
| FIXME: The recursive calls to mpn_mullow_n use sizes n/2 (one uses floor(n/2) |
| and the other ceil(n/2)). Depending on the values of the various |
| _THRESHOLDs, this may never trigger MULLOW_BASECASE_THRESHOLD. |
| Should we worry about this overhead? |
| */ |
| |
| void |
| mpn_mullow_n (mp_ptr rp, mp_srcptr xp, mp_srcptr yp, mp_size_t n) |
| { |
| if (BELOW_THRESHOLD (n, MULLOW_BASECASE_THRESHOLD)) |
| { |
| /* Allocate workspace of fixed size on stack: fast! */ |
| mp_limb_t ws[MUL_BASECASE_ALLOC]; |
| mpn_mul_basecase (ws, xp, n, yp, n); |
| MPN_COPY (rp, ws, n); |
| } |
| else if (BELOW_THRESHOLD (n, MULLOW_DC_THRESHOLD)) |
| { |
| mpn_mullow_basecase (rp, xp, yp, n); |
| } |
| else if (BELOW_THRESHOLD (n, MULLOW_MUL_N_THRESHOLD)) |
| { |
| /* Divide-and-conquer */ |
| mp_size_t n2 = n >> 1; /* floor(n/2) */ |
| mp_size_t n1 = n - n2; /* ceil(n/2) */ |
| mp_ptr tp; |
| TMP_SDECL; |
| TMP_SMARK; |
| tp = TMP_SALLOC_LIMBS (n1); |
| |
| /* Split as x = x1 2^(n1 GMP_NUMB_BITS) + x0, |
| y = y1 2^(n2 GMP_NUMB_BITS) + y0 */ |
| |
| /* x0 * y0 */ |
| mpn_mul_n (rp, xp, yp, n2); |
| if (n1 != n2) |
| rp[2 * n2] = mpn_addmul_1 (rp + n2, yp, n2, xp[n2]); |
| |
| /* x1 * y0 * 2^(n1 GMP_NUMB_BITS) */ |
| mpn_mullow_n (tp, xp + n1, yp, n2); |
| mpn_add_n (rp + n1, rp + n1, tp, n2); |
| |
| /* x0 * y1 * 2^(n2 GMP_NUMB_BITS) */ |
| mpn_mullow_n (tp, yp + n2, xp, n1); |
| mpn_add_n (rp + n2, rp + n2, tp, n1); |
| TMP_SFREE; |
| } |
| else |
| { |
| /* For really large operands, use plain mpn_mul_n but throw away upper n |
| limbs of result. */ |
| mp_ptr tp; |
| TMP_DECL; |
| TMP_MARK; |
| tp = TMP_ALLOC_LIMBS (2 * n); |
| |
| mpn_mul_n (tp, xp, yp, n); |
| MPN_COPY (rp, tp, n); |
| TMP_FREE; |
| } |
| } |