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Diffstat (limited to 'sysdeps/generic/mul.c')
| -rw-r--r-- | sysdeps/generic/mul.c | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/sysdeps/generic/mul.c b/sysdeps/generic/mul.c new file mode 100644 index 0000000000..cd2acb5127 --- /dev/null +++ b/sysdeps/generic/mul.c @@ -0,0 +1,147 @@ +/* __mpn_mul -- Multiply two natural numbers. + +Copyright (C) 1991, 1993, 1994 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 Library General Public License as published by +the Free Software Foundation; either version 2 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 Library General Public +License for more details. + +You should have received a copy of the GNU Library General Public License +along with the GNU MP Library; see the file COPYING.LIB. If not, write to +the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" + +/* Multiply the natural numbers u (pointed to by UP, with USIZE limbs) + and v (pointed to by VP, with VSIZE limbs), and store the result at + PRODP. USIZE + VSIZE limbs are always stored, but if the input + operands are normalized. Return the most significant limb of the + result. + + NOTE: The space pointed to by PRODP is overwritten before finished + with U and V, so overlap is an error. + + Argument constraints: + 1. USIZE >= VSIZE. + 2. PRODP != UP and PRODP != VP, i.e. the destination + must be distinct from the multiplier and the multiplicand. */ + +/* If KARATSUBA_THRESHOLD is not already defined, define it to a + value which is good on most machines. */ +#ifndef KARATSUBA_THRESHOLD +#define KARATSUBA_THRESHOLD 32 +#endif + +mp_limb +#if __STDC__ +__mpn_mul (mp_ptr prodp, + mp_srcptr up, mp_size_t usize, + mp_srcptr vp, mp_size_t vsize) +#else +__mpn_mul (prodp, up, usize, vp, vsize) + mp_ptr prodp; + mp_srcptr up; + mp_size_t usize; + mp_srcptr vp; + mp_size_t vsize; +#endif +{ + mp_ptr prod_endp = prodp + usize + vsize - 1; + mp_limb cy; + mp_ptr tspace; + + if (vsize < KARATSUBA_THRESHOLD) + { + /* Handle simple cases with traditional multiplication. + + This is the most critical code of the entire function. All + multiplies rely on this, both small and huge. Small ones arrive + here immediately. Huge ones arrive here as this is the base case + for Karatsuba's recursive algorithm below. */ + mp_size_t i; + mp_limb cy_limb; + mp_limb v_limb; + + if (vsize == 0) + return 0; + + /* Multiply by the first limb in V separately, as the result can be + stored (not added) to PROD. We also avoid a loop for zeroing. */ + v_limb = vp[0]; + if (v_limb <= 1) + { + if (v_limb == 1) + MPN_COPY (prodp, up, usize); + else + MPN_ZERO (prodp, usize); + cy_limb = 0; + } + else + cy_limb = __mpn_mul_1 (prodp, up, usize, v_limb); + + prodp[usize] = cy_limb; + prodp++; + + /* For each iteration in the outer loop, multiply one limb from + U with one limb from V, and add it to PROD. */ + for (i = 1; i < vsize; i++) + { + v_limb = vp[i]; + if (v_limb <= 1) + { + cy_limb = 0; + if (v_limb == 1) + cy_limb = __mpn_add_n (prodp, prodp, up, usize); + } + else + cy_limb = __mpn_addmul_1 (prodp, up, usize, v_limb); + + prodp[usize] = cy_limb; + prodp++; + } + return cy_limb; + } + + tspace = (mp_ptr) alloca (2 * vsize * BYTES_PER_MP_LIMB); + MPN_MUL_N_RECURSE (prodp, up, vp, vsize, tspace); + + prodp += vsize; + up += vsize; + usize -= vsize; + if (usize >= vsize) + { + mp_ptr tp = (mp_ptr) alloca (2 * vsize * BYTES_PER_MP_LIMB); + do + { + MPN_MUL_N_RECURSE (tp, up, vp, vsize, tspace); + cy = __mpn_add_n (prodp, prodp, tp, vsize); + __mpn_add_1 (prodp + vsize, tp + vsize, vsize, cy); + prodp += vsize; + up += vsize; + usize -= vsize; + } + while (usize >= vsize); + } + + /* True: usize < vsize. */ + + /* Make life simple: Recurse. */ + + if (usize != 0) + { + __mpn_mul (tspace, vp, vsize, up, usize); + cy = __mpn_add_n (prodp, prodp, tspace, vsize); + __mpn_add_1 (prodp + vsize, tspace + vsize, usize, cy); + } + + return *prod_endp; +} |