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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libquadmath/] [printf/] [mul.c] - Rev 746
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/* mpn_mul -- Multiply two natural numbers. Copyright (C) 1991, 1993, 1994, 1996 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 2.1 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; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include <config.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_t #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_t 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_t cy_limb; mp_limb_t 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; }
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