/* 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 modifyit under the terms of the GNU Lesser General Public License as published bythe Free Software Foundation; either version 2.1 of the License, or (at youroption) any later version. The GNU MP Library is distributed in the hope that it will be useful, butWITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITYor FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General PublicLicense for more details. You should have received a copy of the GNU Lesser General Public Licensealong with the GNU MP Library; see the file COPYING.LIB.  If not, write tothe 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)#elsempn_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;}