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mpi-genesis~            1 /* mpihelp_udiv_w_sdiv -- implement udiv_qrnnd on machines with only signed
mpi-genesis~            2  *			  division.
mpi-genesis~            3  * Copyright (C) 1992, 1994, 1996, 1998 Free Software Foundation, Inc.
mpi-genesis~            4  * Contributed by Peter L. Montgomery.
mpi-genesis~            5  *
mpi-genesis~            6  * This file is part of GnuPG.
mpi-genesis~            7  *
mpi-genesis~            8  * GnuPG is free software; you can redistribute it and/or modify
mpi-genesis~            9  * it under the terms of the GNU General Public License as published by
mpi-genesis~           10  * the Free Software Foundation; either version 3 of the License, or
mpi-genesis~           11  * (at your option) any later version.
mpi-genesis~           12  *
mpi-genesis~           13  * GnuPG is distributed in the hope that it will be useful,
mpi-genesis~           14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
mpi-genesis~           15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
mpi-genesis~           16  * GNU General Public License for more details.
mpi-genesis~           17  *
mpi-genesis~           18  * You should have received a copy of the GNU General Public License
mpi-genesis~           19  * along with this program; if not, see <http://www.gnu.org/licenses/>.
mpi-genesis~           20  */
mpi-genesis~           21 
mpi-genesis~           22 #include <config.h>
mpi-genesis~           23 #include <stdio.h>
mpi-genesis~           24 #include <stdlib.h>
mpi-genesis~           25 #include "mpi-internal.h"
mpi-genesis~           26 #include "longlong.h"
mpi-genesis~           27 
mpi-genesis~           28 
mpi-genesis~           29 #if 0  /* not yet ported to MPI */
mpi-genesis~           30 
mpi-genesis~           31 mpi_limb_t
mpi-genesis~           32 mpihelp_udiv_w_sdiv( mpi_limp_t *rp,
mpi-genesis~           33 		     mpi_limp_t *a1,
mpi-genesis~           34 		     mpi_limp_t *a0,
mpi-genesis~           35 		     mpi_limp_t *d   )
mpi-genesis~           36 {
mpi-genesis~           37   mp_limb_t q, r;
mpi-genesis~           38   mp_limb_t c0, c1, b1;
mpi-genesis~           39 
mpi-genesis~           40   if ((mpi_limb_signed_t) d >= 0)
mpi-genesis~           41     {
mpi-genesis~           42       if (a1 < d - a1 - (a0 >> (BITS_PER_MP_LIMB - 1)))
mpi-genesis~           43 	{
mpi-genesis~           44 	  /* dividend, divisor, and quotient are nonnegative */
mpi-genesis~           45 	  sdiv_qrnnd (q, r, a1, a0, d);
mpi-genesis~           46 	}
mpi-genesis~           47       else
mpi-genesis~           48 	{
mpi-genesis~           49 	  /* Compute c1*2^32 + c0 = a1*2^32 + a0 - 2^31*d */
mpi-genesis~           50 	  sub_ddmmss (c1, c0, a1, a0, d >> 1, d << (BITS_PER_MP_LIMB - 1));
mpi-genesis~           51 	  /* Divide (c1*2^32 + c0) by d */
mpi-genesis~           52 	  sdiv_qrnnd (q, r, c1, c0, d);
mpi-genesis~           53 	  /* Add 2^31 to quotient */
mpi-genesis~           54 	  q += (mp_limb_t) 1 << (BITS_PER_MP_LIMB - 1);
mpi-genesis~           55 	}
mpi-genesis~           56     }
mpi-genesis~           57   else
mpi-genesis~           58     {
mpi-genesis~           59       b1 = d >> 1;			/* d/2, between 2^30 and 2^31 - 1 */
mpi-genesis~           60       c1 = a1 >> 1;			/* A/2 */
mpi-genesis~           61       c0 = (a1 << (BITS_PER_MP_LIMB - 1)) + (a0 >> 1);
mpi-genesis~           62 
mpi-genesis~           63       if (a1 < b1)			/* A < 2^32*b1, so A/2 < 2^31*b1 */
mpi-genesis~           64 	{
mpi-genesis~           65 	  sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */
mpi-genesis~           66 
mpi-genesis~           67 	  r = 2*r + (a0 & 1);		/* Remainder from A/(2*b1) */
mpi-genesis~           68 	  if ((d & 1) != 0)
mpi-genesis~           69 	    {
mpi-genesis~           70 	      if (r >= q)
mpi-genesis~           71 		r = r - q;
mpi-genesis~           72 	      else if (q - r <= d)
mpi-genesis~           73 		{
mpi-genesis~           74 		  r = r - q + d;
mpi-genesis~           75 		  q--;
mpi-genesis~           76 		}
mpi-genesis~           77 	      else
mpi-genesis~           78 		{
mpi-genesis~           79 		  r = r - q + 2*d;
mpi-genesis~           80 		  q -= 2;
mpi-genesis~           81 		}
mpi-genesis~           82 	    }
mpi-genesis~           83 	}
mpi-genesis~           84       else if (c1 < b1) 		/* So 2^31 <= (A/2)/b1 < 2^32 */
mpi-genesis~           85 	{
mpi-genesis~           86 	  c1 = (b1 - 1) - c1;
mpi-genesis~           87 	  c0 = ~c0;			/* logical NOT */
mpi-genesis~           88 
mpi-genesis~           89 	  sdiv_qrnnd (q, r, c1, c0, b1); /* (A/2) / (d/2) */
mpi-genesis~           90 
mpi-genesis~           91 	  q = ~q;			/* (A/2)/b1 */
mpi-genesis~           92 	  r = (b1 - 1) - r;
mpi-genesis~           93 
mpi-genesis~           94 	  r = 2*r + (a0 & 1);		/* A/(2*b1) */
mpi-genesis~           95 
mpi-genesis~           96 	  if ((d & 1) != 0)
mpi-genesis~           97 	    {
mpi-genesis~           98 	      if (r >= q)
mpi-genesis~           99 		r = r - q;
mpi-genesis~          100 	      else if (q - r <= d)
mpi-genesis~          101 		{
mpi-genesis~          102 		  r = r - q + d;
mpi-genesis~          103 		  q--;
mpi-genesis~          104 		}
mpi-genesis~          105 	      else
mpi-genesis~          106 		{
mpi-genesis~          107 		  r = r - q + 2*d;
mpi-genesis~          108 		  q -= 2;
mpi-genesis~          109 		}
mpi-genesis~          110 	    }
mpi-genesis~          111 	}
mpi-genesis~          112       else				/* Implies c1 = b1 */
mpi-genesis~          113 	{				/* Hence a1 = d - 1 = 2*b1 - 1 */
mpi-genesis~          114 	  if (a0 >= -d)
mpi-genesis~          115 	    {
mpi-genesis~          116 	      q = -1;
mpi-genesis~          117 	      r = a0 + d;
mpi-genesis~          118 	    }
mpi-genesis~          119 	  else
mpi-genesis~          120 	    {
mpi-genesis~          121 	      q = -2;
mpi-genesis~          122 	      r = a0 + 2*d;
mpi-genesis~          123 	    }
mpi-genesis~          124 	}
mpi-genesis~          125     }
mpi-genesis~          126 
mpi-genesis~          127   *rp = r;
mpi-genesis~          128   return q;
mpi-genesis~          129 }
mpi-genesis~          130 
mpi-genesis~          131 #endif
mpi-genesis~          132