xref: /netbsd-src/external/lgpl3/mpc/dist/tests/double_rounding.c (revision 39f28e1e142c5bfb6be935a49cb55e2287fec7ea)
1 /*  double_rounding.c -- Functions for checking double rounding.
2 
3 Copyright (C) 2013, 2014 INRIA
4 
5 This file is part of GNU MPC.
6 
7 GNU MPC is free software; you can redistribute it and/or modify it under
8 the terms of the GNU Lesser General Public License as published by the
9 Free Software Foundation; either version 3 of the License, or (at your
10 option) any later version.
11 
12 GNU MPC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
14 FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
15 more details.
16 
17 You should have received a copy of the GNU Lesser General Public License
18 along with this program. If not, see http://www.gnu.org/licenses/ .
19 */
20 
21 #include "mpc-tests.h"
22 
23 /* return 1 if double rounding occurs;
24    return 0 otherwise */
25 static int
double_rounding_mpfr(mpfr_ptr lowprec,mpfr_ptr hiprec,int hiprec_inex,mpfr_rnd_t hiprec_rnd)26 double_rounding_mpfr (mpfr_ptr lowprec,
27                       mpfr_ptr hiprec, int hiprec_inex, mpfr_rnd_t hiprec_rnd)
28 {
29   mpfr_exp_t  hiprec_err;
30   mpfr_rnd_t  lowprec_rnd  = hiprec_rnd;
31   mpfr_prec_t lowprec_prec = mpfr_get_prec (lowprec);
32 
33   /* hiprec error is bounded by one ulp */
34   hiprec_err = mpfr_get_prec (hiprec) - 1;
35 
36   if (hiprec_rnd == MPFR_RNDN)
37     /* when rounding to nearest, use the trick for determining the
38        correct ternary value which is described in the MPFR
39        documentation */
40     {
41       hiprec_err++; /* error is bounded by one half-ulp */
42       lowprec_rnd = MPFR_RNDZ;
43       lowprec_prec++;
44     }
45 
46   return (hiprec_inex == 0
47           || mpfr_can_round (hiprec, hiprec_err, hiprec_rnd,
48                              lowprec_rnd, lowprec_prec));
49 }
50 
51 /* return 1 if double rounding occurs;
52    return 0 otherwise */
53 static int
double_rounding_mpc(mpc_ptr lowprec,mpc_ptr hiprec,int hiprec_inex,mpc_rnd_t hiprec_rnd)54 double_rounding_mpc (mpc_ptr lowprec,
55                      mpc_ptr hiprec, int hiprec_inex, mpc_rnd_t hiprec_rnd)
56 {
57   mpfr_ptr   lowprec_re = mpc_realref (lowprec);
58   mpfr_ptr   lowprec_im = mpc_imagref (lowprec);
59   mpfr_ptr   hiprec_re  = mpc_realref (hiprec);
60   mpfr_ptr   hiprec_im  = mpc_imagref (hiprec);
61   int        inex_re    = MPC_INEX_RE (hiprec_inex);
62   int        inex_im    = MPC_INEX_IM (hiprec_inex);
63   mpfr_rnd_t rnd_re     = MPC_RND_RE (hiprec_rnd);
64   mpfr_rnd_t rnd_im     = MPC_RND_IM (hiprec_rnd);
65 
66   return (double_rounding_mpfr (lowprec_re, hiprec_re, inex_re, rnd_re)
67           && double_rounding_mpfr (lowprec_im, hiprec_im, inex_im, rnd_im));
68 }
69 
70 /* check whether double rounding occurs; if not, round extra precise output
71    value and set reference parameter */
72 int
double_rounding(mpc_fun_param_t * params)73 double_rounding (mpc_fun_param_t *params)
74 {
75   int out;
76   const int offset = params->nbout + params->nbin;
77   int rnd_index = offset - params->nbrnd;
78 
79   for (out = 0; out < params->nbout; out++) {
80     if (params->T[out] == MPC)
81       {
82         int inex;
83 
84         MPC_ASSERT ((params->T[0] == MPC_INEX)
85                     || (params->T[0] == MPCC_INEX));
86         MPC_ASSERT ((params->T[offset] == MPC_INEX)
87                     || (params->T[offset] == MPCC_INEX));
88         MPC_ASSERT (params->T[out + offset] == MPC);
89         MPC_ASSERT (params->T[rnd_index] == MPC_RND);
90 
91         /*
92           For the time being, there may be either one or two rounding modes;
93           in the latter case, we assume that there are three outputs:
94           the inexact value and two complex numbers.
95         */
96         inex = (params->nbrnd == 1 ? params->P[0].mpc_inex
97                 : (out == 1 ? MPC_INEX1 (params->P[0].mpcc_inex)
98                    : MPC_INEX2 (params->P[0].mpcc_inex)));
99 
100         if (double_rounding_mpc (params->P[out + offset].mpc_data.mpc,
101                                  params->P[out].mpc,
102                                  inex,
103                                  params->P[rnd_index].mpc_rnd))
104           /* the high-precision value and the exact value round to the same
105              low-precision value */
106           {
107             int inex_hp, inex_re, inex_im;
108             inex = mpc_set (params->P[out + offset].mpc_data.mpc,
109                             params->P[out].mpc,
110                             params->P[rnd_index].mpc_rnd);
111             params->P[out + offset].mpc_data.known_sign_real = -1;
112             params->P[out + offset].mpc_data.known_sign_imag = -1;
113 
114             /* no double rounding means that the ternary value may come from
115                the high-precision calculation or from the rounding */
116             if (params->nbrnd == 1)
117               inex_hp = params->P[0].mpc_inex;
118             else /* nbrnd == 2 */
119               if (out == 1)
120                 inex_hp = MPC_INEX1 (params->P[0].mpcc_inex);
121               else /* out == 2 */
122                 inex_hp = MPC_INEX2 (params->P[0].mpcc_inex);
123 
124             if (MPC_INEX_RE (inex) == 0)
125               inex_re = MPC_INEX_RE (inex_hp);
126             else
127               inex_re = MPC_INEX_RE (inex);
128             if (MPC_INEX_IM (inex) == 0)
129               inex_im = MPC_INEX_IM (inex_hp);
130             else
131               inex_im = MPC_INEX_IM (inex);
132 
133             if (params->nbrnd == 1) {
134               params->P[offset].mpc_inex_data.real = inex_re;
135               params->P[offset].mpc_inex_data.imag = inex_im;
136             }
137             else /* nbrnd == 2 */
138               if (out == 1)
139                 params->P[offset].mpcc_inex = MPC_INEX (inex_re, inex_im);
140               else /* out == 2 */
141                 params->P[offset].mpcc_inex
142                   = MPC_INEX12 (params->P[offset].mpcc_inex,
143                                 MPC_INEX (inex_re, inex_im));
144 
145             rnd_index++;
146           }
147         else
148           /* double rounding occurs */
149           return 1;
150       }
151     else if (params->T[out] == MPFR)
152       {
153         MPC_ASSERT (params->T[0] == MPFR_INEX);
154         MPC_ASSERT (params->T[offset] == MPFR_INEX);
155         MPC_ASSERT (params->T[out + offset] == MPFR);
156         MPC_ASSERT (params->T[rnd_index] == MPFR_RND);
157 
158         if (double_rounding_mpfr (params->P[out + offset].mpfr_data.mpfr,
159                                   params->P[out].mpfr,
160                                   params->P[0].mpfr_inex,
161                                   params->P[rnd_index].mpfr_rnd))
162           /* the hight-precision value and the exact value round to the same
163              low-precision value */
164           {
165             int inex;
166             inex = mpfr_set (params->P[out + offset].mpfr_data.mpfr,
167                              params->P[out].mpfr,
168                              params->P[rnd_index].mpfr_rnd);
169             params->P[out + offset].mpfr_data.known_sign = -1;
170 
171             /* no double rounding means that the ternary value may comes from
172                the high-precision calculation or from the rounding */
173             if (inex == 0)
174               params->P[offset].mpfr_inex = params->P[0].mpfr_inex;
175             else
176               params->P[offset].mpfr_inex = inex;
177 
178             rnd_index++;
179           }
180         else
181           /* double rounding occurs */
182           return 1;
183       }
184   }
185   return 0;
186 }
187