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<hr><h1>scs2doubleCLEAN_BUT_SLOW.c</h1><div class="fragment"><pre>00001 <font class="comment">/** Conversion of SCS to floating-point double </font>
00002 <font class="comment">@file scs2double.c</font>
00003 <font class="comment"></font>
00004 <font class="comment">@author Defour David David.Defour@ens-lyon.fr</font>
00005 <font class="comment">@author Florent de Dinechin Florent.de.Dinechin@ens-lyon.fr </font>
00006 <font class="comment"></font>
00007 <font class="comment">This file is part of the SCS library.</font>
00008 <font class="comment">*/</font>
00009
00010 <font class="comment">/*</font>
00011 <font class="comment">Copyright (C) 2002 David Defour and Florent de Dinechin</font>
00012 <font class="comment"></font>
00013 <font class="comment"> This library is free software; you can redistribute it and/or</font>
00014 <font class="comment"> modify it under the terms of the GNU Lesser General Public</font>
00015 <font class="comment"> License as published by the Free Software Foundation; either</font>
00016 <font class="comment"> version 2.1 of the License, or (at your option) any later version.</font>
00017 <font class="comment"></font>
00018 <font class="comment"> This library is distributed in the hope that it will be useful,</font>
00019 <font class="comment"> but WITHOUT ANY WARRANTY; without even the implied warranty of</font>
00020 <font class="comment"> MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU</font>
00021 <font class="comment"> Lesser General Public License for more details.</font>
00022 <font class="comment"></font>
00023 <font class="comment"> You should have received a copy of the GNU Lesser General Public</font>
00024 <font class="comment"> License along with this library; if not, write to the Free Software</font>
00025 <font class="comment"> Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA</font>
00026 <font class="comment"></font>
00027 <font class="comment"> */</font>
00028 <font class="preprocessor">#include "<a class="code" href="scs_8h.html">scs.h</a>"</font>
00029 <font class="preprocessor">#include "<a class="code" href="scs__private_8h.html">scs_private.h</a>"</font>
00030
00031 <font class="comment"></font>
00032 <font class="comment">/** Convert a multiple precision number in scs format into a double</font>
00033 <font class="comment"> precision number.</font>
00034 <font class="comment"></font>
00035 <font class="comment">@warning "x" need to be normalized</font>
00036 <font class="comment"> */</font>
00037
00038
00039
00040
00041
00042
00043
00044
00045
00046
00047
00048
00049
00050 <font class="comment">/* computes the exponent from the index */</font>
00051 <font class="keyword">inline</font> <font class="keywordtype">void</font> computeExponent(<a class="code" href="structscs.html">scs_ptr</a> x, <font class="keywordtype">double</font> *res) {
00052 scs_db_number nb;
00053 <font class="keywordtype">int</font> i;
00054 <font class="keywordflow">if</font> ((X_IND < SCS_MAX_RANGE) && (X_IND > -SCS_MAX_RANGE)){
00055 <font class="comment">/* x is comfortably in the double-precision range */</font>
00056 <font class="comment">/* build the double 2^(X_IND*SCS_NB_BITS) */</font>
00057 nb.i[HI_ENDIAN] = ((X_IND)*SCS_NB_BITS +1023) << 20;
00058 nb.i[LO_ENDIAN] = 0;
00059 *res *= nb.d;
00060 }<font class="keywordflow">else</font> {
00061 <font class="comment">/* x may end up being a denormal or overflow */</font>
00062 i = X_IND;
00063 nb.d = 0;
00064 <font class="keywordflow">if</font> (X_IND > 0){
00065 <font class="comment">/* one of the following computations may lead to an overflow */</font>
00066 *res *=SCS_RADIX_RNG_DOUBLE; <font class="comment">/* 2^(SCS_NB_BITS.SCS_MAX_RANGE) */</font>
00067 i -= SCS_MAX_RANGE;
00068 <font class="keywordflow">while</font>((i-->0)&&(*res <= MAX_DOUBLE)) {
00069 <font class="comment">/* Thanks to the second test, this loop stops when an overflow is encountered */</font>
00070 *res *= SCS_RADIX_ONE_DOUBLE;
00071 }
00072 }<font class="keywordflow">else</font> {
00073 <font class="comment">/* One of the following computations may need to a denormal/underflow */</font>
00074 *res *=SCS_RADIX_MRNG_DOUBLE; <font class="comment">/* 2^-(SCS_NB_BITS.SCS_MAX_RANGE)*/</font>
00075 i += SCS_MAX_RANGE;
00076 <font class="keywordflow">while</font>((i++<0)&&(*res != 0)) {
00077 *res *=SCS_RADIX_MONE_DOUBLE;
00078 }
00079 }
00080 }
00081 <font class="comment">/* sign management */</font>
00082 <font class="keywordflow">if</font> (X_SGN < 0)
00083 *res = - *res;
00084 }
00085
00086
00087
00088 <font class="keywordtype">void</font> <a class="code" href="scs2double_8c.html#a0">scs_get_d</a>(<font class="keywordtype">double</font> *result, <a class="code" href="structscs.html">scs_ptr</a> x){
00089 scs_db_number nb, rndcorr;
00090 <font class="keywordtype">unsigned</font> <font class="keywordtype">long</font> <font class="keywordtype">long</font> <font class="keywordtype">int</font> lowpart, t1;
00091 <font class="keywordtype">int</font> exp;
00092
00093 <font class="comment">/* convert the MSB digit into a double, and store it in nb.d */</font>
00094 nb.d = (double)X_HW[0];
00095
00096 <font class="comment">/* place the two next digits in lowpart */</font>
00097 t1 = X_HW[1];
00098 lowpart = (t1 << SCS_NB_BITS) + X_HW[2];
00099
00100 <font class="comment">/* test for s/qNan, +/- Inf, +/- 0, placed here for obscure performance reasons */</font>
00101 <font class="keywordflow">if</font> (X_EXP != 1){*result = X_EXP; <font class="keywordflow">return</font>;}
00102
00103 <font class="comment">/* take the exponent of nb.d (will be in [0:SCS_NB_BITS])*/</font>
00104 exp = ((nb.i[HI_ENDIAN] & 0x7ff00000)>>20) - 1023;
00105 <font class="comment">/* align the rest of the mantissa to nb : shift by (2*SCS_NB_BITS)-53-exp */</font>
00106 lowpart = lowpart >> (exp+(2*SCS_NB_BITS)-53);
00107
00108 <font class="comment">/* Now look at the last bit to decide rounding */</font>
00109 <font class="keywordflow">if</font> (lowpart & 0x0000000000000001){
00110 <font class="comment">/* need to add an half-ulp */</font>
00111 rndcorr.i[LO_ENDIAN] = 0;
00112 rndcorr.i[HI_ENDIAN] = (exp+971) << 20; <font class="comment">/*((exp-52)+1023) << 20;*/</font>
00113 }<font class="keywordflow">else</font>{
00114 <font class="comment">/* need to add nothing*/</font>
00115 rndcorr.l = 0;
00116 }
00117
00118 lowpart = lowpart >> 1;
00119 nb.l = nb.l | lowpart; <font class="comment">/* Finish to fill the mantissa */</font>
00120 *result = nb.d + rndcorr.d; <font class="comment">/* rounded to nearest */</font>
00121
00122
00123 <font class="comment">/* now compute the exponent from the index */</font>
00124 computeExponent(x, result);
00125
00126 <font class="keywordflow">return</font>;
00127 }
00128
00129
00130
00131 <font class="keywordtype">void</font> scs_get_d_directed(<a class="code" href="structscs.html">scs_ptr</a> x, <font class="keywordtype">int</font> rndUp, <font class="keywordtype">double</font>* res)
00132 {
00133 <font class="keywordtype">unsigned</font> <font class="keywordtype">long</font> <font class="keywordtype">long</font> <font class="keywordtype">int</font> lowpart, t1;
00134 scs_db_number nb, rndcorr;
00135 <font class="keywordtype">int</font> i, exp, not_null;
00136
00137 nb.d = (double)X_HW[0];
00138
00139 t1 = X_HW[1];
00140 lowpart = (t1 << SCS_NB_BITS) + X_HW[2];
00141
00142 <font class="comment">/* s/qNan, +/- Inf, +/- 0 */</font>
00143 <font class="keywordflow">if</font> (X_EXP != 1){
00144 *res = X_EXP;
00145 <font class="keywordflow">return</font>;
00146 }
00147
00148 <font class="comment">/* take the exponent */</font>
00149 exp = ((nb.i[HI_ENDIAN] & 0x7ff00000)>>20) - 1023;
00150
00151 not_null = ((lowpart << (64+52 - 2*SCS_NB_BITS - exp))==0) ? 0 : 1;
00152
00153 <font class="comment">/* align the rest of the mantissa */</font>
00154 lowpart = lowpart >> (exp + 2*SCS_NB_BITS - 52);
00155
00156 <font class="comment">/* Finish to fill the mantissa */</font>
00157 nb.l = nb.l | lowpart;
00158
00159 <font class="comment">/* Test if we are not on an exact double precision number */</font>
00160 <font class="keywordflow">for</font> (i=3; i<SCS_NB_WORDS; i++)
00161 <font class="keywordflow">if</font> (X_HW[i]!=0) not_null = 1;
00162
00163 <font class="keywordflow">if</font> (rndUp && (not_null)){
00164 <font class="comment">/* we have to perform a rounded toward +inf (ulp >= 0.5) */</font>
00165 rndcorr.i[LO_ENDIAN] = 0;
00166 rndcorr.i[HI_ENDIAN] = (exp+971)<<20; <font class="comment">/*((exp-52)+1023) << 20;*/</font>
00167 } <font class="keywordflow">else</font> {
00168 rndcorr.d = 0.0;
00169 }
00170
00171 *res = nb.d + rndcorr.d; <font class="comment">/* make a rounded to nearest */</font>
00172 computeExponent(x, res);
00173 }
00174
00175
00176 <font class="comment">/*</font>
00177 <font class="comment"> * Rounded toward -Inf</font>
00178 <font class="comment"> */</font>
00179 <font class="keywordtype">void</font> scs_get_d_minf(<font class="keywordtype">double</font> *result, <a class="code" href="structscs.html">scs_ptr</a> x){
00180
00181 <font class="comment">/* round up the mantissa if negative */</font>
00182 scs_get_d_directed(x, (X_SGN<0), result);
00183
00184 <font class="keywordflow">return</font>;
00185 }
00186
00187
00188
00189 <font class="comment">/*</font>
00190 <font class="comment"> * Rounded toward +Inf</font>
00191 <font class="comment"> */</font>
00192 <font class="keywordtype">void</font> scs_get_d_pinf(<font class="keywordtype">double</font> *result, <a class="code" href="structscs.html">scs_ptr</a> x){
00193
00194 <font class="comment">/* round up the mantissa if positive */</font>
00195 scs_get_d_directed(x, (X_SGN>=0), result);
00196
00197 <font class="keywordflow">return</font>;
00198 }
00199
00200
00201
00202 <font class="comment">/*</font>
00203 <font class="comment"> * Rounded toward zero</font>
00204 <font class="comment"> */</font>
00205 <font class="keywordtype">void</font> scs_get_d_zero(<font class="keywordtype">double</font> *result, <a class="code" href="structscs.html">scs_ptr</a> x){
00206 <font class="comment">/* never round up the mantissa */</font>
00207 scs_get_d_directed(x, 0, result);
00208 }
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