libdecnumber/decimal128.c

   1 /* Decimal 128-bit format module from the decNumber C Library.
   2    Copyright (C) 2005 Free Software Foundation, Inc.
   3    Contributed by IBM Corporation.  Author Mike Cowlishaw.
   4
   5    This file is part of GCC.
   6
   7    GCC is free software; you can redistribute it and/or modify it under
   8    the terms of the GNU General Public License as published by the Free
   9    Software Foundation; either version 2, or (at your option) any later
  10    version.
  11
  12    In addition to the permissions in the GNU General Public License,
  13    the Free Software Foundation gives you unlimited permission to link
  14    the compiled version of this file into combinations with other
  15    programs, and to distribute those combinations without any
  16    restriction coming from the use of this file.  (The General Public
  17    License restrictions do apply in other respects; for example, they
  18    cover modification of the file, and distribution when not linked
  19    into a combine executable.)
  20
  21    GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  22    WARRANTY; without even the implied warranty of MERCHANTABILITY or
  23    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  24    for more details.
  25
  26    You should have received a copy of the GNU General Public License
  27    along with GCC; see the file COPYING.  If not, write to the Free
  28    Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  29    02110-1301, USA.  */
  30
  31 /* ------------------------------------------------------------------ */
  32 /* This module comprises the routines for decimal128 format numbers.  */
  33 /* Conversions are supplied to and from decNumber and String.         */
  34 /*                                                                    */
  35 /* No arithmetic routines are included; decNumber provides these.     */
  36 /*                                                                    */
  37 /* Error handling is the same as decNumber (qv.).                     */
  38 /* ------------------------------------------------------------------ */
  39 #include <string.h>             /* [for memset/memcpy] */
  40 #include <stdio.h>              /* [for printf] */
  41
  42 #define  DECNUMDIGITS 34        /* we need decNumbers with space for 34 */
  43 #include "config.h"
  44 #include "decNumber.h"          /* base number library */
  45 #include "decNumberLocal.h"     /* decNumber local types, etc. */
  46 #include "decimal128.h"         /* our primary include */
  47 #include "decUtility.h"         /* utility routines */
  48
  49 #if DECTRACE || DECCHECK
  50 void decimal128Show (const decimal128 *);       /* for debug */
  51 void decNumberShow (const decNumber *); /* .. */
  52 #endif
  53
  54 /* Useful macro */
  55 /* Clear a structure (e.g., a decNumber) */
  56 #define DEC_clear(d) memset(d, 0, sizeof(*d))
  57
  58 /* ------------------------------------------------------------------ */
  59 /* decimal128FromNumber -- convert decNumber to decimal128            */
  60 /*                                                                    */
  61 /*   ds is the target decimal128                                      */
  62 /*   dn is the source number (assumed valid)                          */
  63 /*   set is the context, used only for reporting errors               */
  64 /*                                                                    */
  65 /* The set argument is used only for status reporting and for the     */
  66 /* rounding mode (used if the coefficient is more than DECIMAL128_Pmax*/
  67 /* digits or an overflow is detected).  If the exponent is out of the */
  68 /* valid range then Overflow or Underflow will be raised.             */
  69 /* After Underflow a subnormal result is possible.                    */
  70 /*                                                                    */
  71 /* DEC_Clamped is set if the number has to be 'folded down' to fit,   */
  72 /* by reducing its exponent and multiplying the coefficient by a      */
  73 /* power of ten, or if the exponent on a zero had to be clamped.      */
  74 /* ------------------------------------------------------------------ */
  75 decimal128 *
  76 decimal128FromNumber (decimal128 * d128, const decNumber * dn, decContext * set)
  77 {
  78   uInt status = 0;              /* status accumulator */
  79   Int pad = 0;                  /* coefficient pad digits */
  80   decNumber dw;                 /* work */
  81   decContext dc;                /* .. */
  82   uByte isneg = dn->bits & DECNEG;      /* non-0 if original sign set */
  83   uInt comb, exp;               /* work */
  84
  85   /* If the number is finite, and has too many digits, or the exponent */
  86   /* could be out of range then we reduce the number under the */
  87   /* appropriate constraints */
  88   if (!(dn->bits & DECSPECIAL))
  89     {                           /* not a special value */
  90       Int ae = dn->exponent + dn->digits - 1;   /* adjusted exponent */
  91       if (dn->digits > DECIMAL128_Pmax  /* too many digits */
  92           || ae > DECIMAL128_Emax       /* likely overflow */
  93           || ae < DECIMAL128_Emin)
  94         {                       /* likely underflow */
  95           decContextDefault (&dc, DEC_INIT_DECIMAL128); /* [no traps] */
  96           dc.round = set->round;        /* use supplied rounding */
  97           decNumberPlus (&dw, dn, &dc); /* (round and check) */
  98           /* [this changes -0 to 0, but it will be restored below] */
  99           status |= dc.status;  /* save status */
 100           dn = &dw;             /* use the work number */
 101         }
 102       /* [this could have pushed number to Infinity or zero, so this */
 103       /* rounding must be done before we generate the decimal128] */
 104     }
 105
 106   DEC_clear (d128);             /* clean the target */
 107   if (dn->bits & DECSPECIAL)
 108     {                           /* a special value */
 109       uByte top;                /* work */
 110       if (dn->bits & DECINF)
 111         top = DECIMAL_Inf;
 112       else
 113         {                       /* sNaN or qNaN */
 114           if ((*dn->lsu != 0 || dn->digits > 1) /* non-zero coefficient */
 115               && (dn->digits < DECIMAL128_Pmax))
 116             {                   /* coefficient fits */
 117               decDensePackCoeff (dn, d128->bytes, sizeof (d128->bytes), 0);
 118             }
 119           if (dn->bits & DECNAN)
 120             top = DECIMAL_NaN;
 121           else
 122             top = DECIMAL_sNaN;
 123         }
 124       d128->bytes[0] = top;
 125     }
 126   else if (decNumberIsZero (dn))
 127     {                           /* a zero */
 128       /* set and clamp exponent */
 129       if (dn->exponent < -DECIMAL128_Bias)
 130         {
 131           exp = 0;
 132           status |= DEC_Clamped;
 133         }
 134       else
 135         {
 136           exp = dn->exponent + DECIMAL128_Bias; /* bias exponent */
 137           if (exp > DECIMAL128_Ehigh)
 138             {                   /* top clamp */
 139               exp = DECIMAL128_Ehigh;
 140               status |= DEC_Clamped;
 141             }
 142         }
 143       comb = (exp >> 9) & 0x18; /* combination field */
 144       d128->bytes[0] = (uByte) (comb << 2);
 145       exp &= 0xfff;             /* remaining exponent bits */
 146       decimal128SetExpCon (d128, exp);
 147     }
 148   else
 149     {                           /* non-zero finite number */
 150       uInt msd;                 /* work */
 151
 152       /* we have a dn that fits, but it may need to be padded */
 153       exp = (uInt) (dn->exponent + DECIMAL128_Bias);    /* bias exponent */
 154
 155       if (exp > DECIMAL128_Ehigh)
 156         {                       /* fold-down case */
 157           pad = exp - DECIMAL128_Ehigh;
 158           exp = DECIMAL128_Ehigh;       /* [to maximum] */
 159           status |= DEC_Clamped;
 160         }
 161
 162       decDensePackCoeff (dn, d128->bytes, sizeof (d128->bytes), pad);
 163
 164       /* save and clear the top digit */
 165       msd = ((unsigned) d128->bytes[1] << 2) & 0x0c;    /* top 2 bits */
 166       msd |= ((unsigned) d128->bytes[2] >> 6);  /* low 2 bits */
 167       d128->bytes[1] &= 0xfc;
 168       d128->bytes[2] &= 0x3f;
 169
 170       /* create the combination field */
 171       if (msd >= 8)
 172         comb = 0x18 | (msd & 0x01) | ((exp >> 11) & 0x06);
 173       else
 174         comb = (msd & 0x07) | ((exp >> 9) & 0x18);
 175       d128->bytes[0] = (uByte) (comb << 2);
 176       exp &= 0xfff;             /* remaining exponent bits */
 177       decimal128SetExpCon (d128, exp);
 178     }
 179
 180   if (isneg)
 181     decimal128SetSign (d128, 1);
 182   if (status != 0)
 183     decContextSetStatus (set, status);  /* pass on status */
 184
 185   /* decimal128Show(d128); */
 186   return d128;
 187 }
 188
 189 /* ------------------------------------------------------------------ */
 190 /* decimal128ToNumber -- convert decimal128 to decNumber              */
 191 /*   d128 is the source decimal128                                    */
 192 /*   dn is the target number, with appropriate space                  */
 193 /* No error is possible.                                              */
 194 /* ------------------------------------------------------------------ */
 195 decNumber *
 196 decimal128ToNumber (const decimal128 * d128, decNumber * dn)
 197 {
 198   uInt msd;                     /* coefficient MSD */
 199   decimal128 wk;                /* working copy, if needed */
 200   uInt top = d128->bytes[0] & 0x7f;     /* top byte, less sign bit */
 201   decNumberZero (dn);           /* clean target */
 202   /* set the sign if negative */
 203   if (decimal128Sign (d128))
 204     dn->bits = DECNEG;
 205
 206   if (top >= 0x78)
 207     {                           /* is a special */
 208       if ((top & 0x7c) == (DECIMAL_Inf & 0x7c))
 209         dn->bits |= DECINF;
 210       else if ((top & 0x7e) == (DECIMAL_NaN & 0x7e))
 211         dn->bits |= DECNAN;
 212       else
 213         dn->bits |= DECSNAN;
 214       msd = 0;                  /* no top digit */
 215     }
 216   else
 217     {                           /* have a finite number */
 218       uInt comb = top >> 2;     /* combination field */
 219       uInt exp;                 /* exponent */
 220
 221       if (comb >= 0x18)
 222         {
 223           msd = 8 + (comb & 0x01);
 224           exp = (comb & 0x06) << 11;    /* MSBs */
 225         }
 226       else
 227         {
 228           msd = comb & 0x07;
 229           exp = (comb & 0x18) << 9;
 230         }
 231       dn->exponent = exp + decimal128ExpCon (d128) - DECIMAL128_Bias;   /* remove bias */
 232     }
 233
 234   /* get the coefficient, unless infinite */
 235   if (!(dn->bits & DECINF))
 236     {
 237       Int bunches = DECIMAL128_Pmax / 3;        /* coefficient full bunches to convert */
 238       Int odd = 0;              /* assume MSD is 0 (no odd bunch) */
 239       if (msd != 0)
 240         {                       /* coefficient has leading non-0 digit */
 241           /* make a copy of the decimal128, with an extra bunch which has */
 242           /* the top digit ready for conversion */
 243           wk = *d128;           /* take a copy */
 244           wk.bytes[0] = 0;      /* clear all but coecon */
 245           wk.bytes[1] = 0;      /* .. */
 246           wk.bytes[2] &= 0x3f;  /* .. */
 247           wk.bytes[1] |= (msd >> 2);    /* and prefix MSD */
 248           wk.bytes[2] |= (msd << 6);    /* .. */
 249           odd++;                /* indicate the extra */
 250           d128 = &wk;           /* use the work copy */
 251         }
 252       decDenseUnpackCoeff (d128->bytes, sizeof (d128->bytes), dn, bunches,
 253                            odd);
 254     }
 255
 256   /* decNumberShow(dn); */
 257   return dn;
 258 }
 259
 260 /* ------------------------------------------------------------------ */
 261 /* to-scientific-string -- conversion to numeric string               */
 262 /* to-engineering-string -- conversion to numeric string              */
 263 /*                                                                    */
 264 /*   decimal128ToString(d128, string);                                */
 265 /*   decimal128ToEngString(d128, string);                             */
 266 /*                                                                    */
 267 /*  d128 is the decimal128 format number to convert                   */
 268 /*  string is the string where the result will be laid out            */
 269 /*                                                                    */
 270 /*  string must be at least 24 characters                             */
 271 /*                                                                    */
 272 /*  No error is possible, and no status can be set.                   */
 273 /* ------------------------------------------------------------------ */
 274 char *
 275 decimal128ToString (const decimal128 * d128, char *string)
 276 {
 277   decNumber dn;                 /* work */
 278   decimal128ToNumber (d128, &dn);
 279   decNumberToString (&dn, string);
 280   return string;
 281 }
 282
 283 char *
 284 decimal128ToEngString (const decimal128 * d128, char *string)
 285 {
 286   decNumber dn;                 /* work */
 287   decimal128ToNumber (d128, &dn);
 288   decNumberToEngString (&dn, string);
 289   return string;
 290 }
 291
 292 /* ------------------------------------------------------------------ */
 293 /* to-number -- conversion from numeric string                        */
 294 /*                                                                    */
 295 /*   decimal128FromString(result, string, set);                       */
 296 /*                                                                    */
 297 /*  result  is the decimal128 format number which gets the result of  */
 298 /*          the conversion                                            */
 299 /*  *string is the character string which should contain a valid      */
 300 /*          number (which may be a special value)                     */
 301 /*  set     is the context                                            */
 302 /*                                                                    */
 303 /* The context is supplied to this routine is used for error handling */
 304 /* (setting of status and traps) and for the rounding mode, only.     */
 305 /* If an error occurs, the result will be a valid decimal128 NaN.     */
 306 /* ------------------------------------------------------------------ */
 307 decimal128 *
 308 decimal128FromString (decimal128 * result, const char *string, decContext * set)
 309 {
 310   decContext dc;                /* work */
 311   decNumber dn;                 /* .. */
 312
 313   decContextDefault (&dc, DEC_INIT_DECIMAL128); /* no traps, please */
 314   dc.round = set->round;        /* use supplied rounding */
 315
 316   decNumberFromString (&dn, string, &dc);       /* will round if needed */
 317   decimal128FromNumber (result, &dn, &dc);
 318   if (dc.status != 0)
 319     {                           /* something happened */
 320       decContextSetStatus (set, dc.status);     /* .. pass it on */
 321     }
 322   return result;
 323 }
 324
 325
 326 #if DECTRACE || DECCHECK
 327 /* ------------------------------------------------------------------ */
 328 /* decimal128Show -- display a single in hexadecimal [debug aid]      */
 329 /*   d128 -- the number to show                                       */
 330 /* ------------------------------------------------------------------ */
 331 /* Also shows sign/cob/expconfields extracted */
 332 void
 333 decimal128Show (const decimal128 * d128)
 334 {
 335   char buf[DECIMAL128_Bytes * 2 + 1];
 336   Int i, j;
 337   j = 0;
 338   for (i = 0; i < DECIMAL128_Bytes; i++)
 339     {
 340       sprintf (&buf[j], "%02x", d128->bytes[i]);
 341       j = j + 2;
 342     }
 343   printf (" D128> %s [S:%d Cb:%02x E:%d]\n", buf,
 344           decimal128Sign (d128), decimal128Comb (d128),
 345           decimal128ExpCon (d128));
 346 }
 347 #endif