gas/config/atof-tahoe.c

   1
   2 /* atof_tahoe.c - turn a string into a Tahoe floating point number
   3    Copyright (C) 1987 Free Software Foundation, Inc.
   4    */
   5
   6 /* This is really a simplified version of atof_vax.c. I glommed it wholesale
   7    and then shaved it down. I don't even know how it works. (Don't you find
   8    my honesty refreshing?  bowen@cs.Buffalo.EDU (Devon E Bowen)
   9
  10    I don't allow uppercase letters in the precision descrpitors. Ie 'f' and
  11    'd' are allowed but 'F' and 'D' aren't */
  12
  13 #include "as.h"
  14
  15 /* Precision in LittleNums. */
  16 #define MAX_PRECISION (4)
  17 #define D_PRECISION (4)
  18 #define F_PRECISION (2)
  19
  20 /* Precision in chars. */
  21 #define D_PRECISION_CHARS (8)
  22 #define F_PRECISION_CHARS (4)
  23
  24 /* Length in LittleNums of guard bits. */
  25 #define GUARD (2)
  26
  27 static const long int mask[] =
  28 {
  29   0x00000000,
  30   0x00000001,
  31   0x00000003,
  32   0x00000007,
  33   0x0000000f,
  34   0x0000001f,
  35   0x0000003f,
  36   0x0000007f,
  37   0x000000ff,
  38   0x000001ff,
  39   0x000003ff,
  40   0x000007ff,
  41   0x00000fff,
  42   0x00001fff,
  43   0x00003fff,
  44   0x00007fff,
  45   0x0000ffff,
  46   0x0001ffff,
  47   0x0003ffff,
  48   0x0007ffff,
  49   0x000fffff,
  50   0x001fffff,
  51   0x003fffff,
  52   0x007fffff,
  53   0x00ffffff,
  54   0x01ffffff,
  55   0x03ffffff,
  56   0x07ffffff,
  57   0x0fffffff,
  58   0x1fffffff,
  59   0x3fffffff,
  60   0x7fffffff,
  61   0xffffffff
  62 };
  63 \f
  64
  65 /* Shared between flonum_gen2tahoe and next_bits */
  66 static int bits_left_in_littlenum;
  67 static LITTLENUM_TYPE *littlenum_pointer;
  68 static LITTLENUM_TYPE *littlenum_end;
  69
  70 #if __STDC__ == 1
  71
  72 int flonum_gen2tahoe (int format_letter, FLONUM_TYPE * f, LITTLENUM_TYPE * words);
  73
  74 #else /* not __STDC__ */
  75
  76 int flonum_gen2tahoe ();
  77
  78 #endif /* not __STDC__ */
  79
  80
  81 static int
  82 next_bits (number_of_bits)
  83      int number_of_bits;
  84 {
  85   int return_value;
  86
  87   if (littlenum_pointer < littlenum_end)
  88     return 0;
  89   if (number_of_bits >= bits_left_in_littlenum)
  90     {
  91       return_value = mask[bits_left_in_littlenum] & *littlenum_pointer;
  92       number_of_bits -= bits_left_in_littlenum;
  93       return_value <<= number_of_bits;
  94       bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS - number_of_bits;
  95       littlenum_pointer--;
  96       if (littlenum_pointer >= littlenum_end)
  97         return_value |= ((*littlenum_pointer) >> (bits_left_in_littlenum)) &
  98           mask[number_of_bits];
  99     }
 100   else
 101     {
 102       bits_left_in_littlenum -= number_of_bits;
 103       return_value = mask[number_of_bits] &
 104         ((*littlenum_pointer) >> bits_left_in_littlenum);
 105     }
 106   return (return_value);
 107 }
 108
 109 static void
 110 make_invalid_floating_point_number (words)
 111      LITTLENUM_TYPE *words;
 112 {
 113   *words = 0x8000;              /* Floating Reserved Operand Code */
 114 }
 115 \f
 116 static int                      /* 0 means letter is OK. */
 117 what_kind_of_float (letter, precisionP, exponent_bitsP)
 118      char letter;               /* In: lowercase please. What kind of float? */
 119      int *precisionP;           /* Number of 16-bit words in the float. */
 120      long int *exponent_bitsP;  /* Number of exponent bits. */
 121 {
 122   int retval;                   /* 0: OK. */
 123
 124   retval = 0;
 125   switch (letter)
 126     {
 127     case 'f':
 128       *precisionP = F_PRECISION;
 129       *exponent_bitsP = 8;
 130       break;
 131
 132     case 'd':
 133       *precisionP = D_PRECISION;
 134       *exponent_bitsP = 8;
 135       break;
 136
 137     default:
 138       retval = 69;
 139       break;
 140     }
 141   return (retval);
 142 }
 143 \f
 144 /***********************************************************************\
 145 *                                                                       *
 146 *       Warning: this returns 16-bit LITTLENUMs, because that is        *
 147 *       what the VAX thinks in. It is up to the caller to figure        *
 148 *       out any alignment problems and to conspire for the bytes/word   *
 149 *       to be emitted in the right order. Bigendians beware!            *
 150 *                                                                       *
 151 \***********************************************************************/
 152
 153 char *                          /* Return pointer past text consumed. */
 154 atof_tahoe (str, what_kind, words)
 155      char *str;                 /* Text to convert to binary. */
 156      char what_kind;            /* 'd', 'f', 'g', 'h' */
 157      LITTLENUM_TYPE *words;     /* Build the binary here. */
 158 {
 159   FLONUM_TYPE f;
 160   LITTLENUM_TYPE bits[MAX_PRECISION + MAX_PRECISION + GUARD];
 161   /* Extra bits for zeroed low-order bits. */
 162   /* The 1st MAX_PRECISION are zeroed, */
 163   /* the last contain flonum bits. */
 164   char *return_value;
 165   int precision;                /* Number of 16-bit words in the format. */
 166   long int exponent_bits;
 167
 168   return_value = str;
 169   f.low = bits + MAX_PRECISION;
 170   f.high = NULL;
 171   f.leader = NULL;
 172   f.exponent = NULL;
 173   f.sign = '\0';
 174
 175   if (what_kind_of_float (what_kind, &precision, &exponent_bits))
 176     {
 177       return_value = NULL;      /* We lost. */
 178       make_invalid_floating_point_number (words);
 179     }
 180   if (return_value)
 181     {
 182       memset (bits, '\0', sizeof (LITTLENUM_TYPE) * MAX_PRECISION);
 183
 184       /* Use more LittleNums than seems */
 185       /* necessary: the highest flonum may have */
 186       /* 15 leading 0 bits, so could be useless. */
 187       f.high = f.low + precision - 1 + GUARD;
 188
 189       if (atof_generic (&return_value, ".", "eE", &f))
 190         {
 191           make_invalid_floating_point_number (words);
 192           return_value = NULL;  /* we lost */
 193         }
 194       else
 195         {
 196           if (flonum_gen2tahoe (what_kind, &f, words))
 197             {
 198               return_value = NULL;
 199             }
 200         }
 201     }
 202   return (return_value);
 203 }
 204 \f
 205 /*
 206  * In: a flonum, a Tahoe floating point format.
 207  * Out: a Tahoe floating-point bit pattern.
 208  */
 209
 210 int                             /* 0: OK. */
 211 flonum_gen2tahoe (format_letter, f, words)
 212      char format_letter;        /* One of 'd' 'f'. */
 213      FLONUM_TYPE *f;
 214      LITTLENUM_TYPE *words;     /* Deliver answer here. */
 215 {
 216   LITTLENUM_TYPE *lp;
 217   int precision;
 218   long int exponent_bits;
 219   int return_value;             /* 0 == OK. */
 220
 221   return_value = what_kind_of_float (format_letter, &precision, &exponent_bits);
 222   if (return_value != 0)
 223     {
 224       make_invalid_floating_point_number (words);
 225     }
 226   else
 227     {
 228       if (f->low > f->leader)
 229         {
 230           /* 0.0e0 seen. */
 231           memset (words, '\0', sizeof (LITTLENUM_TYPE) * precision);
 232         }
 233       else
 234         {
 235           long int exponent_1;
 236           long int exponent_2;
 237           long int exponent_3;
 238           long int exponent_4;
 239           int exponent_skippage;
 240           LITTLENUM_TYPE word1;
 241
 242           /* JF: Deal with new Nan, +Inf and -Inf codes */
 243           if (f->sign != '-' && f->sign != '+')
 244             {
 245               make_invalid_floating_point_number (words);
 246               return return_value;
 247             }
 248           /*
 249            * All tahoe floating_point formats have:
 250            * Bit 15 is sign bit.
 251            * Bits 14:n are excess-whatever exponent.
 252            * Bits n-1:0 (if any) are most significant bits of fraction.
 253            * Bits 15:0 of the next word are the next most significant bits.
 254            * And so on for each other word.
 255            *
 256            * So we need: number of bits of exponent, number of bits of
 257            * mantissa.
 258            */
 259
 260           bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS;
 261           littlenum_pointer = f->leader;
 262           littlenum_end = f->low;
 263           /* Seek (and forget) 1st significant bit */
 264           for (exponent_skippage = 0;
 265                !next_bits (1);
 266                exponent_skippage++)
 267             {
 268             }
 269           exponent_1 = f->exponent + f->leader + 1 - f->low;
 270           /* Radix LITTLENUM_RADIX, point just higher than f -> leader. */
 271           exponent_2 = exponent_1 * LITTLENUM_NUMBER_OF_BITS;
 272           /* Radix 2. */
 273           exponent_3 = exponent_2 - exponent_skippage;
 274           /* Forget leading zeros, forget 1st bit. */
 275           exponent_4 = exponent_3 + (1 << (exponent_bits - 1));
 276           /* Offset exponent. */
 277
 278           if (exponent_4 & ~mask[exponent_bits])
 279             {
 280               /*
 281                * Exponent overflow. Lose immediately.
 282                */
 283
 284               make_invalid_floating_point_number (words);
 285
 286               /*
 287                * We leave return_value alone: admit we read the
 288                * number, but return a floating exception
 289                * because we can't encode the number.
 290                */
 291             }
 292           else
 293             {
 294               lp = words;
 295
 296               /* Word 1. Sign, exponent and perhaps high bits. */
 297               /* Assume 2's complement integers. */
 298               word1 = ((exponent_4 & mask[exponent_bits]) << (15 - exponent_bits))
 299                 | ((f->sign == '+') ? 0 : 0x8000)
 300                 | next_bits (15 - exponent_bits);
 301               *lp++ = word1;
 302
 303               /* The rest of the words are just mantissa bits. */
 304               for (; lp < words + precision; lp++)
 305                 {
 306                   *lp = next_bits (LITTLENUM_NUMBER_OF_BITS);
 307                 }
 308
 309               if (next_bits (1))
 310                 {
 311                   /*
 312                    * Since the NEXT bit is a 1, round UP the mantissa.
 313                    * The cunning design of these hidden-1 floats permits
 314                    * us to let the mantissa overflow into the exponent, and
 315                    * it 'does the right thing'. However, we lose if the
 316                    * highest-order bit of the lowest-order word flips.
 317                    * Is that clear?
 318                    */
 319
 320                   unsigned long int carry;
 321
 322                   /*
 323                     #if (sizeof(carry)) < ((sizeof(bits[0]) * BITS_PER_CHAR) + 2)
 324                     Please allow at least 1 more bit in carry than is in a LITTLENUM.
 325                     We need that extra bit to hold a carry during a LITTLENUM carry
 326                     propagation. Another extra bit (kept 0) will assure us that we
 327                     don't get a sticky sign bit after shifting right, and that
 328                     permits us to propagate the carry without any masking of bits.
 329                     #endif
 330                     */
 331                   for (carry = 1, lp--;
 332                        carry && (lp >= words);
 333                        lp--)
 334                     {
 335                       carry = *lp + carry;
 336                       *lp = carry;
 337                       carry >>= LITTLENUM_NUMBER_OF_BITS;
 338                     }
 339
 340                   if ((word1 ^ *words) & (1 << (LITTLENUM_NUMBER_OF_BITS - 1)))
 341                     {
 342                       make_invalid_floating_point_number (words);
 343                       /*
 344                        * We leave return_value alone: admit we read the
 345                        * number, but return a floating exception
 346                        * because we can't encode the number.
 347                        */
 348                     }
 349                 }               /* if (we needed to round up) */
 350             }                   /* if (exponent overflow) */
 351         }                       /* if (0.0e0) */
 352     }                           /* if (float_type was OK) */
 353   return (return_value);
 354 }
 355 \f
 356 /*
 357  *              md_atof()
 358  *
 359  * In:  input_line_pointer -> the 1st character of a floating-point
 360  *              number.
 361  *      1 letter denoting the type of statement that wants a
 362  *              binary floating point number returned.
 363  *      Address of where to build floating point literal.
 364  *              Assumed to be 'big enough'.
 365  *      Address of where to return size of literal (in chars).
 366  *
 367  * Out: Input_line_pointer -> of next char after floating number.
 368  *      Error message, or 0.
 369  *      Floating point literal.
 370  *      Number of chars we used for the literal.
 371  */
 372
 373 char *
 374 md_atof (what_statement_type, literalP, sizeP)
 375      char what_statement_type;
 376      char *literalP;
 377      int *sizeP;
 378 {
 379   LITTLENUM_TYPE words[MAX_PRECISION];
 380   register char kind_of_float;
 381   register int number_of_chars;
 382   register LITTLENUM_TYPE *littlenum_pointer;
 383
 384   switch (what_statement_type)
 385     {
 386     case 'f':                   /* .ffloat */
 387     case 'd':                   /* .dfloat */
 388       kind_of_float = what_statement_type;
 389       break;
 390
 391     default:
 392       kind_of_float = 0;
 393       break;
 394     };
 395
 396   if (kind_of_float)
 397     {
 398       register LITTLENUM_TYPE *limit;
 399
 400       input_line_pointer = atof_tahoe (input_line_pointer,
 401                                        kind_of_float,
 402                                        words);
 403       /*
 404        * The atof_tahoe() builds up 16-bit numbers.
 405        * Since the assembler may not be running on
 406        * a different-endian machine, be very careful about
 407        * converting words to chars.
 408        */
 409       number_of_chars = (kind_of_float == 'f' ? F_PRECISION_CHARS :
 410                          (kind_of_float == 'd' ? D_PRECISION_CHARS : 0));
 411       know (number_of_chars <= MAX_PRECISION * sizeof (LITTLENUM_TYPE));
 412       limit = words + (number_of_chars / sizeof (LITTLENUM_TYPE));
 413       for (littlenum_pointer = words;
 414            littlenum_pointer < limit;
 415            littlenum_pointer++)
 416         {
 417           md_number_to_chars (literalP, *littlenum_pointer,
 418                               sizeof (LITTLENUM_TYPE));
 419           literalP += sizeof (LITTLENUM_TYPE);
 420         };
 421     }
 422   else
 423     {
 424       number_of_chars = 0;
 425     };
 426
 427   *sizeP = number_of_chars;
 428   return kind_of_float ? 0 : "Bad call to md_atof()";
 429 }
 430
 431 /* atof_tahoe.c */