atof-tahoe.c   [plain text]

/* atof_tahoe.c - turn a string into a Tahoe floating point number
   Copyright 1987, 1993, 2000 Free Software Foundation, Inc.

/* This is really a simplified version of atof_vax.c. I glommed it wholesale
   and then shaved it down. I don't even know how it works. (Don't you find
   my honesty refreshing?  Devon E Bowen <bowen@cs.buffalo.edu>

   I don't allow uppercase letters in the precision descriptors.
   i.e. 'f' and 'd' are allowed but 'F' and 'D' aren't.  */

#include "as.h"

/* Precision in LittleNums.  */
#define MAX_PRECISION (4)
#define D_PRECISION (4)
#define F_PRECISION (2)

/* Precision in chars.  */
#define D_PRECISION_CHARS (8)
#define F_PRECISION_CHARS (4)

/* Length in LittleNums of guard bits.  */
#define GUARD (2)

static const long int mask[] =
{
  0x00000000,
  0x00000001,
  0x00000003,
  0x00000007,
  0x0000000f,
  0x0000001f,
  0x0000003f,
  0x0000007f,
  0x000000ff,
  0x000001ff,
  0x000003ff,
  0x000007ff,
  0x00000fff,
  0x00001fff,
  0x00003fff,
  0x00007fff,
  0x0000ffff,
  0x0001ffff,
  0x0003ffff,
  0x0007ffff,
  0x000fffff,
  0x001fffff,
  0x003fffff,
  0x007fffff,
  0x00ffffff,
  0x01ffffff,
  0x03ffffff,
  0x07ffffff,
  0x0fffffff,
  0x1fffffff,
  0x3fffffff,
  0x7fffffff,
  0xffffffff
};

/* Shared between flonum_gen2tahoe and next_bits.  */
static int bits_left_in_littlenum;
static LITTLENUM_TYPE *littlenum_pointer;
static LITTLENUM_TYPE *littlenum_end;

#if __STDC__ == 1

int flonum_gen2tahoe (int format_letter, FLONUM_TYPE * f,
		      LITTLENUM_TYPE * words);

#else /* not __STDC__  */

int flonum_gen2tahoe ();

#endif /* not __STDC__  */

static int
next_bits (number_of_bits)
     int number_of_bits;
{
  int return_value;

  if (littlenum_pointer < littlenum_end)
    return 0;
  if (number_of_bits >= bits_left_in_littlenum)
    {
      return_value = mask[bits_left_in_littlenum] & *littlenum_pointer;
      number_of_bits -= bits_left_in_littlenum;
      return_value <<= number_of_bits;
      bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS - number_of_bits;
      littlenum_pointer--;
      if (littlenum_pointer >= littlenum_end)
	return_value |= ((*littlenum_pointer) >> (bits_left_in_littlenum)) &
	  mask[number_of_bits];
    }
  else
    {
      bits_left_in_littlenum -= number_of_bits;
      return_value = mask[number_of_bits] &
	((*littlenum_pointer) >> bits_left_in_littlenum);
    }
  return return_value;
}

static void
make_invalid_floating_point_number (words)
     LITTLENUM_TYPE *words;
{
  /* Floating Reserved Operand Code.  */
  *words = 0x8000;
}

static int			/* 0 means letter is OK.  */
what_kind_of_float (letter, precisionP, exponent_bitsP)
     /* In: lowercase please. What kind of float?  */
     char letter;

     /* Number of 16-bit words in the float.  */
     int *precisionP;

     /* Number of exponent bits.  */
     long int *exponent_bitsP;
{
  int retval;			/* 0: OK.  */

  retval = 0;
  switch (letter)
    {
    case 'f':
      *precisionP = F_PRECISION;
      *exponent_bitsP = 8;
      break;

    case 'd':
      *precisionP = D_PRECISION;
      *exponent_bitsP = 8;
      break;

    default:
      retval = 69;
      break;
    }
  return (retval);
}

/* Warning: This returns 16-bit LITTLENUMs, because that is what the
   VAX thinks in.  It is up to the caller to figure out any alignment
   problems and to conspire for the bytes/word to be emitted in the
   right order. Bigendians beware!  */

char *				/* Return pointer past text consumed.  */
atof_tahoe (str, what_kind, words)
     char *str;			/* Text to convert to binary.  */
     char what_kind;		/* 'd', 'f', 'g', 'h' */
     LITTLENUM_TYPE *words;	/* Build the binary here.  */
{
  FLONUM_TYPE f;
  LITTLENUM_TYPE bits[MAX_PRECISION + MAX_PRECISION + GUARD];
  /* Extra bits for zeroed low-order bits.  */
  /* The 1st MAX_PRECISION are zeroed, the last contain flonum bits.  */
  char *return_value;
  int precision;		/* Number of 16-bit words in the format.  */
  long int exponent_bits;

  return_value = str;
  f.low = bits + MAX_PRECISION;
  f.high = NULL;
  f.leader = NULL;
  f.exponent = NULL;
  f.sign = '\0';

  if (what_kind_of_float (what_kind, &precision, &exponent_bits))
    {
      /* We lost.  */
      return_value = NULL;
      make_invalid_floating_point_number (words);
    }
  if (return_value)
    {
      memset (bits, '\0', sizeof (LITTLENUM_TYPE) * MAX_PRECISION);

      /* Use more LittleNums than seems necessary:
	 the highest flonum may have 15 leading 0 bits, so could be
	 useless.  */
      f.high = f.low + precision - 1 + GUARD;

      if (atof_generic (&return_value, ".", "eE", &f))
	{
	  make_invalid_floating_point_number (words);
	  /* We lost.  */
	  return_value = NULL;
	}
      else
	{
	  if (flonum_gen2tahoe (what_kind, &f, words))
	    return_value = NULL;
	}
    }
  return return_value;
}

/* In: a flonum, a Tahoe floating point format.
   Out: a Tahoe floating-point bit pattern.  */

int				/* 0: OK.  */
flonum_gen2tahoe (format_letter, f, words)
     char format_letter;	/* One of 'd' 'f'.  */
     FLONUM_TYPE *f;
     LITTLENUM_TYPE *words;	/* Deliver answer here.  */
{
  LITTLENUM_TYPE *lp;
  int precision;
  long int exponent_bits;
  int return_value;		/* 0 == OK.  */

  return_value =
    what_kind_of_float (format_letter, &precision, &exponent_bits);
  if (return_value != 0)
    {
      make_invalid_floating_point_number (words);
    }
  else
    {
      if (f->low > f->leader)
	{
	  /* 0.0e0 seen.  */
	  memset (words, '\0', sizeof (LITTLENUM_TYPE) * precision);
	}
      else
	{
	  long int exponent_1;
	  long int exponent_2;
	  long int exponent_3;
	  long int exponent_4;
	  int exponent_skippage;
	  LITTLENUM_TYPE word1;

	  /* JF: Deal with new Nan, +Inf and -Inf codes.  */
	  if (f->sign != '-' && f->sign != '+')
	    {
	      make_invalid_floating_point_number (words);
	      return return_value;
	    }
	  /* All tahoe floating_point formats have:
	     Bit 15 is sign bit.
	     Bits 14:n are excess-whatever exponent.
	     Bits n-1:0 (if any) are most significant bits of fraction.
	     Bits 15:0 of the next word are the next most significant bits.
	     And so on for each other word.

	     So we need: number of bits of exponent, number of bits of
	     mantissa.  */

	  bits_left_in_littlenum = LITTLENUM_NUMBER_OF_BITS;
	  littlenum_pointer = f->leader;
	  littlenum_end = f->low;

	  /* Seek (and forget) 1st significant bit.  */
	  for (exponent_skippage = 0;
	       !next_bits (1);
	       exponent_skippage++)
	    ;

	  exponent_1 = f->exponent + f->leader + 1 - f->low;

	  /* Radix LITTLENUM_RADIX, point just higher than f -> leader.  */
	  exponent_2 = exponent_1 * LITTLENUM_NUMBER_OF_BITS;

	  /* Radix 2.  */
	  exponent_3 = exponent_2 - exponent_skippage;

	  /* Forget leading zeros, forget 1st bit.  */
	  exponent_4 = exponent_3 + (1 << (exponent_bits - 1));

	  /* Offset exponent.  */

	  if (exponent_4 & ~mask[exponent_bits])
	    {
	      /* Exponent overflow. Lose immediately.  */

	      make_invalid_floating_point_number (words);

	      /* We leave return_value alone: admit we read the
	        number, but return a floating exception because we
	        can't encode the number.  */
	    }
	  else
	    {
	      lp = words;

	      /* Word 1.  Sign, exponent and perhaps high bits.  */
	      /* Assume 2's complement integers.  */
	      word1 = ((exponent_4 & mask[exponent_bits])
		       << (15 - exponent_bits))
		| ((f->sign == '+') ? 0 : 0x8000)
		| next_bits (15 - exponent_bits);
	      *lp++ = word1;

	      /* The rest of the words are just mantissa bits.  */
	      for (; lp < words + precision; lp++)
		*lp = next_bits (LITTLENUM_NUMBER_OF_BITS);

	      if (next_bits (1))
		{
		  /* Since the NEXT bit is a 1, round UP the mantissa.
		     The cunning design of these hidden-1 floats permits
		     us to let the mantissa overflow into the exponent, and
		     it 'does the right thing'. However, we lose if the
		     highest-order bit of the lowest-order word flips.
		     Is that clear?  */

		  unsigned long int carry;

		  /* #if (sizeof(carry)) < ((sizeof(bits[0]) *
		     BITS_PER_CHAR) + 2) Please allow at least 1 more
		     bit in carry than is in a LITTLENUM.  We need
		     that extra bit to hold a carry during a LITTLENUM
		     carry propagation. Another extra bit (kept 0)
		     will assure us that we don't get a sticky sign
		     bit after shifting right, and that permits us to
		     propagate the carry without any masking of bits.
		     #endif  */
		  for (carry = 1, lp--;
		       carry && (lp >= words);
		       lp--)
		    {
		      carry = *lp + carry;
		      *lp = carry;
		      carry >>= LITTLENUM_NUMBER_OF_BITS;
		    }

		  if ((word1 ^ *words)
		      & (1 << (LITTLENUM_NUMBER_OF_BITS - 1)))
		    {
		      make_invalid_floating_point_number (words);
		      /* We leave return_value alone: admit we read
			 the number, but return a floating exception
			 because we can't encode the number.  */
		    }
		}		/* if (we needed to round up)  */
	    }			/* if (exponent overflow)  */
	}			/* if (0.0e0)  */
    }				/* if (float_type was OK)  */
  return return_value;
}

/* In:	input_line_pointer -> the 1st character of a floating-point
 *		number.
 *	1 letter denoting the type of statement that wants a
 *		binary floating point number returned.
 *	Address of where to build floating point literal.
 *		Assumed to be 'big enough'.
 *	Address of where to return size of literal (in chars).
 *
 * Out:	Input_line_pointer -> of next char after floating number.
 *	Error message, or 0.
 *	Floating point literal.
 *	Number of chars we used for the literal.  */

char *
md_atof (what_statement_type, literalP, sizeP)
     char what_statement_type;
     char *literalP;
     int *sizeP;
{
  LITTLENUM_TYPE words[MAX_PRECISION];
  register char kind_of_float;
  register int number_of_chars;
  register LITTLENUM_TYPE *littlenum_pointer;

  switch (what_statement_type)
    {
    case 'f':			/* .ffloat  */
    case 'd':			/* .dfloat  */
      kind_of_float = what_statement_type;
      break;

    default:
      kind_of_float = 0;
      break;
    }

  if (kind_of_float)
    {
      register LITTLENUM_TYPE *limit;

      input_line_pointer = atof_tahoe (input_line_pointer,
				       kind_of_float,
				       words);
      /* The atof_tahoe() builds up 16-bit numbers.
	 Since the assembler may not be running on
	 a different-endian machine, be very careful about
	 converting words to chars.  */
      number_of_chars = (kind_of_float == 'f' ? F_PRECISION_CHARS :
			 (kind_of_float == 'd' ? D_PRECISION_CHARS : 0));
      know (number_of_chars <= MAX_PRECISION * sizeof (LITTLENUM_TYPE));
      limit = words + (number_of_chars / sizeof (LITTLENUM_TYPE));
      for (littlenum_pointer = words;
	   littlenum_pointer < limit;
	   littlenum_pointer++)
	{
	  md_number_to_chars (literalP, *littlenum_pointer,
			      sizeof (LITTLENUM_TYPE));
	  literalP += sizeof (LITTLENUM_TYPE);
	}
    }
  else
    {
      number_of_chars = 0;
    }

  *sizeP = number_of_chars;
  return kind_of_float ? 0 : _("Bad call to md_atof()");
}