atof-generic.c

来自「基于4个mips核的noc设计」· C语言 代码 · 共 635 行 · 第 1/2 页

      unsigned int more_than_enough_bits_for_digits;
      unsigned int more_than_enough_littlenums_for_digits;
      unsigned int size_of_digits_in_littlenums;
      unsigned int size_of_digits_in_chars;
      FLONUM_TYPE power_of_10_flonum;
      FLONUM_TYPE digits_flonum;

      precision = (address_of_generic_floating_point_number->high
		   - address_of_generic_floating_point_number->low
		   + 1);	/* Number of destination littlenums.  */

      /* Includes guard bits (two littlenums worth) */
#if 0 /* The integer version below is very close, and it doesn't
	 require floating point support (which is currently buggy on
	 the Alpha).  */
      maximum_useful_digits = (((double) (precision - 2))
			       * ((double) (LITTLENUM_NUMBER_OF_BITS))
			       / (LOG_TO_BASE_2_OF_10))
	+ 2;			/* 2 :: guard digits.  */
#else
      maximum_useful_digits = (((precision - 2))
			       * ( (LITTLENUM_NUMBER_OF_BITS))
			       * 1000000 / 3321928)
	+ 2;			/* 2 :: guard digits.  */
#endif

      if (number_of_digits_available > maximum_useful_digits)
	{
	  number_of_digits_to_use = maximum_useful_digits;
	}
      else
	{
	  number_of_digits_to_use = number_of_digits_available;
	}

      /* Cast these to SIGNED LONG first, otherwise, on systems with
	 LONG wider than INT (such as Alpha OSF/1), unsignedness may
	 cause unexpected results.  */
      decimal_exponent += ((long) number_of_digits_before_decimal
			   - (long) number_of_digits_to_use);

#if 0
      more_than_enough_bits_for_digits
	= ((((double) number_of_digits_to_use) * LOG_TO_BASE_2_OF_10) + 1);
#else
      more_than_enough_bits_for_digits
	= (number_of_digits_to_use * 3321928 / 1000000 + 1);
#endif

      more_than_enough_littlenums_for_digits
	= (more_than_enough_bits_for_digits
	   / LITTLENUM_NUMBER_OF_BITS)
	+ 2;

      /* Compute (digits) part. In "12.34E56" this is the "1234" part.
	 Arithmetic is exact here. If no digits are supplied then this
	 part is a 0 valued binary integer.  Allocate room to build up
	 the binary number as littlenums.  We want this memory to
	 disappear when we leave this function.  Assume no alignment
	 problems => (room for n objects) == n * (room for 1
	 object).  */

      size_of_digits_in_littlenums = more_than_enough_littlenums_for_digits;
      size_of_digits_in_chars = size_of_digits_in_littlenums
	* sizeof (LITTLENUM_TYPE);

      digits_binary_low = (LITTLENUM_TYPE *)
	alloca (size_of_digits_in_chars);

      memset ((char *) digits_binary_low, '\0', size_of_digits_in_chars);

      /* Digits_binary_low[] is allocated and zeroed.  */

      /*
       * Parse the decimal digits as if * digits_low was in the units position.
       * Emit a binary number into digits_binary_low[].
       *
       * Use a large-precision version of:
       * (((1st-digit) * 10 + 2nd-digit) * 10 + 3rd-digit ...) * 10 + last-digit
       */

      for (p = first_digit, count = number_of_digits_to_use; count; p++, --count)
	{
	  c = *p;
	  if (isdigit ((unsigned char) c))
	    {
	      /*
	       * Multiply by 10. Assume can never overflow.
	       * Add this digit to digits_binary_low[].
	       */

	      long carry;
	      LITTLENUM_TYPE *littlenum_pointer;
	      LITTLENUM_TYPE *littlenum_limit;

	      littlenum_limit = digits_binary_low
		+ more_than_enough_littlenums_for_digits
		- 1;

	      carry = c - '0';	/* char -> binary */

	      for (littlenum_pointer = digits_binary_low;
		   littlenum_pointer <= littlenum_limit;
		   littlenum_pointer++)
		{
		  long work;

		  work = carry + 10 * (long) (*littlenum_pointer);
		  *littlenum_pointer = work & LITTLENUM_MASK;
		  carry = work >> LITTLENUM_NUMBER_OF_BITS;
		}

	      if (carry != 0)
		{
		  /*
		   * We have a GROSS internal error.
		   * This should never happen.
		   */
		  as_fatal (_("failed sanity check."));
		}
	    }
	  else
	    {
	      ++count;		/* '.' doesn't alter digits used count.  */
	    }
	}

      /*
       * Digits_binary_low[] properly encodes the value of the digits.
       * Forget about any high-order littlenums that are 0.
       */
      while (digits_binary_low[size_of_digits_in_littlenums - 1] == 0
	     && size_of_digits_in_littlenums >= 2)
	size_of_digits_in_littlenums--;

      digits_flonum.low = digits_binary_low;
      digits_flonum.high = digits_binary_low + size_of_digits_in_littlenums - 1;
      digits_flonum.leader = digits_flonum.high;
      digits_flonum.exponent = 0;
      /*
       * The value of digits_flonum . sign should not be important.
       * We have already decided the output's sign.
       * We trust that the sign won't influence the other parts of the number!
       * So we give it a value for these reasons:
       * (1) courtesy to humans reading/debugging
       *     these numbers so they don't get excited about strange values
       * (2) in future there may be more meaning attached to sign,
       *     and what was
       *     harmless noise may become disruptive, ill-conditioned (or worse)
       *     input.
       */
      digits_flonum.sign = '+';

      {
	/*
	 * Compute the mantssa (& exponent) of the power of 10.
	 * If sucessful, then multiply the power of 10 by the digits
	 * giving return_binary_mantissa and return_binary_exponent.
	 */

	LITTLENUM_TYPE *power_binary_low;
	int decimal_exponent_is_negative;
	/* This refers to the "-56" in "12.34E-56".  */
	/* FALSE: decimal_exponent is positive (or 0) */
	/* TRUE:  decimal_exponent is negative */
	FLONUM_TYPE temporary_flonum;
	LITTLENUM_TYPE *temporary_binary_low;
	unsigned int size_of_power_in_littlenums;
	unsigned int size_of_power_in_chars;

	size_of_power_in_littlenums = precision;
	/* Precision has a built-in fudge factor so we get a few guard bits.  */

	decimal_exponent_is_negative = decimal_exponent < 0;
	if (decimal_exponent_is_negative)
	  {
	    decimal_exponent = -decimal_exponent;
	  }

	/* From now on: the decimal exponent is > 0. Its sign is separate.  */

	size_of_power_in_chars = size_of_power_in_littlenums
	  * sizeof (LITTLENUM_TYPE) + 2;

	power_binary_low = (LITTLENUM_TYPE *) alloca (size_of_power_in_chars);
	temporary_binary_low = (LITTLENUM_TYPE *) alloca (size_of_power_in_chars);
	memset ((char *) power_binary_low, '\0', size_of_power_in_chars);
	*power_binary_low = 1;
	power_of_10_flonum.exponent = 0;
	power_of_10_flonum.low = power_binary_low;
	power_of_10_flonum.leader = power_binary_low;
	power_of_10_flonum.high = power_binary_low + size_of_power_in_littlenums - 1;
	power_of_10_flonum.sign = '+';
	temporary_flonum.low = temporary_binary_low;
	temporary_flonum.high = temporary_binary_low + size_of_power_in_littlenums - 1;
	/*
	 * (power) == 1.
	 * Space for temporary_flonum allocated.
	 */

	/*
	 * ...
	 *
	 * WHILE	more bits
	 * DO	find next bit (with place value)
	 *	multiply into power mantissa
	 * OD
	 */
	{
	  int place_number_limit;
	  /* Any 10^(2^n) whose "n" exceeds this */
	  /* value will fall off the end of */
	  /* flonum_XXXX_powers_of_ten[].  */
	  int place_number;
	  const FLONUM_TYPE *multiplicand;	/* -> 10^(2^n) */

	  place_number_limit = table_size_of_flonum_powers_of_ten;

	  multiplicand = (decimal_exponent_is_negative
			  ? flonum_negative_powers_of_ten
			  : flonum_positive_powers_of_ten);

	  for (place_number = 1;/* Place value of this bit of exponent.  */
	       decimal_exponent;/* Quit when no more 1 bits in exponent.  */
	       decimal_exponent >>= 1, place_number++)
	    {
	      if (decimal_exponent & 1)
		{
		  if (place_number > place_number_limit)
		    {
		      /* The decimal exponent has a magnitude so great
			 that our tables can't help us fragment it.
			 Although this routine is in error because it
			 can't imagine a number that big, signal an
			 error as if it is the user's fault for
			 presenting such a big number.  */
		      return_value = ERROR_EXPONENT_OVERFLOW;
		      /* quit out of loop gracefully */
		      decimal_exponent = 0;
		    }
		  else
		    {
#ifdef TRACE
		      printf ("before multiply, place_number = %d., power_of_10_flonum:\n",
			      place_number);

		      flonum_print (&power_of_10_flonum);
		      (void) putchar ('\n');
#endif
#ifdef TRACE
		      printf ("multiplier:\n");
		      flonum_print (multiplicand + place_number);
		      (void) putchar ('\n');
#endif
		      flonum_multip (multiplicand + place_number,
				     &power_of_10_flonum, &temporary_flonum);
#ifdef TRACE
		      printf ("after multiply:\n");
		      flonum_print (&temporary_flonum);
		      (void) putchar ('\n');
#endif
		      flonum_copy (&temporary_flonum, &power_of_10_flonum);
#ifdef TRACE
		      printf ("after copy:\n");
		      flonum_print (&power_of_10_flonum);
		      (void) putchar ('\n');
#endif
		    } /* If this bit of decimal_exponent was computable.*/
		} /* If this bit of decimal_exponent was set.  */
	    } /* For each bit of binary representation of exponent */
#ifdef TRACE
	  printf ("after computing power_of_10_flonum:\n");
	  flonum_print (&power_of_10_flonum);
	  (void) putchar ('\n');
#endif
	}

      }

      /*
       * power_of_10_flonum is power of ten in binary (mantissa) , (exponent).
       * It may be the number 1, in which case we don't NEED to multiply.
       *
       * Multiply (decimal digits) by power_of_10_flonum.
       */

      flonum_multip (&power_of_10_flonum, &digits_flonum, address_of_generic_floating_point_number);
      /* Assert sign of the number we made is '+'.  */
      address_of_generic_floating_point_number->sign = digits_sign_char;

    }
  return return_value;
}

#ifdef TRACE
static void
flonum_print (f)
     const FLONUM_TYPE *f;
{
  LITTLENUM_TYPE *lp;
  char littlenum_format[10];
  sprintf (littlenum_format, " %%0%dx", sizeof (LITTLENUM_TYPE) * 2);
#define print_littlenum(LP)	(printf (littlenum_format, LP))
  printf ("flonum @%p %c e%ld", f, f->sign, f->exponent);
  if (f->low < f->high)
    for (lp = f->high; lp >= f->low; lp--)
      print_littlenum (*lp);
  else
    for (lp = f->low; lp <= f->high; lp++)
      print_littlenum (*lp);
  printf ("\n");
  fflush (stdout);
}
#endif

/* end of atof_generic.c */