source: trunk/third/gcc/config/fp-bit.c @ 8834

/* This is a software floating point library which can be used instead of
   the floating point routines in libgcc1.c for targets without hardware
   floating point.  */

/* Copyright (C) 1994, 1995 Free Software Foundation, Inc.

This file is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2, or (at your option) any
later version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file with other programs, and to distribute
those programs without any restriction coming from the use of this
file.  (The General Public License restrictions do apply in other
respects; for example, they cover modification of the file, and
distribution when not linked into another program.)

This file is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* As a special exception, if you link this library with other files,
   some of which are compiled with GCC, to produce an executable,
   this library does not by itself cause the resulting executable
   to be covered by the GNU General Public License.
   This exception does not however invalidate any other reasons why
   the executable file might be covered by the GNU General Public License.  */

/* This implements IEEE 754 format arithmetic, but does not provide a
   mechanism for setting the rounding mode, or for generating or handling
   exceptions.

   The original code by Steve Chamberlain, hacked by Mark Eichin and Jim
   Wilson, all of Cygnus Support.  */

/* The intended way to use this file is to make two copies, add `#define FLOAT'
   to one copy, then compile both copies and add them to libgcc.a.  */

/* The following macros can be defined to change the behaviour of this file:
   FLOAT: Implement a `float', aka SFmode, fp library.  If this is not
     defined, then this file implements a `double', aka DFmode, fp library.
   FLOAT_ONLY: Used with FLOAT, to implement a `float' only library, i.e.
     don't include float->double conversion which requires the double library.
     This is useful only for machines which can't support doubles, e.g. some
     8-bit processors.
   CMPtype: Specify the type that floating point compares should return.
     This defaults to SItype, aka int.
   US_SOFTWARE_GOFAST: This makes all entry points use the same names as the
     US Software goFast library.  If this is not defined, the entry points use
     the same names as libgcc1.c.
   _DEBUG_BITFLOAT: This makes debugging the code a little easier, by adding
     two integers to the FLO_union_type.  
   NO_NANS: Disable nan and infinity handling
   SMALL_MACHINE: Useful when operations on QIs and HIs are faster
     than on an SI */

typedef SFtype __attribute__ ((mode (SF)));
typedef DFtype __attribute__ ((mode (DF)));

typedef int HItype __attribute__ ((mode (HI)));
typedef int SItype __attribute__ ((mode (SI)));
typedef int DItype __attribute__ ((mode (DI)));

/* The type of the result of a fp compare */
#ifndef CMPtype
#define CMPtype SItype
#endif

typedef unsigned int UHItype __attribute__ ((mode (HI)));
typedef unsigned int USItype __attribute__ ((mode (SI)));
typedef unsigned int UDItype __attribute__ ((mode (DI)));

#define MAX_SI_INT   ((SItype) ((unsigned) (~0)>>1))
#define MAX_USI_INT  ((USItype) ~0)


#ifdef FLOAT_ONLY
#define NO_DI_MODE
#endif

#ifdef FLOAT
#       define NGARDS    7L
#       define GARDROUND 0x3f
#       define GARDMASK  0x7f
#       define GARDMSB   0x40
#       define EXPBITS 8
#       define EXPBIAS 127
#       define FRACBITS 23
#       define EXPMAX (0xff)
#       define QUIET_NAN 0x100000L
#       define FRAC_NBITS 32
#       define FRACHIGH  0x80000000L
#       define FRACHIGH2 0xc0000000L
#       define pack_d pack_f
#       define unpack_d unpack_f
        typedef USItype fractype;
        typedef UHItype halffractype;
        typedef SFtype FLO_type;
        typedef SItype intfrac;

#else
#       define PREFIXFPDP dp
#       define PREFIXSFDF df
#       define NGARDS 8L
#       define GARDROUND 0x7f
#       define GARDMASK  0xff
#       define GARDMSB   0x80
#       define EXPBITS 11
#       define EXPBIAS 1023
#       define FRACBITS 52
#       define EXPMAX (0x7ff)
#       define QUIET_NAN 0x8000000000000LL
#       define FRAC_NBITS 64
#       define FRACHIGH  0x8000000000000000LL
#       define FRACHIGH2 0xc000000000000000LL
        typedef UDItype fractype;
        typedef USItype halffractype;
        typedef DFtype FLO_type;
        typedef DItype intfrac;
#endif

#ifdef US_SOFTWARE_GOFAST
#       ifdef FLOAT
#               define add              fpadd
#               define sub              fpsub
#               define multiply         fpmul
#               define divide           fpdiv
#               define compare          fpcmp
#               define si_to_float      sitofp
#               define float_to_si      fptosi
#               define float_to_usi     fptoui
#               define negate           __negsf2
#               define sf_to_df         fptodp
#               define dptofp           dptofp
#else
#               define add              dpadd
#               define sub              dpsub
#               define multiply         dpmul
#               define divide           dpdiv
#               define compare          dpcmp
#               define si_to_float      litodp
#               define float_to_si      dptoli
#               define float_to_usi     dptoul
#               define negate           __negdf2
#               define df_to_sf         dptofp
#endif
#else
#       ifdef FLOAT
#               define add              __addsf3
#               define sub              __subsf3
#               define multiply         __mulsf3
#               define divide           __divsf3
#               define compare          __cmpsf2
#               define _eq_f2           __eqsf2
#               define _ne_f2           __nesf2
#               define _gt_f2           __gtsf2
#               define _ge_f2           __gesf2
#               define _lt_f2           __ltsf2
#               define _le_f2           __lesf2
#               define si_to_float      __floatsisf
#               define float_to_si      __fixsfsi
#               define float_to_usi     __fixunssfsi
#               define negate           __negsf2
#               define sf_to_df         __extendsfdf2
#else
#               define add              __adddf3
#               define sub              __subdf3
#               define multiply         __muldf3
#               define divide           __divdf3
#               define compare          __cmpdf2
#               define _eq_f2           __eqdf2
#               define _ne_f2           __nedf2
#               define _gt_f2           __gtdf2
#               define _ge_f2           __gedf2
#               define _lt_f2           __ltdf2
#               define _le_f2           __ledf2
#               define si_to_float      __floatsidf
#               define float_to_si      __fixdfsi
#               define float_to_usi     __fixunsdfsi
#               define negate           __negdf2
#               define df_to_sf         __truncdfsf2
#       endif
#endif


#define INLINE __inline__

/* Preserve the sticky-bit when shifting fractions to the right.  */
#define LSHIFT(a) { a = (a & 1) | (a >> 1); }

/* numeric parameters */
/* F_D_BITOFF is the number of bits offset between the MSB of the mantissa
   of a float and of a double. Assumes there are only two float types.
   (double::FRAC_BITS+double::NGARGS-(float::FRAC_BITS-float::NGARDS))
 */
#define F_D_BITOFF (52+8-(23+7))


#define NORMAL_EXPMIN (-(EXPBIAS)+1)
#define IMPLICIT_1 (1LL<<(FRACBITS+NGARDS))
#define IMPLICIT_2 (1LL<<(FRACBITS+1+NGARDS))

/* common types */

typedef enum
{
  CLASS_SNAN,
  CLASS_QNAN,
  CLASS_ZERO,
  CLASS_NUMBER,
  CLASS_INFINITY
} fp_class_type;

typedef struct
{
#ifdef SMALL_MACHINE
  char class;
  unsigned char sign;
  short normal_exp;
#else
  fp_class_type class;
  unsigned int sign;
  int normal_exp;
#endif

  union
    {
      fractype ll;
      halffractype l[2];
    } fraction;
} fp_number_type;

typedef union
{
  FLO_type value;
  fractype value_raw;

#ifndef FLOAT
  halffractype words[2];
#endif

#ifdef FLOAT_BIT_ORDER_MISMATCH
  struct
    {
      fractype fraction:FRACBITS __attribute__ ((packed));
      unsigned int exp:EXPBITS __attribute__ ((packed));
      unsigned int sign:1 __attribute__ ((packed));
    }
  bits;
#endif

#ifdef _DEBUG_BITFLOAT
  struct
    {
      unsigned int sign:1 __attribute__ ((packed));
      unsigned int exp:EXPBITS __attribute__ ((packed));
      fractype fraction:FRACBITS __attribute__ ((packed));
    }
  bits_big_endian;

  struct
    {
      fractype fraction:FRACBITS __attribute__ ((packed));
      unsigned int exp:EXPBITS __attribute__ ((packed));
      unsigned int sign:1 __attribute__ ((packed));
    }
  bits_little_endian;
#endif
}
FLO_union_type;


/* end of header */

/* IEEE "special" number predicates */

#ifdef NO_NANS

#define nan() 0
#define isnan(x) 0
#define isinf(x) 0
#else

INLINE
static fp_number_type *
nan ()
{
  static fp_number_type thenan;

  return &thenan;
}

INLINE
static int
isnan ( fp_number_type *  x)
{
  return x->class == CLASS_SNAN || x->class == CLASS_QNAN;
}

INLINE
static int
isinf ( fp_number_type *  x)
{
  return x->class == CLASS_INFINITY;
}

#endif

INLINE
static int
iszero ( fp_number_type *  x)
{
  return x->class == CLASS_ZERO;
}

INLINE 
static void
flip_sign ( fp_number_type *  x)
{
  x->sign = !x->sign;
}

static FLO_type
pack_d ( fp_number_type *  src)
{
  FLO_union_type dst;
  fractype fraction = src->fraction.ll; /* wasn't unsigned before? */
  int sign = src->sign;
  int exp = 0;

  if (isnan (src))
    {
      exp = EXPMAX;
      if (src->class == CLASS_QNAN || 1)
        {
          fraction |= QUIET_NAN;
        }
    }
  else if (isinf (src))
    {
      exp = EXPMAX;
      fraction = 0;
    }
  else if (iszero (src))
    {
      exp = 0;
      fraction = 0;
    }
  else if (fraction == 0)
    {
      exp = 0;
      sign = 0;
    }
  else
    {
      if (src->normal_exp < NORMAL_EXPMIN)
        {
          /* This number's exponent is too low to fit into the bits
             available in the number, so we'll store 0 in the exponent and
             shift the fraction to the right to make up for it.  */

          int shift = NORMAL_EXPMIN - src->normal_exp;

          exp = 0;

          if (shift > FRAC_NBITS - NGARDS)
            {
              /* No point shifting, since it's more that 64 out.  */
              fraction = 0;
            }
          else
            {
              /* Shift by the value */
              fraction >>= shift;
            }
          fraction >>= NGARDS;
        }
      else if (src->normal_exp > EXPBIAS)
        {
          exp = EXPMAX;
          fraction = 0;
        }
      else
        {
          exp = src->normal_exp + EXPBIAS;
          /* IF the gard bits are the all zero, but the first, then we're
             half way between two numbers, choose the one which makes the
             lsb of the answer 0.  */
          if ((fraction & GARDMASK) == GARDMSB)
            {
              if (fraction & (1 << NGARDS))
                fraction += GARDROUND + 1;
            }
          else
            {
              /* Add a one to the guards to round up */
              fraction += GARDROUND;
            }
          if (fraction >= IMPLICIT_2)
            {
              fraction >>= 1;
              exp += 1;
            }
          fraction >>= NGARDS;
        }
    }

  /* We previously used bitfields to store the number, but this doesn't
     handle little/big endian systems conviently, so use shifts and
     masks */
#ifdef FLOAT_BIT_ORDER_MISMATCH
  dst.bits.fraction = fraction;
  dst.bits.exp = exp;
  dst.bits.sign = sign;
#else
  dst.value_raw = fraction & ((((fractype)1) << FRACBITS) - (fractype)1);
  dst.value_raw |= ((fractype) (exp & ((1 << EXPBITS) - 1))) << FRACBITS;
  dst.value_raw |= ((fractype) (sign & 1)) << (FRACBITS | EXPBITS);
#endif

#if defined(FLOAT_WORD_ORDER_MISMATCH) && !defined(FLOAT)
  {
    halffractype tmp = dst.words[0];
    dst.words[0] = dst.words[1];
    dst.words[1] = tmp;
  }
#endif

  return dst.value;
}

static void
unpack_d (FLO_union_type * src, fp_number_type * dst)
{
  /* We previously used bitfields to store the number, but this doesn't
     handle little/big endian systems conviently, so use shifts and
     masks */
  fractype fraction;
  int exp;
  int sign;

#if defined(FLOAT_WORD_ORDER_MISMATCH) && !defined(FLOAT)
  FLO_union_type swapped;

  swapped.words[0] = src->words[1];
  swapped.words[1] = src->words[0];
  src = &swapped;
#endif
  
#ifdef FLOAT_BIT_ORDER_MISMATCH
  fraction = src->bits.fraction;
  exp = src->bits.exp;
  sign = src->bits.sign;
#else
  fraction = src->value_raw & ((((fractype)1) << FRACBITS) - (fractype)1);
  exp = ((int)(src->value_raw >> FRACBITS)) & ((1 << EXPBITS) - 1);
  sign = ((int)(src->value_raw >> (FRACBITS + EXPBITS))) & 1;
#endif

  dst->sign = sign;
  if (exp == 0)
    {
      /* Hmm.  Looks like 0 */
      if (fraction == 0)
        {
          /* tastes like zero */
          dst->class = CLASS_ZERO;
        }
      else
        {
          /* Zero exponent with non zero fraction - it's denormalized,
             so there isn't a leading implicit one - we'll shift it so
             it gets one.  */
          dst->normal_exp = exp - EXPBIAS + 1;
          fraction <<= NGARDS;

          dst->class = CLASS_NUMBER;
#if 1
          while (fraction < IMPLICIT_1)
            {
              fraction <<= 1;
              dst->normal_exp--;
            }
#endif
          dst->fraction.ll = fraction;
        }
    }
  else if (exp == EXPMAX)
    {
      /* Huge exponent*/
      if (fraction == 0)
        {
          /* Attached to a zero fraction - means infinity */
          dst->class = CLASS_INFINITY;
        }
      else
        {
          /* Non zero fraction, means nan */
          if (sign)
            {
              dst->class = CLASS_SNAN;
            }
          else
            {
              dst->class = CLASS_QNAN;
            }
          /* Keep the fraction part as the nan number */
          dst->fraction.ll = fraction;
        }
    }
  else
    {
      /* Nothing strange about this number */
      dst->normal_exp = exp - EXPBIAS;
      dst->class = CLASS_NUMBER;
      dst->fraction.ll = (fraction << NGARDS) | IMPLICIT_1;
    }
}

static fp_number_type *
_fpadd_parts (fp_number_type * a,
              fp_number_type * b,
              fp_number_type * tmp)
{
  intfrac tfraction;

  /* Put commonly used fields in local variables.  */
  int a_normal_exp;
  int b_normal_exp;
  fractype a_fraction;
  fractype b_fraction;

  if (isnan (a))
    {
      return a;
    }
  if (isnan (b))
    {
      return b;
    }
  if (isinf (a))
    {
      /* Adding infinities with opposite signs yields a NaN.  */
      if (isinf (b) && a->sign != b->sign)
        return nan ();
      return a;
    }
  if (isinf (b))
    {
      return b;
    }
  if (iszero (b))
    {
      return a;
    }
  if (iszero (a))
    {
      return b;
    }

  /* Got two numbers. shift the smaller and increment the exponent till
     they're the same */
  {
    int diff;

    a_normal_exp = a->normal_exp;
    b_normal_exp = b->normal_exp;
    a_fraction = a->fraction.ll;
    b_fraction = b->fraction.ll;

    diff = a_normal_exp - b_normal_exp;

    if (diff < 0)
      diff = -diff;
    if (diff < FRAC_NBITS)
      {
        /* ??? This does shifts one bit at a time.  Optimize.  */
        while (a_normal_exp > b_normal_exp)
          {
            b_normal_exp++;
            LSHIFT (b_fraction);
          }
        while (b_normal_exp > a_normal_exp)
          {
            a_normal_exp++;
            LSHIFT (a_fraction);
          }
      }
    else
      {
        /* Somethings's up.. choose the biggest */
        if (a_normal_exp > b_normal_exp)
          {
            b_normal_exp = a_normal_exp;
            b_fraction = 0;
          }
        else
          {
            a_normal_exp = b_normal_exp;
            a_fraction = 0;
          }
      }
  }

  if (a->sign != b->sign)
    {
      if (a->sign)
        {
          tfraction = -a_fraction + b_fraction;
        }
      else
        {
          tfraction = a_fraction - b_fraction;
        }
      if (tfraction > 0)
        {
          tmp->sign = 0;
          tmp->normal_exp = a_normal_exp;
          tmp->fraction.ll = tfraction;
        }
      else
        {
          tmp->sign = 1;
          tmp->normal_exp = a_normal_exp;
          tmp->fraction.ll = -tfraction;
        }
      /* and renormalize it */

      while (tmp->fraction.ll < IMPLICIT_1 && tmp->fraction.ll)
        {
          tmp->fraction.ll <<= 1;
          tmp->normal_exp--;
        }
    }
  else
    {
      tmp->sign = a->sign;
      tmp->normal_exp = a_normal_exp;
      tmp->fraction.ll = a_fraction + b_fraction;
    }
  tmp->class = CLASS_NUMBER;
  /* Now the fraction is added, we have to shift down to renormalize the
     number */

  if (tmp->fraction.ll >= IMPLICIT_2)
    {
      LSHIFT (tmp->fraction.ll);
      tmp->normal_exp++;
    }
  return tmp;

}

FLO_type
add (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;
  fp_number_type tmp;
  fp_number_type *res;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  res = _fpadd_parts (&a, &b, &tmp);

  return pack_d (res);
}

FLO_type
sub (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;
  fp_number_type tmp;
  fp_number_type *res;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  b.sign ^= 1;

  res = _fpadd_parts (&a, &b, &tmp);

  return pack_d (res);
}

static fp_number_type *
_fpmul_parts ( fp_number_type *  a,
               fp_number_type *  b,
               fp_number_type * tmp)
{
  fractype low = 0;
  fractype high = 0;

  if (isnan (a))
    {
      a->sign = a->sign != b->sign;
      return a;
    }
  if (isnan (b))
    {
      b->sign = a->sign != b->sign;
      return b;
    }
  if (isinf (a))
    {
      if (iszero (b))
        return nan ();
      a->sign = a->sign != b->sign;
      return a;
    }
  if (isinf (b))
    {
      if (iszero (a))
        {
          return nan ();
        }
      b->sign = a->sign != b->sign;
      return b;
    }
  if (iszero (a))
    {
      a->sign = a->sign != b->sign;
      return a;
    }
  if (iszero (b))
    {
      b->sign = a->sign != b->sign;
      return b;
    }

  /* Calculate the mantissa by multiplying both 64bit numbers to get a
     128 bit number */
  {
    fractype x = a->fraction.ll;
    fractype ylow = b->fraction.ll;
    fractype yhigh = 0;
    int bit;

#if defined(NO_DI_MODE)
    {
      /* ??? This does multiplies one bit at a time.  Optimize.  */
      for (bit = 0; bit < FRAC_NBITS; bit++)
        {
          int carry;

          if (x & 1)
            {
              carry = (low += ylow) < ylow;
              high += yhigh + carry;
            }
          yhigh <<= 1;
          if (ylow & FRACHIGH)
            {
              yhigh |= 1;
            }
          ylow <<= 1;
          x >>= 1;
        }
    }
#elif defined(FLOAT) 
    {
      /* Multiplying two 32 bit numbers to get a 64 bit number  on 
        a machine with DI, so we're safe */

      DItype answer = (DItype)(a->fraction.ll) * (DItype)(b->fraction.ll);
      
      high = answer >> 32;
      low = answer;
    }
#else
    /* Doing a 64*64 to 128 */
    {
      UDItype nl = a->fraction.ll & 0xffffffff;
      UDItype nh = a->fraction.ll >> 32;
      UDItype ml = b->fraction.ll & 0xffffffff;
      UDItype mh = b->fraction.ll >>32;
      UDItype pp_ll = ml * nl;
      UDItype pp_hl = mh * nl;
      UDItype pp_lh = ml * nh;
      UDItype pp_hh = mh * nh;
      UDItype res2 = 0;
      UDItype res0 = 0;
      UDItype ps_hh__ = pp_hl + pp_lh;
      if (ps_hh__ < pp_hl)
        res2 += 0x100000000LL;
      pp_hl = (ps_hh__ << 32) & 0xffffffff00000000LL;
      res0 = pp_ll + pp_hl;
      if (res0 < pp_ll)
        res2++;
      res2 += ((ps_hh__ >> 32) & 0xffffffffL) + pp_hh;
      high = res2;
      low = res0;
    }
#endif
  }

  tmp->normal_exp = a->normal_exp + b->normal_exp;
  tmp->sign = a->sign != b->sign;
#ifdef FLOAT
  tmp->normal_exp += 2;         /* ??????????????? */
#else
  tmp->normal_exp += 4;         /* ??????????????? */
#endif
  while (high >= IMPLICIT_2)
    {
      tmp->normal_exp++;
      if (high & 1)
        {
          low >>= 1;
          low |= FRACHIGH;
        }
      high >>= 1;
    }
  while (high < IMPLICIT_1)
    {
      tmp->normal_exp--;

      high <<= 1;
      if (low & FRACHIGH)
        high |= 1;
      low <<= 1;
    }
  /* rounding is tricky. if we only round if it won't make us round later. */
#if 0
  if (low & FRACHIGH2)
    {
      if (((high & GARDMASK) != GARDMSB)
          && (((high + 1) & GARDMASK) == GARDMSB))
        {
          /* don't round, it gets done again later. */
        }
      else
        {
          high++;
        }
    }
#endif
  if ((high & GARDMASK) == GARDMSB)
    {
      if (high & (1 << NGARDS))
        {
          /* half way, so round to even */
          high += GARDROUND + 1;
        }
      else if (low)
        {
          /* but we really weren't half way */
          high += GARDROUND + 1;
        }
    }
  tmp->fraction.ll = high;
  tmp->class = CLASS_NUMBER;
  return tmp;
}

FLO_type
multiply (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;
  fp_number_type tmp;
  fp_number_type *res;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  res = _fpmul_parts (&a, &b, &tmp);

  return pack_d (res);
}

static fp_number_type *
_fpdiv_parts (fp_number_type * a,
              fp_number_type * b,
              fp_number_type * tmp)
{
  fractype low = 0;
  fractype high = 0;
  fractype r0, r1, y0, y1, bit;
  fractype q;
  fractype numerator;
  fractype denominator;
  fractype quotient;
  fractype remainder;

  if (isnan (a))
    {
      return a;
    }
  if (isnan (b))
    {
      return b;
    }
  if (isinf (a) || iszero (a))
    {
      if (a->class == b->class)
        return nan ();
      return a;
    }
  a->sign = a->sign ^ b->sign;

  if (isinf (b))
    {
      a->fraction.ll = 0;
      a->normal_exp = 0;
      return a;
    }
  if (iszero (b))
    {
      a->class = CLASS_INFINITY;
      return b;
    }

  /* Calculate the mantissa by multiplying both 64bit numbers to get a
     128 bit number */
  {
    int carry;
    intfrac d0, d1;             /* weren't unsigned before ??? */

    /* quotient =
       ( numerator / denominator) * 2^(numerator exponent -  denominator exponent)
     */

    a->normal_exp = a->normal_exp - b->normal_exp;
    numerator = a->fraction.ll;
    denominator = b->fraction.ll;

    if (numerator < denominator)
      {
        /* Fraction will be less than 1.0 */
        numerator *= 2;
        a->normal_exp--;
      }
    bit = IMPLICIT_1;
    quotient = 0;
    /* ??? Does divide one bit at a time.  Optimize.  */
    while (bit)
      {
        if (numerator >= denominator)
          {
            quotient |= bit;
            numerator -= denominator;
          }
        bit >>= 1;
        numerator *= 2;
      }

    if ((quotient & GARDMASK) == GARDMSB)
      {
        if (quotient & (1 << NGARDS))
          {
            /* half way, so round to even */
            quotient += GARDROUND + 1;
          }
        else if (numerator)
          {
            /* but we really weren't half way, more bits exist */
            quotient += GARDROUND + 1;
          }
      }

    a->fraction.ll = quotient;
    return (a);
  }
}

FLO_type
divide (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;
  fp_number_type tmp;
  fp_number_type *res;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  res = _fpdiv_parts (&a, &b, &tmp);

  return pack_d (res);
}

/* according to the demo, fpcmp returns a comparison with 0... thus
   a<b -> -1
   a==b -> 0
   a>b -> +1
 */

static int
_fpcmp_parts (fp_number_type * a, fp_number_type * b)
{
#if 0
  /* either nan -> unordered. Must be checked outside of this routine. */
  if (isnan (a) && isnan (b))
    {
      return 1;                 /* still unordered! */
    }
#endif

  if (isnan (a) || isnan (b))
    {
      return 1;                 /* how to indicate unordered compare? */
    }
  if (isinf (a) && isinf (b))
    {
      /* +inf > -inf, but +inf != +inf */
      /* b    \a| +inf(0)| -inf(1)
       ______\+--------+--------
       +inf(0)| a==b(0)| a<b(-1)
       -------+--------+--------
       -inf(1)| a>b(1) | a==b(0)
       -------+--------+--------
       So since unordered must be non zero, just line up the columns...
       */
      return b->sign - a->sign;
    }
  /* but not both... */
  if (isinf (a))
    {
      return a->sign ? -1 : 1;
    }
  if (isinf (b))
    {
      return b->sign ? 1 : -1;
    }
  if (iszero (a) && iszero (b))
    {
      return 0;
    }
  if (iszero (a))
    {
      return b->sign ? 1 : -1;
    }
  if (iszero (b))
    {
      return a->sign ? -1 : 1;
    }
  /* now both are "normal". */
  if (a->sign != b->sign)
    {
      /* opposite signs */
      return a->sign ? -1 : 1;
    }
  /* same sign; exponents? */
  if (a->normal_exp > b->normal_exp)
    {
      return a->sign ? -1 : 1;
    }
  if (a->normal_exp < b->normal_exp)
    {
      return a->sign ? 1 : -1;
    }
  /* same exponents; check size. */
  if (a->fraction.ll > b->fraction.ll)
    {
      return a->sign ? -1 : 1;
    }
  if (a->fraction.ll < b->fraction.ll)
    {
      return a->sign ? 1 : -1;
    }
  /* after all that, they're equal. */
  return 0;
}

CMPtype
compare (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  return _fpcmp_parts (&a, &b);
}

#ifndef US_SOFTWARE_GOFAST

/* These should be optimized for their specific tasks someday.  */

CMPtype
_eq_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return 1;                   /* false, truth == 0 */

  return _fpcmp_parts (&a, &b) ;
}

CMPtype
_ne_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return 1;                   /* true, truth != 0 */

  return  _fpcmp_parts (&a, &b) ;
}

CMPtype
_gt_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return -1;                  /* false, truth > 0 */

  return _fpcmp_parts (&a, &b);
}

CMPtype
_ge_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return -1;                  /* false, truth >= 0 */
  return _fpcmp_parts (&a, &b) ;
}

CMPtype
_lt_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return 1;                   /* false, truth < 0 */

  return _fpcmp_parts (&a, &b);
}

CMPtype
_le_f2 (FLO_type arg_a, FLO_type arg_b)
{
  fp_number_type a;
  fp_number_type b;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  unpack_d ((FLO_union_type *) & arg_b, &b);

  if (isnan (&a) || isnan (&b))
    return 1;                   /* false, truth <= 0 */

  return _fpcmp_parts (&a, &b) ;
}

#endif /* ! US_SOFTWARE_GOFAST */

FLO_type
si_to_float (SItype arg_a)
{
  fp_number_type in;

  in.class = CLASS_NUMBER;
  in.sign = arg_a < 0;
  if (!arg_a)
    {
      in.class = CLASS_ZERO;
    }
  else
    {
      in.normal_exp = FRACBITS + NGARDS;
      if (in.sign) 
        {
          /* Special case for minint, since there is no +ve integer
             representation for it */
          if (arg_a == 0x80000000)
            {
              return -2147483648.0;
            }
          in.fraction.ll = (-arg_a);
        }
      else
        in.fraction.ll = arg_a;

      while (in.fraction.ll < (1LL << (FRACBITS + NGARDS)))
        {
          in.fraction.ll <<= 1;
          in.normal_exp -= 1;
        }
    }
  return pack_d (&in);
}

SItype
float_to_si (FLO_type arg_a)
{
  fp_number_type a;
  SItype tmp;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  if (iszero (&a))
    return 0;
  if (isnan (&a))
    return 0;
  /* get reasonable MAX_SI_INT... */
  if (isinf (&a))
    return a.sign ? MAX_SI_INT : (-MAX_SI_INT)-1;
  /* it is a number, but a small one */
  if (a.normal_exp < 0)
    return 0;
  if (a.normal_exp > 30)
    return a.sign ? (-MAX_SI_INT)-1 : MAX_SI_INT;
  tmp = a.fraction.ll >> ((FRACBITS + NGARDS) - a.normal_exp);
  return a.sign ? (-tmp) : (tmp);
}

#ifdef US_SOFTWARE_GOFAST
/* While libgcc2.c defines its own __fixunssfsi and __fixunsdfsi routines,
   we also define them for GOFAST because the ones in libgcc2.c have the
   wrong names and I'd rather define these here and keep GOFAST CYG-LOC's
   out of libgcc2.c.  We can't define these here if not GOFAST because then
   there'd be duplicate copies.  */

USItype
float_to_usi (FLO_type arg_a)
{
  fp_number_type a;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  if (iszero (&a))
    return 0;
  if (isnan (&a))
    return 0;
  /* get reasonable MAX_USI_INT... */
  if (isinf (&a))
    return a.sign ? MAX_USI_INT : 0;
  /* it is a negative number */
  if (a.sign)
    return 0;
  /* it is a number, but a small one */
  if (a.normal_exp < 0)
    return 0;
  if (a.normal_exp > 31)
    return MAX_USI_INT;
  else if (a.normal_exp > (FRACBITS + NGARDS))
    return a.fraction.ll << ((FRACBITS + NGARDS) - a.normal_exp);
  else
    return a.fraction.ll >> ((FRACBITS + NGARDS) - a.normal_exp);
}
#endif

FLO_type
negate (FLO_type arg_a)
{
  fp_number_type a;

  unpack_d ((FLO_union_type *) & arg_a, &a);
  flip_sign (&a);
  return pack_d (&a);
}

#ifdef FLOAT

SFtype
__make_fp(fp_class_type class,
             unsigned int sign,
             int exp, 
             USItype frac)
{
  fp_number_type in;

  in.class = class;
  in.sign = sign;
  in.normal_exp = exp;
  in.fraction.ll = frac;
  return pack_d (&in);
}

#ifndef FLOAT_ONLY

/* This enables one to build an fp library that supports float but not double.
   Otherwise, we would get an undefined reference to __make_dp.
   This is needed for some 8-bit ports that can't handle well values that
   are 8-bytes in size, so we just don't support double for them at all.  */

extern DFtype __make_dp (fp_class_type, unsigned int, int, UDItype frac);

DFtype
sf_to_df (SFtype arg_a)
{
  fp_number_type in;

  unpack_d ((FLO_union_type *) & arg_a, &in);
  return __make_dp (in.class, in.sign, in.normal_exp,
                    ((UDItype) in.fraction.ll) << F_D_BITOFF);
}

#endif
#endif

#ifndef FLOAT

extern SFtype __make_fp (fp_class_type, unsigned int, int, USItype);

DFtype
__make_dp (fp_class_type class, unsigned int sign, int exp, UDItype frac)
{
  fp_number_type in;

  in.class = class;
  in.sign = sign;
  in.normal_exp = exp;
  in.fraction.ll = frac;
  return pack_d (&in);
}

SFtype
df_to_sf (DFtype arg_a)
{
  fp_number_type in;

  unpack_d ((FLO_union_type *) & arg_a, &in);
  return __make_fp (in.class, in.sign, in.normal_exp,
                    in.fraction.ll >> F_D_BITOFF);
}

#endif