/* -----------------------------------------------------------------------------
 *
 * (c) Lennart Augustsson
 * (c) The GHC Team, 1998-2000
 *
 * Miscellaneous support for floating-point primitives
 *
 * ---------------------------------------------------------------------------*/

#include "PosixSource.h"
#include "Rts.h"

#include "StgPrimFloat.h"

#include <math.h>
#include <float.h>

#define IEEE_FLOATING_POINT 1

/*
 * Encoding and decoding Doubles.  Code based on the HBC code
 * (lib/fltcode.c).
 */

#if IEEE_FLOATING_POINT
#define MY_DMINEXP  ((DBL_MIN_EXP) - (DBL_MANT_DIG) - 1)
/* DMINEXP is defined in values.h on Linux (for example) */
#define DHIGHBIT 0x00100000
#define DMSBIT   0x80000000

#define MY_FMINEXP  ((FLT_MIN_EXP) - (FLT_MANT_DIG) - 1)
#define FHIGHBIT 0x00800000
#define FMSBIT   0x80000000
#endif

#if defined(WORDS_BIGENDIAN) || defined(FLOAT_WORDS_BIGENDIAN)
#define L 1
#define H 0
#else
#define L 0
#define H 1
#endif

#define __abs(a)		(( (a) >= 0 ) ? (a) : (-(a)))

StgDouble
__2Int_encodeDouble (I_ j_high, I_ j_low, I_ e)
{
  StgDouble r;
  
  /* assuming 32 bit ints */
  ASSERT(sizeof(int          ) == 4            );

  r = (StgDouble)((unsigned int)j_high);
  r *= 4294967296.0; /* exp2f(32); */
  r += (StgDouble)((unsigned int)j_low);
  
  /* Now raise to the exponent */
  if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
    r = ldexp(r, e);
  
  /* sign is encoded in the size */
  if (j_high < 0)
    r = -r;
  
  return r;
}

/* Special version for words */
StgDouble
__word_encodeDouble (W_ j, I_ e)
{
  StgDouble r;
  
  r = (StgDouble)j;
  
  /* Now raise to the exponent */
  if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
    r = ldexp(r, e);
  
  return r;
}

/* Special version for small Integers */
StgDouble
__int_encodeDouble (I_ j, I_ e)
{
  StgDouble r;
  
  r = (StgDouble)__abs(j);
  
  /* Now raise to the exponent */
  if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
    r = ldexp(r, e);
  
  /* sign is encoded in the size */
  if (j < 0)
    r = -r;
  
  return r;
}

/* Special version for small Integers */
StgFloat
__int_encodeFloat (I_ j, I_ e)
{
  StgFloat r;
  
  r = (StgFloat)__abs(j);
  
  /* Now raise to the exponent */
  if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
    r = ldexp(r, e);
  
  /* sign is encoded in the size */
  if (j < 0)
    r = -r;
  
  return r;
}

/* Special version for small positive Integers */
StgFloat
__word_encodeFloat (W_ j, I_ e)
{
  StgFloat r;
  
  r = (StgFloat)j;
  
  /* Now raise to the exponent */
  if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
    r = ldexp(r, e);
  
  return r;
}

/* This only supports IEEE floating point */

void
__decodeDouble_2Int (I_ *man_sign, W_ *man_high, W_ *man_low, I_ *exp, StgDouble dbl)
{
    /* Do some bit fiddling on IEEE */
    unsigned int low, high; 	     	/* assuming 32 bit ints */
    int sign, iexp;
    union { double d; unsigned int i[2]; } u;	/* assuming 32 bit ints, 64 bit double */

    ASSERT(sizeof(unsigned int ) == 4            );
    ASSERT(sizeof(dbl          ) == 8            );
    ASSERT(sizeof(dbl          ) == SIZEOF_DOUBLE);

    u.d = dbl;	    /* grab chunks of the double */
    low = u.i[L];
    high = u.i[H];

    if (low == 0 && (high & ~DMSBIT) == 0) {
	*man_low = 0;
	*man_high = 0;
	*exp = 0L;
    } else {
	iexp = ((high >> 20) & 0x7ff) + MY_DMINEXP;
	sign = high;

	high &= DHIGHBIT-1;
	if (iexp != MY_DMINEXP)	/* don't add hidden bit to denorms */
	    high |= DHIGHBIT;
	else {
	    iexp++;
	    /* A denorm, normalize the mantissa */
	    while (! (high & DHIGHBIT)) {
		high <<= 1;
		if (low & DMSBIT)
		    high++;
		low <<= 1;
		iexp--;
	    }
	}
        *exp = (I_) iexp;
	*man_low = low;
	*man_high = high;
	*man_sign = (sign < 0) ? -1 : 1;
    }
}

/* Convenient union types for checking the layout of IEEE 754 types -
   based on defs in GNU libc <ieee754.h>
*/

void
__decodeFloat_Int (I_ *man, I_ *exp, StgFloat flt)
{
    /* Do some bit fiddling on IEEE */
    int high, sign; 	    	    /* assuming 32 bit ints */
    union { float f; int i; } u;    /* assuming 32 bit float and int */

    ASSERT(sizeof(int          ) == 4            );
    ASSERT(sizeof(flt          ) == 4            );
    ASSERT(sizeof(flt          ) == SIZEOF_FLOAT );

    u.f = flt;	    /* grab the float */
    high = u.i;

    if ((high & ~FMSBIT) == 0) {
	*man = 0;
	*exp = 0;
    } else {
	*exp = ((high >> 23) & 0xff) + MY_FMINEXP;
	sign = high;

	high &= FHIGHBIT-1;
	if (*exp != MY_FMINEXP)	/* don't add hidden bit to denorms */
	    high |= FHIGHBIT;
	else {
	    (*exp)++;
	    /* A denorm, normalize the mantissa */
	    while (! (high & FHIGHBIT)) {
		high <<= 1;
		(*exp)--;
	    }
	}
	*man = high;
	if (sign < 0)
	    *man = - *man;
    }
}