integer-gmp-0.5.1.0: cbits/float.c
/* -----------------------------------------------------------------------------
*
* (c) Lennart Augustsson
* (c) The GHC Team, 1998-2000
*
* Support for floating-point <-> gmp integer primitives
*
* ---------------------------------------------------------------------------*/
/* TODO: do we need PosixSource.h ? it lives in rts/ not public includes/ */
/* #include "PosixSource.h" */
#include "Rts.h"
#include "gmp.h"
#include "GmpDerivedConstants.h"
#include <math.h>
#define IEEE_FLOATING_POINT 1
/*
* Encoding and decoding Doubles. Code based on the HBC code
* (lib/fltcode.c).
*/
#define SIZEOF_LIMB_T SIZEOF_MP_LIMB_T
#if SIZEOF_LIMB_T == 4
#define GMP_BASE 4294967296.0
#define LIMBBITS_LOG_2 5
#elif SIZEOF_LIMB_T == 8
#define GMP_BASE 18446744073709551616.0
#define LIMBBITS_LOG_2 6
#else
#error Cannot cope with SIZEOF_LIMB_T -- please add definition of GMP_BASE
#endif
#define DNBIGIT ((SIZEOF_DOUBLE+SIZEOF_LIMB_T-1)/SIZEOF_LIMB_T)
#define FNBIGIT ((SIZEOF_FLOAT +SIZEOF_LIMB_T-1)/SIZEOF_LIMB_T)
#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
integer_cbits_encodeDouble (I_ size, StgByteArray ba, I_ e) /* result = s * 2^e */
{
StgDouble r;
const mp_limb_t *const arr = (const mp_limb_t *)ba;
I_ i;
/* Convert MP_INT to a double; knows a lot about internal rep! */
i = __abs(size)-1;
if ((i < 15) || (e >= 0)) /* overflows only if the final result does */
{
/* This would cause overflow if a large MP_INT is passed, even if the
* exponent would scale it back into range, so we do it only when it's safe. */
for(r = 0.0; i >= 0; i--)
r = (r * GMP_BASE) + arr[i];
} else { /* possibly more than 1024 bits in the MP_INT, but gets scaled down */
/* Find the first nonzero limb; normally it would be the first */
r = 0.0;
while((i >= 0) && (r == 0.0))
{
r = arr[i--];
}
if (i >= 0)
r = (r * GMP_BASE) + arr[i];
#if SIZEOF_LIMB_T < 8
if (i > 0)
r = (r * GMP_BASE) + arr[--i];
#endif
/* Now we have at least the 65 leading bits of the MP_INT or all of it.
* Any further bits would be rounded down, so from now on everything is
* multiplication by powers of 2.
* If i is positive, arr contains i limbs we haven't looked at yet, so
* adjust the exponent by i*8*SIZEOF_LIMB_T. Unfortunately, we must
* beware of overflow, so we can't simply add this to e. */
if (i > 0)
{
/* first add the number of whole limbs that would be cancelled */
i = i + e / (8 * SIZEOF_LIMB_T);
/* check for overflow */
if ((i > 0) && ((i >> (8*sizeof(I_) - 1 - LIMBBITS_LOG_2)) > 0))
{
/* overflow, give e a large dummy value */
e = 2147483647;
} else {
/* no overflow, get the exact value */
e = i * (8 * SIZEOF_LIMB_T) + (e % (8 * SIZEOF_LIMB_T));
}
}
}
/* 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 (size < 0)
r = -r;
return r;
}
StgFloat
integer_cbits_encodeFloat (I_ size, StgByteArray ba, I_ e) /* result = s * 2^e */
{
StgFloat r;
const mp_limb_t *arr = (const mp_limb_t *)ba;
I_ i;
/* Convert MP_INT to a float; knows a lot about internal rep! */
i = __abs(size)-1;
/* just in case StgFloat is a double, check sizes */
#if SIZEOF_FLOAT == 4
if ((i < 2) || (e >= 0))
#else
if ((i < 15) || (e >= 0))
#endif
{
for(r = 0.0; i >= 0; i--)
r = (r * GMP_BASE) + arr[i];
} else {
/* Find the first nonzero limb; normally it would be the first */
r = 0.0;
while((i >= 0) && (r == 0.0))
{
r = arr[i--];
}
if (i >= 0)
r = (r * GMP_BASE) + arr[i];
#if (SIZEOF_LIMB_T < 8) && (SIZEOF_FLOAT > 4)
if (i > 0)
r = (r * GMP_BASE) + arr[--i];
#endif
/* Now we have enough leading bits of the MP_INT.
* Any further bits would be rounded down, so from now on everything is
* multiplication by powers of 2.
* If i is positive, arr contains i limbs we haven't looked at yet, so
* adjust the exponent by i*8*SIZEOF_LIMB_T. Unfortunately, we must
* beware of overflow, so we can't simply add this to e. */
if (i > 0)
{
/* first add the number of whole limbs that would be cancelled */
i = i + e / (8 * SIZEOF_LIMB_T);
/* check for overflow */
if ((i > 0) && ((i >> (8*sizeof(I_) - 1 - LIMBBITS_LOG_2)) > 0))
{
/* overflow, give e a large dummy value */
e = 2147483647;
} else {
/* no overflow, get the exact value */
e = i * (8 * SIZEOF_LIMB_T) + (e % (8 * SIZEOF_LIMB_T));
}
}
}
/* 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 (size < 0)
r = -r;
return r;
}
/* This only supports IEEE floating point */
void
integer_cbits_decodeDouble (MP_INT *man, 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 ) == SIZEOF_DOUBLE);
ASSERT(sizeof(man->_mp_d[0]) == SIZEOF_LIMB_T);
ASSERT(DNBIGIT*SIZEOF_LIMB_T >= SIZEOF_DOUBLE);
u.d = dbl; /* grab chunks of the double */
low = u.i[L];
high = u.i[H];
/* we know the MP_INT* passed in has size zero, so we realloc
no matter what.
*/
man->_mp_alloc = DNBIGIT;
if (low == 0 && (high & ~DMSBIT) == 0) {
man->_mp_size = 0;
*exp = 0L;
} else {
man->_mp_size = DNBIGIT;
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;
#if DNBIGIT == 2
man->_mp_d[0] = (mp_limb_t)low;
man->_mp_d[1] = (mp_limb_t)high;
#else
#if DNBIGIT == 1
man->_mp_d[0] = ((mp_limb_t)high) << 32 | (mp_limb_t)low;
#else
#error Cannot cope with DNBIGIT
#endif
#endif
if (sign < 0)
man->_mp_size = -man->_mp_size;
}
}