rts/StgPrimFloat.c

   1 /* -----------------------------------------------------------------------------
   2  *
   3  * (c) Lennart Augustsson
   4  * (c) The GHC Team, 1998-2000
   5  *
   6  * Miscellaneous support for floating-point primitives
   7  *
   8  * ---------------------------------------------------------------------------*/
   9
  10 #include "PosixSource.h"
  11 #include "Rts.h"
  12
  13 #include "StgPrimFloat.h"
  14
  15 #include <math.h>
  16 #include <float.h>
  17
  18 #define IEEE_FLOATING_POINT 1
  19
  20 #if FLT_RADIX != 2
  21 # error FLT_RADIX != 2 not supported
  22 #endif
  23
  24 /*
  25  * Encoding and decoding Doubles.  Code based on the HBC code
  26  * (lib/fltcode.c).
  27  */
  28
  29 #if IEEE_FLOATING_POINT
  30 #define MY_DMINEXP  ((DBL_MIN_EXP) - (DBL_MANT_DIG) - 1)
  31 /* DMINEXP is defined in values.h on Linux (for example) */
  32 #define DHIGHBIT 0x00100000
  33 #define DMSBIT   0x80000000
  34
  35 #define MY_FMINEXP  ((FLT_MIN_EXP) - (FLT_MANT_DIG) - 1)
  36 #define FHIGHBIT 0x00800000
  37 #define FMSBIT   0x80000000
  38 #endif
  39
  40 #if defined(WORDS_BIGENDIAN) || defined(FLOAT_WORDS_BIGENDIAN)
  41 #define L 1
  42 #define H 0
  43 #else
  44 #define L 0
  45 #define H 1
  46 #endif
  47
  48 #define __abs(a)                (( (a) >= 0 ) ? (a) : (-(a)))
  49
  50 /* Special version for words */
  51 StgDouble
  52 __word_encodeDouble (W_ j, I_ e)
  53 {
  54   StgDouble r;
  55
  56   r = (StgDouble)j;
  57
  58   /* Now raise to the exponent */
  59   if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
  60     r = ldexp(r, e);
  61
  62   return r;
  63 }
  64
  65 /* Special version for small Integers */
  66 StgDouble
  67 __int_encodeDouble (I_ j, I_ e)
  68 {
  69   StgDouble r;
  70
  71   r = (StgDouble)__abs(j);
  72
  73   /* Now raise to the exponent */
  74   if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
  75     r = ldexp(r, e);
  76
  77   /* sign is encoded in the size */
  78   if (j < 0)
  79     r = -r;
  80
  81   return r;
  82 }
  83
  84 /* Special version for small Integers */
  85 StgFloat
  86 __int_encodeFloat (I_ j, I_ e)
  87 {
  88   StgFloat r;
  89
  90   r = (StgFloat)__abs(j);
  91
  92   /* Now raise to the exponent */
  93   if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
  94     r = ldexp(r, e);
  95
  96   /* sign is encoded in the size */
  97   if (j < 0)
  98     r = -r;
  99
 100   return r;
 101 }
 102
 103 /* Special version for small positive Integers */
 104 StgFloat
 105 __word_encodeFloat (W_ j, I_ e)
 106 {
 107   StgFloat r;
 108
 109   r = (StgFloat)j;
 110
 111   /* Now raise to the exponent */
 112   if ( r != 0.0 ) /* Lennart suggests this avoids a bug in MIPS's ldexp */
 113     r = ldexp(r, e);
 114
 115   return r;
 116 }
 117
 118 /* This only supports IEEE floating point */
 119
 120 void
 121 __decodeDouble_2Int (I_ *man_sign, W_ *man_high, W_ *man_low, I_ *exp, StgDouble dbl)
 122 {
 123     /* Do some bit fiddling on IEEE */
 124     unsigned int low, high;             /* assuming 32 bit ints */
 125     int sign, iexp;
 126     union { double d; unsigned int i[2]; } u;   /* assuming 32 bit ints, 64 bit double */
 127
 128     ASSERT(sizeof(unsigned int ) == 4            );
 129     ASSERT(sizeof(dbl          ) == 8            );
 130     ASSERT(sizeof(dbl          ) == SIZEOF_DOUBLE);
 131
 132     u.d = dbl;      /* grab chunks of the double */
 133     low = u.i[L];
 134     high = u.i[H];
 135
 136     if (low == 0 && (high & ~DMSBIT) == 0) {
 137         *man_low = 0;
 138         *man_high = 0;
 139         *exp = 0L;
 140     } else {
 141         iexp = ((high >> 20) & 0x7ff) + MY_DMINEXP;
 142         sign = high;
 143
 144         high &= DHIGHBIT-1;
 145         if (iexp != MY_DMINEXP) /* don't add hidden bit to denorms */
 146             high |= DHIGHBIT;
 147         else {
 148             iexp++;
 149             /* A denorm, normalize the mantissa */
 150             while (! (high & DHIGHBIT)) {
 151                 high <<= 1;
 152                 if (low & DMSBIT)
 153                     high++;
 154                 low <<= 1;
 155                 iexp--;
 156             }
 157         }
 158         *exp = (I_) iexp;
 159         *man_low = low;
 160         *man_high = high;
 161         *man_sign = (sign < 0) ? -1 : 1;
 162     }
 163 }
 164
 165 /* This is expected to replace uses of __decodeDouble_2Int() in the long run */
 166 StgInt
 167 __decodeDouble_Int64 (StgInt64 *const mantissa, const StgDouble dbl)
 168 {
 169 #if 0
 170     // We can't use this yet as-is, see ticket #9810
 171     if (dbl) {
 172         int exp = 0;
 173         *mantissa = (StgInt64)scalbn(frexp(dbl, &exp), DBL_MANT_DIG);
 174         return exp-DBL_MANT_DIG;
 175     } else {
 176         *mantissa = 0;
 177         return 0;
 178     }
 179 #else
 180     I_ man_sign = 0;
 181     W_ man_high = 0, man_low = 0;
 182     I_ exp = 0;
 183
 184     __decodeDouble_2Int (&man_sign, &man_high, &man_low, &exp, dbl);
 185     ASSIGN_Int64((W_*)mantissa, ((((StgInt64)man_high << 32)
 186                                   | (StgInt64)man_low)
 187                                  * (StgInt64)man_sign));
 188     return exp;
 189 #endif
 190 }
 191
 192 /* Convenient union types for checking the layout of IEEE 754 types -
 193    based on defs in GNU libc <ieee754.h>
 194 */
 195
 196 void
 197 __decodeFloat_Int (I_ *man, I_ *exp, StgFloat flt)
 198 {
 199     /* Do some bit fiddling on IEEE */
 200     int high, sign;                 /* assuming 32 bit ints */
 201     union { float f; int i; } u;    /* assuming 32 bit float and int */
 202
 203     ASSERT(sizeof(int          ) == 4            );
 204     ASSERT(sizeof(flt          ) == 4            );
 205     ASSERT(sizeof(flt          ) == SIZEOF_FLOAT );
 206
 207     u.f = flt;      /* grab the float */
 208     high = u.i;
 209
 210     if ((high & ~FMSBIT) == 0) {
 211         *man = 0;
 212         *exp = 0;
 213     } else {
 214         *exp = ((high >> 23) & 0xff) + MY_FMINEXP;
 215         sign = high;
 216
 217         high &= FHIGHBIT-1;
 218         if (*exp != MY_FMINEXP) /* don't add hidden bit to denorms */
 219             high |= FHIGHBIT;
 220         else {
 221             (*exp)++;
 222             /* A denorm, normalize the mantissa */
 223             while (! (high & FHIGHBIT)) {
 224                 high <<= 1;
 225                 (*exp)--;
 226             }
 227         }
 228         *man = high;
 229         if (sign < 0)
 230             *man = - *man;
 231     }
 232 }
 233