lib/libc/gen/modf.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * modf(double x, double *iptr)
  14  * return fraction part of x, and return x's integral part in *iptr.
  15  * Method:
  16  *      Bit twiddling.
  17  *
  18  * Exception:
  19  *      No exception.
  20  */
  21
  22 #include <sys/types.h>
  23 #include <machine/endian.h>
  24 #include <math.h>
  25
  26 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
  27
  28 #if BYTE_ORDER == BIG_ENDIAN
  29
  30 typedef union
  31 {
  32   double value;
  33   struct
  34   {
  35     u_int32_t msw;
  36     u_int32_t lsw;
  37   } parts;
  38 } ieee_double_shape_type;
  39
  40 #endif
  41
  42 #if BYTE_ORDER == LITTLE_ENDIAN
  43
  44 typedef union
  45 {
  46   double value;
  47   struct
  48   {
  49     u_int32_t lsw;
  50     u_int32_t msw;
  51   } parts;
  52 } ieee_double_shape_type;
  53
  54 #endif
  55
  56 /* Get two 32 bit ints from a double.  */
  57
  58 #define EXTRACT_WORDS(ix0,ix1,d)                                \
  59 do {                                                            \
  60   ieee_double_shape_type ew_u;                                  \
  61   ew_u.value = (d);                                             \
  62   (ix0) = ew_u.parts.msw;                                       \
  63   (ix1) = ew_u.parts.lsw;                                       \
  64 } while (0)
  65
  66 /* Get the more significant 32 bit int from a double.  */
  67
  68 #define GET_HIGH_WORD(i,d)                                      \
  69 do {                                                            \
  70   ieee_double_shape_type gh_u;                                  \
  71   gh_u.value = (d);                                             \
  72   (i) = gh_u.parts.msw;                                         \
  73 } while (0)
  74
  75 /* Set a double from two 32 bit ints.  */
  76
  77 #define INSERT_WORDS(d,ix0,ix1)                                 \
  78 do {                                                            \
  79   ieee_double_shape_type iw_u;                                  \
  80   iw_u.parts.msw = (ix0);                                       \
  81   iw_u.parts.lsw = (ix1);                                       \
  82   (d) = iw_u.value;                                             \
  83 } while (0)
  84
  85 static const double one = 1.0;
  86
  87 double
  88 modf(double x, double *iptr)
  89 {
  90         int32_t i0,i1,j0;
  91         u_int32_t i;
  92         EXTRACT_WORDS(i0,i1,x);
  93         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  94         if(j0<20) {                     /* integer part in high x */
  95             if(j0<0) {                  /* |x|<1 */
  96                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
  97                 return x;
  98             } else {
  99                 i = (0x000fffff)>>j0;
 100                 if(((i0&i)|i1)==0) {            /* x is integral */
 101                     u_int32_t high;
 102                     *iptr = x;
 103                     GET_HIGH_WORD(high,x);
 104                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
 105                     return x;
 106                 } else {
 107                     INSERT_WORDS(*iptr,i0&(~i),0);
 108                     return x - *iptr;
 109                 }
 110             }
 111         } else if (j0>51) {             /* no fraction part */
 112             u_int32_t high;
 113             if (j0 == 0x400) {          /* inf/NaN */
 114                 *iptr = x;
 115                 return 0.0 / x;
 116             }
 117             *iptr = x*one;
 118             GET_HIGH_WORD(high,x);
 119             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
 120             return x;
 121         } else {                        /* fraction part in low x */
 122             i = ((u_int32_t)(0xffffffff))>>(j0-20);
 123             if((i1&i)==0) {             /* x is integral */
 124                 u_int32_t high;
 125                 *iptr = x;
 126                 GET_HIGH_WORD(high,x);
 127                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
 128                 return x;
 129             } else {
 130                 INSERT_WORDS(*iptr,i0,i1&(~i));
 131                 return x - *iptr;
 132             }
 133         }
 134 }