lib/libc/gen/modf.c

   1 /* @(#)s_modf.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #include <sys/cdefs.h>
  14 __FBSDID("$FreeBSD$");
  15
  16 /*
  17  * modf(double x, double *iptr)
  18  * return fraction part of x, and return x's integral part in *iptr.
  19  * Method:
  20  *      Bit twiddling.
  21  *
  22  * Exception:
  23  *      No exception.
  24  */
  25
  26 #include <sys/types.h>
  27 #include <machine/endian.h>
  28 #include <math.h>
  29
  30 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
  31
  32 #if BYTE_ORDER == BIG_ENDIAN
  33
  34 typedef union
  35 {
  36   double value;
  37   struct
  38   {
  39     u_int32_t msw;
  40     u_int32_t lsw;
  41   } parts;
  42 } ieee_double_shape_type;
  43
  44 #endif
  45
  46 #if BYTE_ORDER == LITTLE_ENDIAN
  47
  48 typedef union
  49 {
  50   double value;
  51   struct
  52   {
  53     u_int32_t lsw;
  54     u_int32_t msw;
  55   } parts;
  56 } ieee_double_shape_type;
  57
  58 #endif
  59
  60 /* Get two 32 bit ints from a double.  */
  61
  62 #define EXTRACT_WORDS(ix0,ix1,d)                                \
  63 do {                                                            \
  64   ieee_double_shape_type ew_u;                                  \
  65   ew_u.value = (d);                                             \
  66   (ix0) = ew_u.parts.msw;                                       \
  67   (ix1) = ew_u.parts.lsw;                                       \
  68 } while (0)
  69
  70 /* Get the more significant 32 bit int from a double.  */
  71
  72 #define GET_HIGH_WORD(i,d)                                      \
  73 do {                                                            \
  74   ieee_double_shape_type gh_u;                                  \
  75   gh_u.value = (d);                                             \
  76   (i) = gh_u.parts.msw;                                         \
  77 } while (0)
  78
  79 /* Set a double from two 32 bit ints.  */
  80
  81 #define INSERT_WORDS(d,ix0,ix1)                                 \
  82 do {                                                            \
  83   ieee_double_shape_type iw_u;                                  \
  84   iw_u.parts.msw = (ix0);                                       \
  85   iw_u.parts.lsw = (ix1);                                       \
  86   (d) = iw_u.value;                                             \
  87 } while (0)
  88
  89 static const double one = 1.0;
  90
  91 double
  92 modf(double x, double *iptr)
  93 {
  94         int32_t i0,i1,j0;
  95         u_int32_t i;
  96         EXTRACT_WORDS(i0,i1,x);
  97         j0 = ((i0>>20)&0x7ff)-0x3ff;    /* exponent of x */
  98         if(j0<20) {                     /* integer part in high x */
  99             if(j0<0) {                  /* |x|<1 */
 100                 INSERT_WORDS(*iptr,i0&0x80000000,0);    /* *iptr = +-0 */
 101                 return x;
 102             } else {
 103                 i = (0x000fffff)>>j0;
 104                 if(((i0&i)|i1)==0) {            /* x is integral */
 105                     u_int32_t high;
 106                     *iptr = x;
 107                     GET_HIGH_WORD(high,x);
 108                     INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
 109                     return x;
 110                 } else {
 111                     INSERT_WORDS(*iptr,i0&(~i),0);
 112                     return x - *iptr;
 113                 }
 114             }
 115         } else if (j0>51) {             /* no fraction part */
 116             u_int32_t high;
 117             if (j0 == 0x400) {          /* inf/NaN */
 118                 *iptr = x;
 119                 return 0.0 / x;
 120             }
 121             *iptr = x*one;
 122             GET_HIGH_WORD(high,x);
 123             INSERT_WORDS(x,high&0x80000000,0);  /* return +-0 */
 124             return x;
 125         } else {                        /* fraction part in low x */
 126             i = ((u_int32_t)(0xffffffff))>>(j0-20);
 127             if((i1&i)==0) {             /* x is integral */
 128                 u_int32_t high;
 129                 *iptr = x;
 130                 GET_HIGH_WORD(high,x);
 131                 INSERT_WORDS(x,high&0x80000000,0);      /* return +-0 */
 132                 return x;
 133             } else {
 134                 INSERT_WORDS(*iptr,i0,i1&(~i));
 135                 return x - *iptr;
 136             }
 137         }
 138 }