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