src/libm/s_scalbn.c
changeset 2756 a98604b691c8
child 3162 dc1eb82ffdaa
equal deleted inserted replaced
2755:2a3ec308d995 2756:a98604b691c8
       
     1 /* @(#)s_scalbn.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 #if defined(LIBM_SCCS) && !defined(lint)
       
    14 static char rcsid[] =
       
    15     "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
       
    16 #endif
       
    17 
       
    18 /*
       
    19  * scalbn (double x, int n)
       
    20  * scalbn(x,n) returns x* 2**n  computed by  exponent
       
    21  * manipulation rather than by actually performing an
       
    22  * exponentiation or a multiplication.
       
    23  */
       
    24 
       
    25 #include "math.h"
       
    26 #include "math_private.h"
       
    27 
       
    28 libm_hidden_proto(copysign)
       
    29 #ifdef __STDC__
       
    30      static const double
       
    31 #else
       
    32      static double
       
    33 #endif
       
    34        two54 = 1.80143985094819840000e+16,      /* 0x43500000, 0x00000000 */
       
    35          twom54 = 5.55111512312578270212e-17,   /* 0x3C900000, 0x00000000 */
       
    36          huge = 1.0e+300, tiny = 1.0e-300;
       
    37 
       
    38 libm_hidden_proto(scalbn)
       
    39 #ifdef __STDC__
       
    40      double scalbn(double x, int n)
       
    41 #else
       
    42      double scalbn(x, n)
       
    43      double x;
       
    44      int n;
       
    45 #endif
       
    46 {
       
    47     int32_t k, hx, lx;
       
    48     EXTRACT_WORDS(hx, lx, x);
       
    49     k = (hx & 0x7ff00000) >> 20;        /* extract exponent */
       
    50     if (k == 0) {               /* 0 or subnormal x */
       
    51         if ((lx | (hx & 0x7fffffff)) == 0)
       
    52             return x;           /* +-0 */
       
    53         x *= two54;
       
    54         GET_HIGH_WORD(hx, x);
       
    55         k = ((hx & 0x7ff00000) >> 20) - 54;
       
    56         if (n < -50000)
       
    57             return tiny * x;    /*underflow */
       
    58     }
       
    59     if (k == 0x7ff)
       
    60         return x + x;           /* NaN or Inf */
       
    61     k = k + n;
       
    62     if (k > 0x7fe)
       
    63         return huge * copysign(huge, x);        /* overflow  */
       
    64     if (k > 0) {                /* normal result */
       
    65         SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    66         return x;
       
    67     }
       
    68     if (k <= -54) {
       
    69         if (n > 50000)          /* in case integer overflow in n+k */
       
    70             return huge * copysign(huge, x);    /*overflow */
       
    71         else
       
    72             return tiny * copysign(tiny, x);    /*underflow */
       
    73     }
       
    74     k += 54;                    /* subnormal result */
       
    75     SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    76     return x * twom54;
       
    77 }
       
    78 
       
    79 libm_hidden_def(scalbn)