libm/s_scalbn.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  * scalbln(double x, long n)
  14  * scalbln(x,n) returns x * 2**n computed by exponent
  15  * manipulation rather than by actually performing an
  16  * exponentiation or a multiplication.
  17  */
  18
  19 #include "math.h"
  20 #include "math_private.h"
  21 #include <limits.h>
  22
  23 static const double
  24 two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
  25 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
  26 huge   = 1.0e+300,
  27 tiny   = 1.0e-300;
  28
  29 double scalbln(double x, long n)
  30 {
  31         int32_t k, hx, lx;
  32
  33         EXTRACT_WORDS(hx, lx, x);
  34         k = (hx & 0x7ff00000) >> 20; /* extract exponent */
  35         if (k == 0) { /* 0 or subnormal x */
  36                 if ((lx | (hx & 0x7fffffff)) == 0)
  37                         return x; /* +-0 */
  38                 x *= two54;
  39                 GET_HIGH_WORD(hx, x);
  40                 k = ((hx & 0x7ff00000) >> 20) - 54;
  41         }
  42         if (k == 0x7ff)
  43                 return x + x; /* NaN or Inf */
  44         k = k + n;
  45         if (k > 0x7fe)
  46                 return huge * copysign(huge, x); /* overflow */
  47         if (n < -50000)
  48                 return tiny * copysign(tiny, x); /* underflow */
  49         if (k > 0) { /* normal result */
  50                 SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
  51                 return x;
  52         }
  53         if (k <= -54) {
  54                 if (n > 50000) /* in case integer overflow in n+k */
  55                         return huge * copysign(huge, x); /* overflow */
  56                 return tiny * copysign(tiny, x); /* underflow */
  57         }
  58         k += 54; /* subnormal result */
  59         SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
  60         return x * twom54;
  61 }
  62 libm_hidden_def(scalbln)
  63
  64 #if LONG_MAX == INT_MAX
  65 strong_alias_untyped(scalbln,scalbn)
  66 #else
  67 double scalbn(double x, int n)
  68 {
  69         return scalbln(x, n);
  70 }
  71 #endif
  72 libm_hidden_def(scalbn)