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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.18.0/] [newlib/] [libm/] [mathfp/] [s_pow.c] - Blame information for rev 262

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1 207 jeremybenn
 
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/* @(#)z_pow.c 1.0 98/08/13 */
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/*
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FUNCTION
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        <<pow>>, <<powf>>---x to the power y
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INDEX
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        pow
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INDEX
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        powf
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ANSI_SYNOPSIS
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        #include <math.h>
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        double pow(double <[x]>, double <[y]>);
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        float pow(float <[x]>, float <[y]>);
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TRAD_SYNOPSIS
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        #include <math.h>
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        double pow(<[x]>, <[y]>);
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        double <[x]>, <[y]>;
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        float pow(<[x]>, <[y]>);
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        float <[x]>, <[y]>;
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DESCRIPTION
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        <<pow>> and <<powf>> calculate <[x]> raised to the exponent <[y]>.
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        @tex
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        (That is, $x^y$.)
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        @end tex
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RETURNS
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        On success, <<pow>> and <<powf>> return the value calculated.
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        When the argument values would produce overflow, <<pow>>
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        returns <<HUGE_VAL>> and set <<errno>> to <<ERANGE>>.  If the
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        argument <[x]> passed to <<pow>> or <<powf>> is a negative
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        noninteger, and <[y]> is also not an integer, then <<errno>>
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        is set to <<EDOM>>.  If <[x]> and <[y]> are both 0, then
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        <<pow>> and <<powf>> return <<1>>.
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        You can modify error handling for these functions using <<matherr>>.
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PORTABILITY
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        <<pow>> is ANSI C. <<powf>> is an extension.  */
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#include <float.h>
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#include "fdlibm.h"
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#include "zmath.h"
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#ifndef _DOUBLE_IS_32BITS
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double pow (double x, double y)
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{
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  double d, k, t, r = 1.0;
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  int n, sign, exponent_is_even_int = 0;
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  __uint32_t px;
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  GET_HIGH_WORD (px, x);
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  k = modf (y, &d);
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  if (k == 0.0)
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    {
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      /* Exponent y is an integer. */
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      if (modf (ldexp (y, -1), &t))
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        {
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          /* y is odd. */
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          exponent_is_even_int = 0;
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        }
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      else
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        {
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          /* y is even. */
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          exponent_is_even_int = 1;
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        }
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    }
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  if (x == 0.0)
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    {
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      if (y <= 0.0)
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        errno = EDOM;
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    }
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  else if ((t = y * log (fabs (x))) >= BIGX)
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    {
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      errno = ERANGE;
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      if (px & 0x80000000)
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        {
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          /* x is negative. */
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          if (k)
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            {
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              /* y is not an integer. */
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              errno = EDOM;
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              x = 0.0;
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            }
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          else if (exponent_is_even_int)
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            x = z_infinity.d;
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          else
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            x = -z_infinity.d;
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        }
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      else
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        {
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          x = z_infinity.d;
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        }
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    }
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  else if (t < SMALLX)
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    {
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      errno = ERANGE;
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      x = 0.0;
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    }
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  else
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    {
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      if ( !k && fabs(d) <= 32767 )
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        {
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          n = (int) d;
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          if ((sign = (n < 0)))
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            n = -n;
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          while ( n > 0 )
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            {
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              if ((unsigned int) n % 2)
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                r *= x;
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              x *= x;
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              n = (unsigned int) n / 2;
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            }
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          if (sign)
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            r = 1.0 / r;
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          return r;
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        }
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      else
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        {
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          if ( px & 0x80000000 )
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            {
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              /* x is negative. */
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              if ( k )
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                {
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                  /* y is not an integer. */
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                  errno = EDOM;
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                  return 0.0;
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                }
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            }
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          x = exp (t);
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          if (!exponent_is_even_int)
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            {
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              if (px & 0x80000000)
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                {
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                  /* y is an odd integer, and x is negative,
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                     so the result is negative. */
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                  GET_HIGH_WORD (px, x);
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                  px |= 0x80000000;
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                  SET_HIGH_WORD (x, px);
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                }
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            }
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        }
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    }
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  return x;
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}
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#endif _DOUBLE_IS_32BITS

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