mingw-w64-crt/math/powi.def.h

/*
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*/

/* IEEE 754 - Elementary Functions - Special Cases
 * powi (x, +/-0) is 1 for any x (even a zero, quiet NaN, or infinity)
 * powi (+1, y) is 1 for any y (even a quiet NaN)
 * powi (+/-0, y) is +/-oo and signals the divideByZero exception for y an odd integer < 0
 * powi (+/-0, y) is +oo and signals the divideByZero exception for finite y < 0 and not an odd integer
 * powi (+/-0, y) is +/-0 for finite y > 0 an odd integer
 * powi (+/-0, y) is +0 for finite y > 0 and not an odd integer
 powi (-inf, y) = +0 for y<0 and not an odd integer
 powi (-inf, y) = -inf for y an odd integer > 0
 powi (-inf, y) = +inf for y>0 and not an odd integer
 powi (+/-inf, y) is +/-0 with no exception for y an odd integer < 0
 powi (+/-inf, y) is +0 with no exception for finite y < 0 and not an odd integer
 powi (+/-inf, y) is +/-inf with no exception for finite y > 0 an odd integer
 powi (+/-inf, y) is +inf with no exception for finite y > 0 and not an odd integer
 powi (x, y) signals the invalid operation exception for finite x < 0 and finite non-integer y.
 
 For x /= 0: lim y->oo (1/x)^y results as: for |x| < 1 that sgn(x)*0 and for |x| > 0 that sgn(x)*Infinity

*/
#include "../complex/complex_internal.h"
#include <errno.h>
#include <limits.h>
#include <fenv.h>
#include <math.h>
#include <errno.h>

__FLT_TYPE __cdecl
__FLT_ABI(__powi) (__FLT_TYPE x, int y);

__FLT_TYPE __cdecl
__FLT_ABI(__powi) (__FLT_TYPE x, int y)
{
  int x_class = fpclassify (x);
  int odd_y = y & 1;
  __FLT_TYPE d, rslt;

  if (y == 0 || x == __FLT_CST(1.0))
    return __FLT_CST(1.0);
  else if (x_class == FP_NAN)
    {
      rslt = (signbit(x) ? -__FLT_NAN : __FLT_NAN);
      __FLT_RPT_DOMAIN ("__powi", x, (__FLT_TYPE) y, rslt);
      return rslt;
    }
  else if (x_class == FP_ZERO)
    {
      if (y >= 0)
	{
	  if (!odd_y || !signbit (x))
	    return __FLT_CST (0.0);
	  return -__FLT_CST(0.0);
	}

      if (!odd_y || !signbit (x))
	return __FLT_HUGE_VAL;
      return (signbit(x) ? -__FLT_HUGE_VAL : __FLT_HUGE_VAL);
    }
  else if (x_class == FP_INFINITE)
    {
      /* pow( -inf, y) = +0 for y<0 and not an odd integer,  */
      if (signbit(x) && y < 0 && !odd_y)
	return __FLT_CST(0.0);
      /* pow( -inf, y) = -inf for y an odd integer > 0.  */
      if (signbit(x) && y >= 0 && odd_y)
	return -__FLT_HUGE_VAL;
      /* pow( -inf, y) = +inf for y>0 and not an odd integer.  */
      if (signbit(x) && y >= 0 && !odd_y)
	return __FLT_HUGE_VAL;
      /* pow (+/-inf, y) is +/-0 with no exception for y an odd integer < 0. */
      if (y < 0)
      {
        /* pow (+/-inf, y) is +0 with no exception for finite y < 0 and not an odd integer.  */
	return (odd_y && signbit(x) ? -__FLT_CST(0.0) : __FLT_CST(0.0));
      }
      /* pow (+/-inf, y) is +/-inf with no exception for finite y > 0 an odd integer.  */
      /* pow (+/-inf, y) is +inf with no exception for finite y > 0 and not an odd integer.  */
      return (odd_y && signbit(x) ? -__FLT_HUGE_VAL : __FLT_HUGE_VAL);
    }

  d = __FLT_ABI(fabs) (x);

  if (y < 0)
    {
      d = __FLT_CST(1.0) / d;
      y = -y;
    }

  if (!y)
    rslt = __FLT_CST(1.0);
  else if (y == 1)
    rslt = d;
  else
    {
      unsigned int u = (unsigned int) y;
      rslt = ((u & 1) != 0) ? d : __FLT_CST(1.0);
      u >>= 1;
      do
	{
	  d *= d;
	  if ((u & 1) != 0)
	    rslt *= d;
	  u >>= 1;
	}
      while (u > 0);
    }
  if (signbit (x) && odd_y)
    rslt = -rslt;
  return rslt;
}