27  * Use is subject to license terms.
  28  */
  29 
  30 /*
  31  * arccosin function
  32  *                            ________
  33  *                           / 1 - x
  34  *      acos(x) = 2*atan2(  / -------- , 1 )
  35  *                        \/   1 + x
  36  *
  37  *                            ________
  38  *                           / 1 - x
  39  *              = 2*atan (  / -------- ) for non-exceptional x.
  40  *                        \/   1 + x
  41  *
  42  * Special cases:
  43  *      if x is NaN, return x itself;
  44  *      if |x|>1, return NaN with invalid signal.
  45  */
  46 
  47 #pragma weak acosl = __acosl
  48 
  49 #include "libm.h"
  50 
  51 static const long double zero = 0.0L, one = 1.0L;
  52 
  53 long double
  54 acosl(long double x) {
  55         if (isnanl(x))
  56                 return (x + x);
  57         else if (fabsl(x) < one)
  58                 x = atanl(sqrtl((one - x) / (one + x)));
  59         else if (x == -one)
  60                 x = atan2l(one, zero);  /* x <- PI */
  61         else if (x == one)
  62                 x = zero;
  63         else {          /* |x| > 1  create invalid signal */
  64                 return (zero / zero);
  65         }
  66         return (x + x);
  67 }

  27  * Use is subject to license terms.
  28  */
  29 
  30 /*
  31  * arccosin function
  32  *                            ________
  33  *                           / 1 - x
  34  *      acos(x) = 2*atan2(  / -------- , 1 )
  35  *                        \/   1 + x
  36  *
  37  *                            ________
  38  *                           / 1 - x
  39  *              = 2*atan (  / -------- ) for non-exceptional x.
  40  *                        \/   1 + x
  41  *
  42  * Special cases:
  43  *      if x is NaN, return x itself;
  44  *      if |x|>1, return NaN with invalid signal.
  45  */
  46 
  47 #pragma weak __acosl = acosl
  48 
  49 #include "libm.h"
  50 
  51 static const long double zero = 0.0L, one = 1.0L;
  52 
  53 long double
  54 acosl(long double x) {
  55         if (isnanl(x))
  56                 return (x + x);
  57         else if (fabsl(x) < one)
  58                 x = atanl(sqrtl((one - x) / (one + x)));
  59         else if (x == -one)
  60                 x = atan2l(one, zero);  /* x <- PI */
  61         else if (x == one)
  62                 x = zero;
  63         else {          /* |x| > 1  create invalid signal */
  64                 return (zero / zero);
  65         }
  66         return (x + x);
  67 }