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#include "bid_internal.h"
double acos(double);
double asin(double);
double fabs(double);
double sqrt(double);

#define BID32_1         0x32800001ul
#define BID32_0         0x00000000ul

// NaN for inputs |x| > 1

#define BID32_NAN 0x7c000000ul

BID_TYPE0_FUNCTION_ARGTYPE1(BID_UINT32, bid32_acos, BID_UINT32, x)


// Declare local variables

  BID_UINT32 res, t, t1 = BID32_1;
  double xd, td, yd;

// Check for NaN and just return the same NaN, quieted and canonized

  if ((x & NAN_MASK32) == NAN_MASK32)
   {
     #ifdef BID_SET_STATUS_FLAGS
     if ((x & SNAN_MASK32) == SNAN_MASK32)
        __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);
     #endif
     res = x & 0xfc0ffffful;
     if ((res & 0x000ffffful) > 999999ul) res &= ~0x000ffffful;
     BID_RETURN(res);
   }

// Convert to binary

  BIDECIMAL_CALL1(bid32_to_binary64,xd,x);

// If the input is not too close to +/- 1 then do it "naively"

  if (fabs(xd) <= 0.9)
   { yd = acos(xd);
     BIDECIMAL_CALL1(binary64_to_bid32,res,yd);
     BID_RETURN (res);
   }

// If the input is > 1 in magnitude, fail

  else if (fabs(xd) > 1.0)
   { res = BID32_NAN;
     #ifdef BID_SET_STATUS_FLAGS
     __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);
     #endif
     BID_RETURN(res)
   }

// If the input is exactly 1, return a canonical zero with minimal exponent
// Uses >= 1 instead of == 1 to avoid compiler warnings...

  else if (xd >= 1.0)
   { res = BID32_0;
     BID_RETURN(res);
   }

// Otherwise compute sqrt(1 - x^2) accurately and use asin instead.
// Use 1 - |x| as direct decimal computation, since direct fma would
// give only about working precision error near +1

  else
   { BIDECIMAL_CALL1_NORND_NOSTAT(bid32_abs,t,x);
     BIDECIMAL_CALL2(bid32_sub,t,t1,t);
     BIDECIMAL_CALL1(bid32_to_binary64,td,t);
     td = (2.0 - td) * td;
     yd = asin(sqrt(td));
     if (xd < 0.0) yd = 3.1415926535897932384626433832795028842 - yd;
     BIDECIMAL_CALL1(binary64_to_bid32,res,yd);
     BID_RETURN (res);
   }
}
