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#include "bid_trans.h"

#define BID64_1 0x31c0000000000001ull

BID_F80_CONST_DEF( c_9_10ths, 3ffecccccccccccc, cccccccccccccccd); // .9
BID_F80_CONST_DEF( c_pi,      4000921fb54442d1, 8469898cc51701b8); // pi 
BID_F80_CONST_DEF( c_zero,    0000000000000000, 0000000000000000); // 0.0
BID_F80_CONST_DEF( c_one,     3fff000000000000, 0000000000000000); // 1.0
BID_F80_CONST_DEF( c_two,     4000000000000000, 0000000000000000); // 2.0

// Canonical zero with minimal exponent

#define BID64_0 0x0000000000000000ull

// NaN for values |x| > 1

#define BID64_NAN 0x7c00000000000000ull

BID_TYPE0_FUNCTION_ARGTYPE1(BID_UINT64, bid64_acos, BID_UINT64, x)

// Declare local variables

  BID_UINT64 res, t, t1 = BID64_1;
  BID_F80_TYPE xd, td, yd, abs_xd, rt;

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

  if ((x & NAN_MASK64) == NAN_MASK64)
   {
     #ifdef BID_SET_STATUS_FLAGS
     if ((x & SNAN_MASK64) == SNAN_MASK64)
        __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);
     #endif
     res = x & 0xfc03ffffffffffffull;
     if ((res & 0x0003ffffffffffffull) > 999999999999999ull)
        res &= ~0x0003ffffffffffffull;
     BID_RETURN(res);
   }

// Convert to binary

  BIDECIMAL_CALL1(bid64_to_binary80,xd,x);

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


  __bid_f80_fabs(abs_xd, xd);
  if (__bid_f80_le(abs_xd, c_9_10ths.v))
   {
      __bid_f80_acos(yd, xd);
     BIDECIMAL_CALL1(binary80_to_bid64,res,yd);
     BID_RETURN (res);
   }

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

  else if (__bid_f80_gt(abs_xd, c_one.v) )
   {
     res = BID64_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 (__bid_f80_ge(xd, c_one.v))
   {
     res = BID64_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(bid64_abs,t,x);
     BIDECIMAL_CALL2(bid64_sub,t,t1,t);
     BIDECIMAL_CALL1(bid64_to_binary80,td,t);
     __bid_f80_sub(rt, c_two.v, td);
     __bid_f80_mul(td, rt, td);
     __bid_f80_sqrt(yd, td);
     __bid_f80_asin(yd, yd);
     if ( __bid_f80_lt(xd, c_zero.v) ) __bid_f80_sub(yd, c_pi.v, yd );
     BIDECIMAL_CALL1(binary80_to_bid64,res,yd);
     BID_RETURN (res);
   }
}
