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#include "bid_trans.h"

// -1, used in sqrt(1 - x^2) computation

static BID_UINT128 BID128_MINUS1 =
  {BID128_LH_INIT( 0x0000000000000001ull, 0xb040000000000000ull )};

// 10^-40, used in trivial path

static BID_UINT128 BID128_10PM40 =
  {BID128_LH_INIT( 0x0000000000000001ull, 0x2ff0000000000000ull )};

// NaN for inputs |x| > 1                                                   
                                                                          
static BID_UINT128 BID128_NAN =                                          
  {BID128_LH_INIT( 0x0000000000000000ull, 0x7c00000000000000ull )};                   

BID_F128_CONST_DEF( c_1em40, 3f7a16c262777579, c58c46475896767b); // 1e-40
BID_F128_CONST_DEF( c_7_10ths, 3ffe666666666666, 6666666666666666); // .7
BID_F128_CONST_DEF( c_one,     3fff000000000000, 0000000000000000); // 1.0
BID_F128_CONST_DEF( c_zero,    0000000000000000, 0000000000000000); // 0.0

BID128_FUNCTION_ARG1 (bid128_asin, x)

// Declare local variables

  BID_UINT128 res, t;
  BID_F128_TYPE xd, td, yd, abs_xd;
  BID_UINT128 tm1 = BID128_MINUS1;
  BID_UINT128 t10pm40 = BID128_10PM40;

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

  if ((x.w[BID_HIGH_128W] & NAN_MASK64) == NAN_MASK64)
   {
     #ifdef BID_SET_STATUS_FLAGS
     if (((x.w[BID_HIGH_128W] & SNAN_MASK64) == SNAN_MASK64))
        __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);
     #endif
     res.w[BID_HIGH_128W] = x.w[BID_HIGH_128W] & 0xfc003fffffffffffull;
     res.w[BID_LOW_128W] = x.w[BID_LOW_128W];
     if (((res.w[BID_HIGH_128W] & 0x00003fffffffffffull) >
          0x0000314dc6448d93ull) ||
         (((res.w[BID_HIGH_128W] & 0x00003fffffffffffull) ==
            0x0000314dc6448d93ull) &&
          res.w[BID_LOW_128W] >= 0x38c15b0a00000000ull))
      { res.w[BID_HIGH_128W] &= ~0x00003fffffffffffull;
        res.w[BID_LOW_128W] = 0ull;
      }
     BID_RETURN(res);
   }

// Convert to binary

  BIDECIMAL_CALL1(bid128_to_binary128,xd,x);

// If the input is very small indeed, do a special computation, since
// the conversion to binary may already have underflowed to zero.
// The computation is just x * (1 + e), to work with directed rounding.

  __bid_f128_fabs(abs_xd, xd);
  if (__bid_f128_lt(abs_xd, c_1em40.v))
   { BIDECIMAL_CALL3(bid128_fma,res,x,t10pm40,x);
     BID_RETURN(res);
   }

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

  if (__bid_f128_le(abs_xd, c_7_10ths.v))
   { __bid_f128_asin(yd, xd);
     BIDECIMAL_CALL1(binary128_to_bid128,res,yd);
     BID_RETURN (res);
   }

// If the input is > 1 in magnitude, fail                      
                                                                             
  else if (__bid_f128_gt(abs_xd, c_one.v))                                             
   { res = BID128_NAN;                                                      
     #ifdef BID_SET_STATUS_FLAGS                                              
     __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);                  
     #endif                                                           
     BID_RETURN(res)                                                      
   }                                                              

// Otherwise compute sqrt(1 - x^2) accurately and use acos instead.

  else
   { BIDECIMAL_CALL3(bid128_fma,t,x,x,tm1);
     BIDECIMAL_CALL1(bid128_to_binary128,td,t);
     __bid_f128_neg(yd, td); 
     __bid_f128_sqrt(yd, yd);
     __bid_f128_acos(yd, yd);
     if (__bid_f128_lt(xd, c_zero.v)) __bid_f128_neg(yd, yd);
     BIDECIMAL_CALL1(binary128_to_bid128,res,yd);
     BID_RETURN (res);
   }
}
