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#include "bid_trans.h"

// -10^-40, used in trivial path

static BID_UINT128 BID128_10PM40 =
  {{ 0x0000000000000001ull, 0xaff0000000000000ull }};

// 1 for dummy canonizing operation

static BID_UINT128 BID128_1 = 
  {{ 0x0000000000000001ull, 0x3040000000000000ull }};

BID_F128_CONST_DEF( c_1em40, 3f7a16c262777579, c58c46475896767b); // 1e-40

BID128_FUNCTION_ARG1 (bid128_atan, x)

// Declare local variables

  BID_UINT128 res;
  BID_F128_TYPE xd, yd, abs_xd;

// 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);
   }

// Otherwise just do the operation "naively".
//
// However, we need to handle the case of very small inputs, which can
// underflow to zero in quad and incorrectly return zero instead of the
// argument. Trap this after conversion and do a crude operation to get
// appropriate directed rounding. Deal with zero specially to copy sign.
//
// Note that for very large decimal128 inputs, the result of conversion
// will be infinity. However, since the binary atan function will return
// the right answer of pi/2 [zero] in such cases, it hardly seems worth putting
// in a special-case check, which will rarely be needed and slows down the
// usual cases.

  BIDECIMAL_CALL1(bid128_to_binary128,xd,x);

  __bid_f128_fabs(abs_xd, xd);
  if (__bid_f128_lt(abs_xd, c_1em40.v))
   { int zf;
     BIDECIMAL_CALL1_NORND_NOSTAT(bid128_isZero,zf,x);
     if (zf)
      { BIDECIMAL_CALL2(bid128_mul,res,x,BID128_1);
      }
     else
      { BIDECIMAL_CALL3(bid128_fma,res,x,BID128_10PM40,x);
      }
     BID_RETURN(res);
   }
  else
   { __bid_f128_atan(yd, xd);
     BIDECIMAL_CALL1(binary128_to_bid128,res,yd);
     BID_RETURN(res);
   }
}
