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#include "bid_trans.h"

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

BID_F128_CONST_DEF( c_1em40, 3f7a16c262777579, c58c46475896767b); // 1e-40
BID_F128_CONST_DEF( c_one,        3fff000000000000, 0000000000000000); // 1.0

BID128_FUNCTION_ARG1 (bid128_expm1, x)

// Declare local variables

  BID_UINT128 res, t;
  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);
   }

// Convert to binary

  BIDECIMAL_CALL1(bid128_to_binary128,xd,x);

// If the input is really small, the result is about x + x^2/2, which
// we do weakly just to make sure all the directed roundings are OK.
// Treat zero specially to copy its sign

  __bid_f128_fabs(abs_xd, xd); 
  if (__bid_f128_le(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,x,x);
      }                                               
     BID_RETURN(res);                              
     BID_RETURN(res);
   }

// Otherwise if the input is <= 1, the naive computation is well-conditioned
// and will neither overflow nor underflow

  else if (__bid_f128_le(xd, c_one.v))
   { __bid_f128_expm1(yd, xd);
     BIDECIMAL_CALL1(binary128_to_bid128,res,yd);
     BID_RETURN(res);
   }

// Otherwise it's not bad to just call exp and subtract 1. For
// moderate results, this will be exact, and for large results, it
// will be irrelevant. Even in the awkward middle ground where
// ulp(y) is about 2, it will be OK, just another ulp at most.

  else
   { BIDECIMAL_CALL1(bid128_exp,t,x);
     BIDECIMAL_CALL2(bid128_sub,res,t,BID128_1);
     BID_RETURN(res);
   }
}
