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#include "bid_trans.h"

#define BID64_NAN 0x7c00000000000000ull

#define BID64_1 0x31c0000000000001ull

BID_F80_CONST_DEF( c_one,       3fff000000000000, 0000000000000000); // 1.0
BID_F80_CONST_DEF( c_half,      3ffe000000000000, 0000000000000000); // 0.5
BID_F80_CONST_DEF( c_1_ov_ln_2, 3fff71547652b82f, e1777d0ffda0d23a); // 1/ln(2)

BID_TYPE0_FUNCTION_ARGTYPE1(BID_UINT64, bid64_log2, BID_UINT64, x)

// Declare local variables

  BID_UINT64 res;
  BID_F80_TYPE xd, rd, e_bin, abs_e_bin;
  int z;

// 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);
   }

  BIDECIMAL_CALL1_NORND_NOSTAT (bid64_isZero, z, x);
  if (z)
   { // -Infinite and Divide by Zero according C99
     res = 0xf800000000000000ull;
     #ifdef BID_SET_STATUS_FLAGS
     __set_status_flags (pfpsf, BID_ZERO_DIVIDE_EXCEPTION);
     #endif
     BID_RETURN (res);
   }

  if (x & MASK_SIGN)
   { // QNaN Indefinite
     res = 0x7c00000000000000ull;
     #ifdef BID_SET_STATUS_FLAGS
     __set_status_flags (pfpsf, BID_INVALID_EXCEPTION);
     #endif
     BID_RETURN (res);
   }

  BIDECIMAL_CALL1 (bid64_to_binary80, xd, x);
  __bid_f80_log2( rd, xd );
  __bid_f80_sub( e_bin, xd, c_one.v);
  __bid_f80_fabs( abs_e_bin, e_bin);
  if ( __bid_f80_lt( abs_e_bin, c_half.v ) )
   { BID_F80_TYPE tmp_e;
     BID_UINT64 e;
     BID_UINT64 b64 = (BID_UINT64) BID64_1;
     BIDECIMAL_CALL2 (bid64_sub, e, x, b64);
     BIDECIMAL_CALL1 (bid64_to_binary80, tmp_e, e);
     __bid_f80_sub( tmp_e, e_bin, tmp_e );
     __bid_f80_mul( tmp_e, c_1_ov_ln_2.v, tmp_e );
     __bid_f80_div( tmp_e, tmp_e, xd );
     __bid_f80_sub( rd, rd, tmp_e );
   }
  BIDECIMAL_CALL1 (binary80_to_bid64, res, rd);
  BID_RETURN (res);
}
