1  /*
       2   * ====================================================
       3   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       4   *
       5   * Developed at SunPro, a Sun Microsystems, Inc. business.
       6   * Permission to use, copy, modify, and distribute this
       7   * software is freely granted, provided that this notice
       8   * is preserved.
       9   * ====================================================
      10   */
      11  
      12  /*
      13   * scalbn (double x, int n)
      14   * scalbn(x,n) returns x* 2**n  computed by  exponent
      15   * manipulation rather than by actually performing an
      16   * exponentiation or a multiplication.
      17   */
      18  
      19  #include <math.h>
      20  #include <math_private.h>
      21  
      22  static const double
      23  two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
      24  twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
      25  huge   = 1.0e+300,
      26  tiny   = 1.0e-300;
      27  
      28  double
      29  __scalbn (double x, int n)
      30  {
      31  	int64_t ix;
      32  	int64_t k;
      33  	EXTRACT_WORDS64(ix,x);
      34  	k = (ix >> 52) & 0x7ff;			/* extract exponent */
      35  	if (__builtin_expect(k==0, 0)) {	/* 0 or subnormal x */
      36  	    if ((ix & UINT64_C(0xfffffffffffff))==0) return x; /* +-0 */
      37  	    x *= two54;
      38  	    EXTRACT_WORDS64(ix,x);
      39  	    k = ((ix >> 52) & 0x7ff) - 54;
      40  	    }
      41  	if (__builtin_expect(k==0x7ff, 0)) return x+x;	/* NaN or Inf */
      42  	if (__builtin_expect(n< -50000, 0))
      43  	  return tiny*copysign(tiny,x); /*underflow*/
      44  	if (__builtin_expect(n> 50000 || k+n > 0x7fe, 0))
      45  	  return huge*copysign(huge,x); /* overflow  */
      46  	/* Now k and n are bounded we know that k = k+n does not
      47  	   overflow.  */
      48  	k = k+n;
      49  	if (__builtin_expect(k > 0, 1))		/* normal result */
      50  	    {INSERT_WORDS64(x,(ix&UINT64_C(0x800fffffffffffff))|(k<<52));
      51  	      return x;}
      52  	if (k <= -54)
      53  	  return tiny*copysign(tiny,x);	/*underflow*/
      54  	k += 54;				/* subnormal result */
      55  	INSERT_WORDS64(x,(ix&INT64_C(0x800fffffffffffff))|(k<<52));
      56  	return x*twom54;
      57  }
      58  #ifdef NO_LONG_DOUBLE
      59  strong_alias (__scalbn, __scalbnl)
      60  #endif