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s_scalbn.c (1909B)

      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  * scalbln(double x, long n)
     14  * scalbln(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_libm.h"
     20 #include "math_private.h"
     21 #include <limits.h>
     22 
     23 #ifdef __WATCOMC__ /* Watcom defines huge=__huge */
     24 #undef huge
     25 #endif
     26 
     27 static const double
     28 two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
     29 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
     30 huge   = 1.0e+300,
     31 tiny   = 1.0e-300;
     32 
     33 double scalbln(double x, long n)
     34 {
     35 	int32_t k, hx, lx;
     36 
     37 	EXTRACT_WORDS(hx, lx, x);
     38 	k = (hx & 0x7ff00000) >> 20; /* extract exponent */
     39 	if (k == 0) { /* 0 or subnormal x */
     40 		if ((lx | (hx & 0x7fffffff)) == 0)
     41 			return x; /* +-0 */
     42 		x *= two54;
     43 		GET_HIGH_WORD(hx, x);
     44 		k = ((hx & 0x7ff00000) >> 20) - 54;
     45 	}
     46 	if (k == 0x7ff)
     47 		return x + x; /* NaN or Inf */
     48 	k = (int32_t)(k + n);
     49 	if (k > 0x7fe)
     50 		return huge * copysign(huge, x); /* overflow */
     51 	if (n < -50000)
     52 		return tiny * copysign(tiny, x); /* underflow */
     53 	if (k > 0) { /* normal result */
     54 		SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
     55 		return x;
     56 	}
     57 	if (k <= -54) {
     58 		if (n > 50000) /* in case integer overflow in n+k */
     59 			return huge * copysign(huge, x); /* overflow */
     60 		return tiny * copysign(tiny, x); /* underflow */
     61 	}
     62 	k += 54; /* subnormal result */
     63 	SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
     64 	return x * twom54;
     65 }
     66 libm_hidden_def(scalbln)
     67 
     68 
     69 double scalbn(double x, int n)
     70 {
     71 	return scalbln(x, n);
     72 }
     73 libm_hidden_def(scalbn)