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      1 /* @(#)s_scalbn.c 5.1 93/09/24 */
      2 /* @(#)fdlibm.h 5.1 93/09/24 */
      3 /*
      4  * ====================================================
      5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      6  *
      7  * Developed at SunPro, a Sun Microsystems, Inc. business.
      8  * Permission to use, copy, modify, and distribute this
      9  * software is freely granted, provided that this notice
     10  * is preserved.
     11  * ====================================================
     12  */
     13 
     14 #include <sys/cdefs.h>
     15 __FBSDID("$FreeBSD$");
     16 
     17 #include <sys/types.h>
     18 #include <machine/endian.h>
     19 #include <math.h>
     20 
     21 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
     22 
     23 #if BYTE_ORDER == BIG_ENDIAN
     24 
     25 typedef union
     26 {
     27   double value;
     28   struct
     29   {
     30     u_int32_t msw;
     31     u_int32_t lsw;
     32   } parts;
     33 } ieee_double_shape_type;
     34 
     35 #endif
     36 
     37 #if BYTE_ORDER == LITTLE_ENDIAN
     38 
     39 typedef union
     40 {
     41   double value;
     42   struct
     43   {
     44     u_int32_t lsw;
     45     u_int32_t msw;
     46   } parts;
     47 } ieee_double_shape_type;
     48 
     49 #endif
     50 
     51 /* Get two 32 bit ints from a double.  */
     52 
     53 #define EXTRACT_WORDS(ix0,ix1,d)				\
     54 do {								\
     55   ieee_double_shape_type ew_u;					\
     56   ew_u.value = (d);						\
     57   (ix0) = ew_u.parts.msw;					\
     58   (ix1) = ew_u.parts.lsw;					\
     59 } while (0)
     60 
     61 /* Get the more significant 32 bit int from a double.  */
     62 
     63 #define GET_HIGH_WORD(i,d)					\
     64 do {								\
     65   ieee_double_shape_type gh_u;					\
     66   gh_u.value = (d);						\
     67   (i) = gh_u.parts.msw;						\
     68 } while (0)
     69 
     70 /* Set the more significant 32 bits of a double from an int.  */
     71 
     72 #define SET_HIGH_WORD(d,v)					\
     73 do {								\
     74   ieee_double_shape_type sh_u;					\
     75   sh_u.value = (d);						\
     76   sh_u.parts.msw = (v);						\
     77   (d) = sh_u.value;						\
     78 } while (0)
     79 
     80 
     81 static const double
     82 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
     83 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
     84 huge   = 1.0e+300,
     85 tiny   = 1.0e-300;
     86 
     87 static double
     88 _copysign(double x, double y)
     89 {
     90 	u_int32_t hx,hy;
     91 	GET_HIGH_WORD(hx,x);
     92 	GET_HIGH_WORD(hy,y);
     93 	SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
     94 	return x;
     95 }
     96 
     97 double
     98 ldexp(double x, int n)
     99 {
    100 	int32_t k,hx,lx;
    101 	EXTRACT_WORDS(hx,lx,x);
    102         k = (hx&0x7ff00000)>>20;		/* extract exponent */
    103         if (k==0) {				/* 0 or subnormal x */
    104             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
    105 	    x *= two54;
    106 	    GET_HIGH_WORD(hx,x);
    107 	    k = ((hx&0x7ff00000)>>20) - 54;
    108             if (n< -50000) return tiny*x; 	/*underflow*/
    109 	    }
    110         if (k==0x7ff) return x+x;		/* NaN or Inf */
    111         k = k+n;
    112         if (k >  0x7fe) return huge*_copysign(huge,x); /* overflow  */
    113         if (k > 0) 				/* normal result */
    114 	    {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
    115         if (k <= -54) {
    116             if (n > 50000) 	/* in case integer overflow in n+k */
    117 		return huge*_copysign(huge,x);	/*overflow*/
    118 	    else return tiny*_copysign(tiny,x); 	/*underflow*/
    119 	}
    120         k += 54;				/* subnormal result */
    121 	SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
    122         return x*twom54;
    123 }
    124