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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 
     16 #include <sys/types.h>
     17 #include <endian.h>
     18 #include <math.h>
     19 
     20 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
     21 
     22 #if BYTE_ORDER == BIG_ENDIAN
     23 
     24 typedef union
     25 {
     26   double value;
     27   struct
     28   {
     29     u_int32_t msw;
     30     u_int32_t lsw;
     31   } parts;
     32 } ieee_double_shape_type;
     33 
     34 #endif
     35 
     36 #if BYTE_ORDER == LITTLE_ENDIAN
     37 
     38 typedef union
     39 {
     40   double value;
     41   struct
     42   {
     43     u_int32_t lsw;
     44     u_int32_t msw;
     45   } parts;
     46 } ieee_double_shape_type;
     47 
     48 #endif
     49 
     50 /* Get two 32 bit ints from a double.  */
     51 
     52 #define EXTRACT_WORDS(ix0,ix1,d)				\
     53 do {								\
     54   ieee_double_shape_type ew_u;					\
     55   ew_u.value = (d);						\
     56   (ix0) = ew_u.parts.msw;					\
     57   (ix1) = ew_u.parts.lsw;					\
     58 } while (0)
     59 
     60 /* Get the more significant 32 bit int from a double.  */
     61 
     62 #define GET_HIGH_WORD(i,d)					\
     63 do {								\
     64   ieee_double_shape_type gh_u;					\
     65   gh_u.value = (d);						\
     66   (i) = gh_u.parts.msw;						\
     67 } while (0)
     68 
     69 /* Set the more significant 32 bits of a double from an int.  */
     70 
     71 #define SET_HIGH_WORD(d,v)					\
     72 do {								\
     73   ieee_double_shape_type sh_u;					\
     74   sh_u.value = (d);						\
     75   sh_u.parts.msw = (v);						\
     76   (d) = sh_u.value;						\
     77 } while (0)
     78 
     79 
     80 static const double
     81 two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
     82 twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
     83 huge   = 1.0e+300,
     84 tiny   = 1.0e-300;
     85 
     86 static double
     87 _copysign(double x, double y)
     88 {
     89 	u_int32_t hx,hy;
     90 	GET_HIGH_WORD(hx,x);
     91 	GET_HIGH_WORD(hy,y);
     92 	SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
     93 	return x;
     94 }
     95 
     96 double
     97 ldexp(double x, int n)
     98 {
     99 	int32_t k,hx,lx;
    100 	EXTRACT_WORDS(hx,lx,x);
    101         k = (hx&0x7ff00000)>>20;		/* extract exponent */
    102         if (k==0) {				/* 0 or subnormal x */
    103             if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
    104 	    x *= two54;
    105 	    GET_HIGH_WORD(hx,x);
    106 	    k = ((hx&0x7ff00000)>>20) - 54;
    107             if (n< -50000) return tiny*x; 	/*underflow*/
    108 	    }
    109         if (k==0x7ff) return x+x;		/* NaN or Inf */
    110         k = k+n;
    111         if (k >  0x7fe) return huge*_copysign(huge,x); /* overflow  */
    112         if (k > 0) 				/* normal result */
    113 	    {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
    114         if (k <= -54) {
    115             if (n > 50000) 	/* in case integer overflow in n+k */
    116 		return huge*_copysign(huge,x);	/*overflow*/
    117 	    else return tiny*_copysign(tiny,x); 	/*underflow*/
    118 	}
    119         k += 54;				/* subnormal result */
    120 	SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
    121         return x*twom54;
    122 }
    123