src/libm/s_scalbn.c
changeset 11683 48bcba563d9c
parent 7678 286c42d7c5ed
child 11684 eccdf37f8996
equal deleted inserted replaced
11682:b26412a89fbb 11683:48bcba563d9c
     1 /* @(#)s_scalbn.c 5.1 93/09/24 */
       
     2 /*
     1 /*
     3  * ====================================================
     2  * ====================================================
     4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     5  *
     4  *
     6  * Developed at SunPro, a Sun Microsystems, Inc. business.
     5  * Developed at SunPro, a Sun Microsystems, Inc. business.
     8  * software is freely granted, provided that this notice
     7  * software is freely granted, provided that this notice
     9  * is preserved.
     8  * is preserved.
    10  * ====================================================
     9  * ====================================================
    11  */
    10  */
    12 
    11 
    13 #if defined(LIBM_SCCS) && !defined(lint)
       
    14 static const char rcsid[] =
       
    15     "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $";
       
    16 #endif
       
    17 
       
    18 /*
    12 /*
    19  * scalbn (double x, int n)
    13  * scalbln(double x, long n)
    20  * scalbn(x,n) returns x* 2**n  computed by  exponent
    14  * scalbln(x,n) returns x * 2**n computed by exponent
    21  * manipulation rather than by actually performing an
    15  * manipulation rather than by actually performing an
    22  * exponentiation or a multiplication.
    16  * exponentiation or a multiplication.
    23  */
    17  */
    24 
    18 
    25 #include "math_libm.h"
    19 #include "math_libm.h"
    26 #include "math_private.h"
    20 #include "math_private.h"
       
    21 #include <limits.h>
    27 
    22 
    28 libm_hidden_proto(copysign)
    23 static const double
    29 #ifdef __STDC__
    24 two54  = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
    30      static const double
    25 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
       
    26 huge   = 1.0e+300,
       
    27 tiny   = 1.0e-300;
       
    28 
       
    29 double scalbln(double x, long n)
       
    30 {
       
    31 	int32_t k, hx, lx;
       
    32 
       
    33 	EXTRACT_WORDS(hx, lx, x);
       
    34 	k = (hx & 0x7ff00000) >> 20; /* extract exponent */
       
    35 	if (k == 0) { /* 0 or subnormal x */
       
    36 		if ((lx | (hx & 0x7fffffff)) == 0)
       
    37 			return x; /* +-0 */
       
    38 		x *= two54;
       
    39 		GET_HIGH_WORD(hx, x);
       
    40 		k = ((hx & 0x7ff00000) >> 20) - 54;
       
    41 	}
       
    42 	if (k == 0x7ff)
       
    43 		return x + x; /* NaN or Inf */
       
    44 	k = k + n;
       
    45 	if (k > 0x7fe)
       
    46 		return huge * copysign(huge, x); /* overflow */
       
    47 	if (n < -50000)
       
    48 		return tiny * copysign(tiny, x); /* underflow */
       
    49 	if (k > 0) { /* normal result */
       
    50 		SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    51 		return x;
       
    52 	}
       
    53 	if (k <= -54) {
       
    54 		if (n > 50000) /* in case integer overflow in n+k */
       
    55 			return huge * copysign(huge, x); /* overflow */
       
    56 		return tiny * copysign(tiny, x); /* underflow */
       
    57 	}
       
    58 	k += 54; /* subnormal result */
       
    59 	SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    60 	return x * twom54;
       
    61 }
       
    62 libm_hidden_def(scalbln)
       
    63 
       
    64 #if LONG_MAX == INT_MAX
       
    65 /* strong_alias(scalbln, scalbn) - "error: conflicting types for 'scalbn'"
       
    66  * because it tries to declare "typeof(scalbln) scalbn;"
       
    67  * which tries to give "long" parameter to scalbn.
       
    68  * Doing it by hand:
       
    69  */
       
    70 __typeof(scalbn) scalbn __attribute__((alias("scalbln")));
    31 #else
    71 #else
    32      static double
    72 double scalbn(double x, int n)
       
    73 {
       
    74 	return scalbln(x, n);
       
    75 }
    33 #endif
    76 #endif
    34        two54 = 1.80143985094819840000e+16,      /* 0x43500000, 0x00000000 */
       
    35          twom54 = 5.55111512312578270212e-17,   /* 0x3C900000, 0x00000000 */
       
    36          huge_val = 1.0e+300, tiny = 1.0e-300;
       
    37 
       
    38 libm_hidden_proto(scalbn)
       
    39 #ifdef __STDC__
       
    40      double scalbn(double x, int n)
       
    41 #else
       
    42      double scalbn(x, n)
       
    43      double x;
       
    44      int n;
       
    45 #endif
       
    46 {
       
    47     int32_t k, hx, lx;
       
    48     EXTRACT_WORDS(hx, lx, x);
       
    49     k = (hx & 0x7ff00000) >> 20;        /* extract exponent */
       
    50     if (k == 0) {               /* 0 or subnormal x */
       
    51         if ((lx | (hx & 0x7fffffff)) == 0)
       
    52             return x;           /* +-0 */
       
    53         x *= two54;
       
    54         GET_HIGH_WORD(hx, x);
       
    55         k = ((hx & 0x7ff00000) >> 20) - 54;
       
    56         if (n < -50000)
       
    57             return tiny * x;    /* underflow */
       
    58     }
       
    59     if (k == 0x7ff)
       
    60         return x + x;           /* NaN or Inf */
       
    61     k = k + n;
       
    62     if (k > 0x7fe)
       
    63         return huge_val * copysign(huge_val, x);        /* overflow  */
       
    64     if (k > 0) {                /* normal result */
       
    65         SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    66         return x;
       
    67     }
       
    68     if (k <= -54) {
       
    69         if (n > 50000)          /* in case integer overflow in n+k */
       
    70             return huge_val * copysign(huge_val, x);    /* overflow */
       
    71         else
       
    72             return tiny * copysign(tiny, x);    /* underflow */
       
    73     }
       
    74     k += 54;                    /* subnormal result */
       
    75     SET_HIGH_WORD(x, (hx & 0x800fffff) | (k << 20));
       
    76     return x * twom54;
       
    77 }
       
    78 
       
    79 libm_hidden_def(scalbn)
    77 libm_hidden_def(scalbn)