s_scalbn.c revision 1.19 
1166124Srafan/* @(#)s_scalbn.c 5.1 93/09/24 */
2174993Srafan/*
3166124Srafan * ====================================================
4166124Srafan * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5166124Srafan *
6166124Srafan * Developed at SunPro, a Sun Microsystems, Inc. business.
7166124Srafan * Permission to use, copy, modify, and distribute this
8166124Srafan * software is freely granted, provided that this notice
9166124Srafan * is preserved.
10166124Srafan * ====================================================
11166124Srafan */
12166124Srafan
13166124Srafan#include <sys/cdefs.h>
14166124Srafan#if defined(LIBM_SCCS) && !defined(lint)
15166124Srafan__RCSID("$NetBSD: s_scalbn.c,v 1.19 2018/03/27 11:59:49 martin Exp $");
16166124Srafan#endif
17166124Srafan
18166124Srafan/*
19166124Srafan * scalbn (double x, int n)
20166124Srafan * scalbn(x,n) returns x* 2**n  computed by  exponent
21166124Srafan * manipulation rather than by actually performing an
22166124Srafan * exponentiation or a multiplication.
23166124Srafan */
24166124Srafan
25166124Srafan#include "namespace.h"
26166124Srafan#include "math.h"
27166124Srafan#include "math_private.h"
28174993Srafan
29166124Srafan#ifndef _LP64
3050276Speter__strong_alias(_scalbn, _scalbln)
3150276Speter#endif
3250276Speter
3350276Speter#ifndef __HAVE_LONG_DOUBLE
3450276Speter__strong_alias(_scalbnl, _scalbn)
35166124Srafan__strong_alias(_scalblnl, _scalbln)
3650276Speter__weak_alias(scalbnl, _scalbnl)
37166124Srafan__weak_alias(scalblnl, _scalblnl)
3850276Speter__weak_alias(ldexpl, _scalblnl)
3950276Speter#endif
4050276Speter
41166124Srafan#ifdef __weak_alias
42166124Srafan__weak_alias(scalbn, _scalbn)
43166124Srafan__weak_alias(scalbln, _scalbln)
4450276Speter__weak_alias(ldexp, _scalbn)
45166124Srafan#endif
4650276Speter
4750276Speterstatic const double
48166124Srafantwo54   =  0x1.0p54,	/* 0x43500000, 0x00000000 */
4950276Spetertwom54  =  0x1.0p-54,	/* 0x3C900000, 0x00000000 */
5050276Speterhuge   = 1.0e+300,
5150276Spetertiny   = 1.0e-300;
5250276Speter
5350276Speter#ifdef _LP64
54166124Srafandouble
55166124Srafanscalbn(double x, int n)
56166124Srafan{
5750276Speter	return scalbln(x, n);
58166124Srafan}
59166124Srafan#endif
6050276Speter
61166124Srafandouble
62166124Srafanscalbln(double x, long n)
63166124Srafan{
6450276Speter	int32_t k,hx,lx;
6550276Speter	EXTRACT_WORDS(hx,lx,x);
66166124Srafan        k = ((uint32_t)hx&0x7ff00000)>>20;		/* extract exponent */
67166124Srafan        if (k==0) {				/* 0 or subnormal x */
68166124Srafan            if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
69166124Srafan	    x *= two54;
70166124Srafan	    GET_HIGH_WORD(hx,x);
71166124Srafan	    k = (((uint32_t)hx&0x7ff00000)>>20) - 54;
72166124Srafan            if (n< -50000) return tiny*x; 	/*underflow*/
7350276Speter	    }
74166124Srafan        if (k==0x7ff) return x+x;		/* NaN or Inf */
75174993Srafan        k = k+n;
76174993Srafan        if (k >  0x7fe) return huge*copysign(huge,x); /* overflow  */
77174993Srafan        if (k > 0) 				/* normal result */
78174993Srafan	    {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
79174993Srafan        if (k <= -54) {
80174993Srafan            if (n > 50000) 	/* in case integer overflow in n+k */
8150276Speter		return huge*copysign(huge,x);	/*overflow*/
82166124Srafan	    else return tiny*copysign(tiny,x); 	/*underflow*/
83166124Srafan	}
84166124Srafan        k += 54;				/* subnormal result */
85166124Srafan	SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
8650276Speter        return x*twom54;
87174993Srafan}
8850276Speter