1/* @(#)s_scalbn.c 5.1 93/09/24 */ 2/* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13#if defined(LIBM_SCCS) && !defined(lint) 14static char rcsid[] = "$NetBSD: s_scalbn.c,v 1.8 1995/05/10 20:48:08 jtc Exp $"; 15#endif 16 17/* 18 * scalbn (double x, int n) 19 * scalbn(x,n) returns x* 2**n computed by exponent 20 * manipulation rather than by actually performing an 21 * exponentiation or a multiplication. 22 */ 23 24#include "math.h" 25#include "math_private.h" 26 27#ifdef __STDC__ 28static const double 29#else 30static double 31#endif 32two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 33twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 34huge = 1.0e+300, 35tiny = 1.0e-300; 36 37#ifdef __STDC__ 38 double __scalbln (double x, long int n) 39#else 40 double __scalbln (x,n) 41 double x; long int n; 42#endif 43{ 44 int32_t k,hx,lx; 45 EXTRACT_WORDS(hx,lx,x); 46 k = (hx&0x7ff00000)>>20; /* extract exponent */ 47 if (k==0) { /* 0 or subnormal x */ 48 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 49 x *= two54; 50 GET_HIGH_WORD(hx,x); 51 k = ((hx&0x7ff00000)>>20) - 54; 52 } 53 if (k==0x7ff) return x+x; /* NaN or Inf */ 54 k = k+n; 55 if (n> 50000 || k > 0x7fe) 56 return huge*__copysign(huge,x); /* overflow */ 57 if (n< -50000) return tiny*__copysign(tiny,x); /*underflow*/ 58 if (k > 0) /* normal result */ 59 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} 60 if (k <= -54) 61 return tiny*__copysign(tiny,x); /*underflow*/ 62 k += 54; /* subnormal result */ 63 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); 64 return x*twom54; 65} 66weak_alias (__scalbln, scalbln) 67#ifdef NO_LONG_DOUBLE 68strong_alias (__scalbln, __scalblnl) 69weak_alias (__scalbln, scalblnl) 70#endif 71