1*37da2899SCharles.Forsyth /* derived from /netlib/fdlibm */ 2*37da2899SCharles.Forsyth 3*37da2899SCharles.Forsyth /* @(#)s_scalbn.c 1.3 95/01/18 */ 4*37da2899SCharles.Forsyth /* 5*37da2899SCharles.Forsyth * ==================================================== 6*37da2899SCharles.Forsyth * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 7*37da2899SCharles.Forsyth * 8*37da2899SCharles.Forsyth * Developed at SunSoft, a Sun Microsystems, Inc. business. 9*37da2899SCharles.Forsyth * Permission to use, copy, modify, and distribute this 10*37da2899SCharles.Forsyth * software is freely granted, provided that this notice 11*37da2899SCharles.Forsyth * is preserved. 12*37da2899SCharles.Forsyth * ==================================================== 13*37da2899SCharles.Forsyth */ 14*37da2899SCharles.Forsyth 15*37da2899SCharles.Forsyth /* 16*37da2899SCharles.Forsyth * scalbn (double x, int n) 17*37da2899SCharles.Forsyth * scalbn(x,n) returns x* 2**n computed by exponent 18*37da2899SCharles.Forsyth * manipulation rather than by actually performing an 19*37da2899SCharles.Forsyth * exponentiation or a multiplication. 20*37da2899SCharles.Forsyth */ 21*37da2899SCharles.Forsyth 22*37da2899SCharles.Forsyth #include "fdlibm.h" 23*37da2899SCharles.Forsyth 24*37da2899SCharles.Forsyth static const double 25*37da2899SCharles.Forsyth two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 26*37da2899SCharles.Forsyth twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 27*37da2899SCharles.Forsyth Huge = 1.0e+300, 28*37da2899SCharles.Forsyth tiny = 1.0e-300; 29*37da2899SCharles.Forsyth scalbn(double x,int n)30*37da2899SCharles.Forsyth double scalbn (double x, int n) 31*37da2899SCharles.Forsyth { 32*37da2899SCharles.Forsyth int k,hx,lx; 33*37da2899SCharles.Forsyth hx = __HI(x); 34*37da2899SCharles.Forsyth lx = __LO(x); 35*37da2899SCharles.Forsyth k = (hx&0x7ff00000)>>20; /* extract exponent */ 36*37da2899SCharles.Forsyth if (k==0) { /* 0 or subnormal x */ 37*37da2899SCharles.Forsyth if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 38*37da2899SCharles.Forsyth x *= two54; 39*37da2899SCharles.Forsyth hx = __HI(x); 40*37da2899SCharles.Forsyth k = ((hx&0x7ff00000)>>20) - 54; 41*37da2899SCharles.Forsyth if (n< -50000) return tiny*x; /*underflow*/ 42*37da2899SCharles.Forsyth } 43*37da2899SCharles.Forsyth if (k==0x7ff) return x+x; /* NaN or Inf */ 44*37da2899SCharles.Forsyth k = k+n; 45*37da2899SCharles.Forsyth if (k > 0x7fe) return Huge*copysign(Huge,x); /* overflow */ 46*37da2899SCharles.Forsyth if (k > 0) /* normal result */ 47*37da2899SCharles.Forsyth {__HI(x) = (hx&0x800fffff)|(k<<20); return x;} 48*37da2899SCharles.Forsyth if (k <= -54) 49*37da2899SCharles.Forsyth if (n > 50000) /* in case integer overflow in n+k */ 50*37da2899SCharles.Forsyth return Huge*copysign(Huge,x); /*overflow*/ 51*37da2899SCharles.Forsyth else return tiny*copysign(tiny,x); /*underflow*/ 52*37da2899SCharles.Forsyth k += 54; /* subnormal result */ 53*37da2899SCharles.Forsyth __HI(x) = (hx&0x800fffff)|(k<<20); 54*37da2899SCharles.Forsyth return x*twom54; 55*37da2899SCharles.Forsyth } 56