1*1e651e1eSRoland Levillain 2*1e651e1eSRoland Levillain /* @(#)s_scalbn.c 1.3 95/01/18 */ 3*1e651e1eSRoland Levillain /* 4*1e651e1eSRoland Levillain * ==================================================== 5*1e651e1eSRoland Levillain * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6*1e651e1eSRoland Levillain * 7*1e651e1eSRoland Levillain * Developed at SunSoft, a Sun Microsystems, Inc. business. 8*1e651e1eSRoland Levillain * Permission to use, copy, modify, and distribute this 9*1e651e1eSRoland Levillain * software is freely granted, provided that this notice 10*1e651e1eSRoland Levillain * is preserved. 11*1e651e1eSRoland Levillain * ==================================================== 12*1e651e1eSRoland Levillain */ 13*1e651e1eSRoland Levillain 14*1e651e1eSRoland Levillain /* 15*1e651e1eSRoland Levillain * ieee_scalbn (double x, int n) 16*1e651e1eSRoland Levillain * ieee_scalbn(x,n) returns x* 2**n computed by exponent 17*1e651e1eSRoland Levillain * manipulation rather than by actually performing an 18*1e651e1eSRoland Levillain * exponentiation or a multiplication. 19*1e651e1eSRoland Levillain */ 20*1e651e1eSRoland Levillain 21*1e651e1eSRoland Levillain #include "fdlibm.h" 22*1e651e1eSRoland Levillain 23*1e651e1eSRoland Levillain #ifdef __STDC__ 24*1e651e1eSRoland Levillain static const double 25*1e651e1eSRoland Levillain #else 26*1e651e1eSRoland Levillain static double 27*1e651e1eSRoland Levillain #endif 28*1e651e1eSRoland Levillain two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ 29*1e651e1eSRoland Levillain twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ 30*1e651e1eSRoland Levillain huge = 1.0e+300, 31*1e651e1eSRoland Levillain tiny = 1.0e-300; 32*1e651e1eSRoland Levillain 33*1e651e1eSRoland Levillain #ifdef __STDC__ ieee_scalbn(double x,int n)34*1e651e1eSRoland Levillain double ieee_scalbn (double x, int n) 35*1e651e1eSRoland Levillain #else 36*1e651e1eSRoland Levillain double ieee_scalbn (x,n) 37*1e651e1eSRoland Levillain double x; int n; 38*1e651e1eSRoland Levillain #endif 39*1e651e1eSRoland Levillain { 40*1e651e1eSRoland Levillain int k,hx,lx; 41*1e651e1eSRoland Levillain hx = __HI(x); 42*1e651e1eSRoland Levillain lx = __LO(x); 43*1e651e1eSRoland Levillain k = (hx&0x7ff00000)>>20; /* extract exponent */ 44*1e651e1eSRoland Levillain if (k==0) { /* 0 or subnormal x */ 45*1e651e1eSRoland Levillain if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ 46*1e651e1eSRoland Levillain x *= two54; 47*1e651e1eSRoland Levillain hx = __HI(x); 48*1e651e1eSRoland Levillain k = ((hx&0x7ff00000)>>20) - 54; 49*1e651e1eSRoland Levillain if (n< -50000) return tiny*x; /*underflow*/ 50*1e651e1eSRoland Levillain } 51*1e651e1eSRoland Levillain if (k==0x7ff) return x+x; /* NaN or Inf */ 52*1e651e1eSRoland Levillain k = k+n; 53*1e651e1eSRoland Levillain if (k > 0x7fe) return huge*ieee_copysign(huge,x); /* overflow */ 54*1e651e1eSRoland Levillain if (k > 0) /* normal result */ 55*1e651e1eSRoland Levillain {__HI(x) = (hx&0x800fffff)|(k<<20); return x;} 56*1e651e1eSRoland Levillain if (k <= -54) 57*1e651e1eSRoland Levillain if (n > 50000) /* in case integer overflow in n+k */ 58*1e651e1eSRoland Levillain return huge*ieee_copysign(huge,x); /*overflow*/ 59*1e651e1eSRoland Levillain else return tiny*ieee_copysign(tiny,x); /*underflow*/ 60*1e651e1eSRoland Levillain k += 54; /* subnormal result */ 61*1e651e1eSRoland Levillain __HI(x) = (hx&0x800fffff)|(k<<20); 62*1e651e1eSRoland Levillain return x*twom54; 63*1e651e1eSRoland Levillain } 64