/* @(#)s_scalbn.c 5.1 93/09/24 */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* FUNCTION <<scalbn>>, <<scalbnf>>---scale by integer INDEX scalbn INDEX scalbnf ANSI_SYNOPSIS #include <math.h> double scalbn(double <[x]>, int <[y]>); float scalbnf(float <[x]>, int <[y]>); TRAD_SYNOPSIS #include <math.h> double scalbn(<[x]>,<[y]>) double <[x]>; int <[y]>; float scalbnf(<[x]>,<[y]>) float <[x]>; int <[y]>; DESCRIPTION <<scalbn>> and <<scalbnf>> scale <[x]> by <[n]>, returning <[x]> times 2 to the power <[n]>. The result is computed by manipulating the exponent, rather than by actually performing an exponentiation or multiplication. RETURNS <[x]> times 2 to the power <[n]>. PORTABILITY Neither <<scalbn>> nor <<scalbnf>> is required by ANSI C or by the System V Interface Definition (Issue 2). */ /* * scalbn (double x, int n) * scalbn(x,n) returns x* 2**n computed by exponent * manipulation rather than by actually performing an * exponentiation or a multiplication. */ #include "fdlibm.h" #ifndef _DOUBLE_IS_32BITS #ifdef __STDC__ static const double #else static double #endif two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ huge = 1.0e+300, tiny = 1.0e-300; #ifdef __STDC__ double scalbn (double x, int n) #else double scalbn (x,n) double x; int n; #endif { int32_t k,hx,lx; EXTRACT_WORDS(hx,lx,x); k = (hx&0x7ff00000)>>20; /* extract exponent */ if (k==0) { /* 0 or subnormal x */ if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ x *= two54; GET_HIGH_WORD(hx,x); k = ((hx&0x7ff00000)>>20) - 54; if (n< -50000) return tiny*x; /*underflow*/ } if (k==0x7ff) return x+x; /* NaN or Inf */ k = k+n; if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */ if (k > 0) /* normal result */ {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;} if (k <= -54) { if (n > 50000) /* in case integer overflow in n+k */ return huge*copysign(huge,x); /*overflow*/ else return tiny*copysign(tiny,x); /*underflow*/ } k += 54; /* subnormal result */ SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x*twom54; } #endif /* _DOUBLE_IS_32BITS */