ref: 53aac62a54ebbcc1781c0000d3e2384ed038c7bb
dir: /libmath/fdlibm/s_scalbn.c/
/* derived from /netlib/fdlibm */ /* @(#)s_scalbn.c 1.3 95/01/18 */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunSoft, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* * 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" static const double two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */ twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */ Huge = 1.0e+300, tiny = 1.0e-300; double scalbn (double x, int n) { int k,hx,lx; hx = __HI(x); lx = __LO(x); k = (hx&0x7ff00000)>>20; /* extract exponent */ if (k==0) { /* 0 or subnormal x */ if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */ x *= two54; hx = __HI(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 */ {__HI(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 */ __HI(x) = (hx&0x800fffff)|(k<<20); return x*twom54; }