1 /* derived from /netlib/fdlibm */ 2 3 /* @(#)s_ilogb.c 1.3 95/01/18 */ 4 /* 5 * ==================================================== 6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 7 * 8 * Developed at SunSoft, a Sun Microsystems, Inc. business. 9 * Permission to use, copy, modify, and distribute this 10 * software is freely granted, provided that this notice 11 * is preserved. 12 * ==================================================== 13 */ 14 15 /* ilogb(double x) 16 * return the binary exponent of non-zero x 17 * ilogb(0) = 0x80000001 18 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) 19 */ 20 21 #include "fdlibm.h" 22 ilogb(double x)23 int ilogb(double x) 24 { 25 int hx,lx,ix; 26 27 hx = (__HI(x))&0x7fffffff; /* high word of x */ 28 if(hx<0x00100000) { 29 lx = __LO(x); 30 if((hx|lx)==0) 31 return 0x80000001; /* ilogb(0) = 0x80000001 */ 32 else /* subnormal x */ 33 if(hx==0) { 34 for (ix = -1043; lx>0; lx<<=1) ix -=1; 35 } else { 36 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 37 } 38 return ix; 39 } 40 else if (hx<0x7ff00000) return (hx>>20)-1023; 41 else return 0x7fffffff; 42 } 43