1*1e651e1eSRoland Levillain 2*1e651e1eSRoland Levillain /* @(#)s_ilogb.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 /* ieee_ilogb(double x) 15*1e651e1eSRoland Levillain * return the binary exponent of non-zero x 16*1e651e1eSRoland Levillain * ieee_ilogb(0) = 0x80000001 17*1e651e1eSRoland Levillain * ieee_ilogb(inf/NaN) = 0x7fffffff (no signal is raised) 18*1e651e1eSRoland Levillain */ 19*1e651e1eSRoland Levillain 20*1e651e1eSRoland Levillain #include "fdlibm.h" 21*1e651e1eSRoland Levillain 22*1e651e1eSRoland Levillain #ifdef __STDC__ ieee_ilogb(double x)23*1e651e1eSRoland Levillain int ieee_ilogb(double x) 24*1e651e1eSRoland Levillain #else 25*1e651e1eSRoland Levillain int ieee_ilogb(x) 26*1e651e1eSRoland Levillain double x; 27*1e651e1eSRoland Levillain #endif 28*1e651e1eSRoland Levillain { 29*1e651e1eSRoland Levillain int hx,lx,ix; 30*1e651e1eSRoland Levillain 31*1e651e1eSRoland Levillain hx = (__HI(x))&0x7fffffff; /* high word of x */ 32*1e651e1eSRoland Levillain if(hx<0x00100000) { 33*1e651e1eSRoland Levillain lx = __LO(x); 34*1e651e1eSRoland Levillain if((hx|lx)==0) 35*1e651e1eSRoland Levillain return 0x80000001; /* ieee_ilogb(0) = 0x80000001 */ 36*1e651e1eSRoland Levillain else /* subnormal x */ 37*1e651e1eSRoland Levillain if(hx==0) { 38*1e651e1eSRoland Levillain for (ix = -1043; lx>0; lx<<=1) ix -=1; 39*1e651e1eSRoland Levillain } else { 40*1e651e1eSRoland Levillain for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 41*1e651e1eSRoland Levillain } 42*1e651e1eSRoland Levillain return ix; 43*1e651e1eSRoland Levillain } 44*1e651e1eSRoland Levillain else if (hx<0x7ff00000) return (hx>>20)-1023; 45*1e651e1eSRoland Levillain else return 0x7fffffff; 46*1e651e1eSRoland Levillain } 47