1 /* @(#)s_ilogb.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 /* ilogb(double x) 14 * return the binary exponent of non-zero x 15 * ilogb(0) = 0x80000001 16 * ilogb(inf/NaN) = 0x7fffffff (no signal is raised) 17 */ 18 19 #include <sys/cdefs.h> 20 #include <float.h> 21 #include <math.h> 22 23 #include "math_private.h" 24 25 int 26 ilogb(double x) 27 { 28 int32_t hx,lx,ix; 29 30 GET_HIGH_WORD(hx,x); 31 hx &= 0x7fffffff; 32 if(hx<0x00100000) { 33 GET_LOW_WORD(lx,x); 34 if((hx|lx)==0) 35 return 0x80000001; /* ilogb(0) = 0x80000001 */ 36 else /* subnormal x */ 37 if(hx==0) { 38 for (ix = -1043; lx>0; lx<<=1) ix -=1; 39 } else { 40 for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1; 41 } 42 return ix; 43 } 44 else if (hx<0x7ff00000) return (hx>>20)-1023; 45 else return 0x7fffffff; 46 } 47 48 #if LDBL_MANT_DIG == 53 49 #ifdef __weak_alias 50 __weak_alias(ilogbl, ilogb); 51 #endif /* __weak_alias */ 52 #endif /* LDBL_MANT_DIG == 53 */ 53