gonzui

    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: /* LINTLIBRARY */
   20: 
   21: #include <sys/cdefs.h>
   22: #include <float.h>
   23: #include <math.h>
   24: 
   25: #include "math_private.h"
   26: 
   27: int
   28: ilogb(double x)
   29: {
   30:         int32_t hx,lx,ix;
   31: 
   32:         GET_HIGH_WORD(hx,x);
   33:         hx &= 0x7fffffff;
   34:         if(hx<0x00100000) {
   35:             GET_LOW_WORD(lx,x);
   36:             if((hx|lx)==0) 
   37:                 return 0x80000001;    /* ilogb(0) = 0x80000001 */
   38:             else                       /* subnormal x */
   39:                 if(hx==0) {
   40:                     for (ix = -1043; lx>0; lx<<=1) ix -=1;
   41:                 } else {
   42:                     for (ix = -1022,hx<<=11; hx>0; hx<<=1) ix -=1;
   43:                 }
   44:             return ix;
   45:         }
   46:         else if (hx<0x7ff00000) return (hx>>20)-1023;
   47:         else return 0x7fffffff;
   48: }
   49: 
   50: #if     LDBL_MANT_DIG == 53
   51: #ifdef  lint
   52: /* PROTOLIB1 */
   53: int ilogbl(long double);
   54: #else   /* lint */
   55: __weak_alias(ilogbl, ilogb);
   56: #endif  /* lint */
   57: #endif  /* LDBL_MANT_DIG == 53 */