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       ---
       s_logb.c (959B)
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            1 /* @(#)s_logb.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 #ifndef lint
           14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_logb.c,v 1.9 2003/07/23 04:53:46 peter Exp $";
           15 #endif
           16 
           17 /*
           18  * double logb(x)
           19  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
           20  * Use ilogb instead.
           21  */
           22 
           23 #include "math.h"
           24 #include "math_private.h"
           25 
           26 double
           27 logb(double x)
           28 {
           29         int32_t lx,ix;
           30         EXTRACT_WORDS(ix,lx,x);
           31         ix &= 0x7fffffff;                        /* high |x| */
           32         if((ix|lx)==0) return -1.0/fabs(x);
           33         if(ix>=0x7ff00000) return x*x;
           34         if((ix>>=20)==0)                         /* IEEE 754 logb */
           35                 return -1022.0;
           36         else
           37                 return (double) (ix-1023);
           38 }