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Annotation of 43BSDReno/lib/libm/common_source/log10.c, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1985 Regents of the University of California.
                      3:  * All rights reserved.
                      4:  *
                      5:  * Redistribution and use in source and binary forms are permitted
                      6:  * provided that: (1) source distributions retain this entire copyright
                      7:  * notice and comment, and (2) distributions including binaries display
                      8:  * the following acknowledgement:  ``This product includes software
                      9:  * developed by the University of California, Berkeley and its contributors''
                     10:  * in the documentation or other materials provided with the distribution
                     11:  * and in all advertising materials mentioning features or use of this
                     12:  * software. Neither the name of the University nor the names of its
                     13:  * contributors may be used to endorse or promote products derived
                     14:  * from this software without specific prior written permission.
                     15:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
                     16:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
                     17:  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
                     18:  *
                     19:  * All recipients should regard themselves as participants in an ongoing
                     20:  * research project and hence should feel obligated to report their
                     21:  * experiences (good or bad) with these elementary function codes, using
                     22:  * the sendbug(8) program, to the authors.
                     23:  */
                     24: 
                     25: #ifndef lint
                     26: static char sccsid[] = "@(#)log10.c    5.5 (Berkeley) 6/1/90";
                     27: #endif /* not lint */
                     28: 
                     29: /* LOG10(X)
                     30:  * RETURN THE BASE 10 LOGARITHM OF x
                     31:  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
                     32:  * CODED IN C BY K.C. NG, 1/20/85; 
                     33:  * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
                     34:  * 
                     35:  * Required kernel function:
                     36:  *     log(x)
                     37:  *
                     38:  * Method :
                     39:  *                          log(x)
                     40:  *             log10(x) = ---------  or  [1/log(10)]*log(x)
                     41:  *                         log(10)
                     42:  *
                     43:  *    Note:
                     44:  *       [log(10)]   rounded to 56 bits has error  .0895  ulps,
                     45:  *       [1/log(10)] rounded to 53 bits has error  .198   ulps;
                     46:  *       therefore, for better accuracy, in VAX D format, we divide 
                     47:  *       log(x) by log(10), but in IEEE Double format, we multiply 
                     48:  *       log(x) by [1/log(10)].
                     49:  *
                     50:  * Special cases:
                     51:  *     log10(x) is NaN with signal if x < 0; 
                     52:  *     log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
                     53:  *     log10(NaN) is that NaN with no signal.
                     54:  *
                     55:  * Accuracy:
                     56:  *     log10(X) returns the exact log10(x) nearly rounded. In a test run
                     57:  *     with 1,536,000 random arguments on a VAX, the maximum observed
                     58:  *     error was 1.74 ulps (units in the last place).
                     59:  *
                     60:  * Constants:
                     61:  * The hexadecimal values are the intended ones for the following constants.
                     62:  * The decimal values may be used, provided that the compiler will convert
                     63:  * from decimal to binary accurately enough to produce the hexadecimal values
                     64:  * shown.
                     65:  */
                     66: 
                     67: #include "mathimpl.h"
                     68: 
                     69: vc(ln10hi, 2.3025850929940456790E0 ,5d8d,4113,a8ac,ddaa, 2, .935D8DDDAAA8AC)
                     70: 
                     71: ic(ivln10, 4.3429448190325181667E-1, -2, 1.BCB7B1526E50E)
                     72: 
                     73: #ifdef vccast
                     74: #define        ln10hi  vccast(ln10hi)
                     75: #endif
                     76: 
                     77: 
                     78: double log10(x)
                     79: double x;
                     80: {
                     81: #if defined(vax)||defined(tahoe)
                     82:        return(log(x)/ln10hi);
                     83: #else  /* defined(vax)||defined(tahoe) */
                     84:        return(ivln10*log(x));
                     85: #endif /* defined(vax)||defined(tahoe) */
                     86: }

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