Return to log10.c CVS log

Up to [CSRG BSD Unix] / 43BSD / usr.lib / libm

Annotation of 43BSD/usr.lib/libm/log10.c, revision 1.1

1.1     ! root        1: /* 
        !             2:  * Copyright (c) 1985 Regents of the University of California.
        !             3:  * 
        !             4:  * Use and reproduction of this software are granted  in  accordance  with
        !             5:  * the terms and conditions specified in  the  Berkeley  Software  License
        !             6:  * Agreement (in particular, this entails acknowledgement of the programs'
        !             7:  * source, and inclusion of this notice) with the additional understanding
        !             8:  * that  all  recipients  should regard themselves as participants  in  an
        !             9:  * ongoing  research  project and hence should  feel  obligated  to report
        !            10:  * their  experiences (good or bad) with these elementary function  codes,
        !            11:  * using "sendbug 4bsd-bugs@BERKELEY", to the authors.
        !            12:  */
        !            13: 
        !            14: #ifndef lint
        !            15: static char sccsid[] = "@(#)log10.c    1.2 (Berkeley) 8/21/85";
        !            16: #endif not lint
        !            17: 
        !            18: /* LOG10(X)
        !            19:  * RETURN THE BASE 10 LOGARITHM OF x
        !            20:  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
        !            21:  * CODED IN C BY K.C. NG, 1/20/85; 
        !            22:  * REVISED BY K.C. NG on 1/23/85, 3/7/85, 4/16/85.
        !            23:  * 
        !            24:  * Required kernel function:
        !            25:  *     log(x)
        !            26:  *
        !            27:  * Method :
        !            28:  *                          log(x)
        !            29:  *             log10(x) = ---------  or  [1/log(10)]*log(x)
        !            30:  *                         log(10)
        !            31:  *
        !            32:  *    Note:
        !            33:  *       [log(10)]   rounded to 56 bits has error  .0895  ulps,
        !            34:  *       [1/log(10)] rounded to 53 bits has error  .198   ulps;
        !            35:  *       therefore, for better accuracy, in VAX D format, we divide 
        !            36:  *       log(x) by log(10), but in IEEE Double format, we multiply 
        !            37:  *       log(x) by [1/log(10)].
        !            38:  *
        !            39:  * Special cases:
        !            40:  *     log10(x) is NaN with signal if x < 0; 
        !            41:  *     log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
        !            42:  *     log10(NaN) is that NaN with no signal.
        !            43:  *
        !            44:  * Accuracy:
        !            45:  *     log10(X) returns the exact log10(x) nearly rounded. In a test run
        !            46:  *     with 1,536,000 random arguments on a VAX, the maximum observed
        !            47:  *     error was 1.74 ulps (units in the last place).
        !            48:  *
        !            49:  * Constants:
        !            50:  * The hexadecimal values are the intended ones for the following constants.
        !            51:  * The decimal values may be used, provided that the compiler will convert
        !            52:  * from decimal to binary accurately enough to produce the hexadecimal values
        !            53:  * shown.
        !            54:  */
        !            55: 
        !            56: #ifdef VAX     /* VAX D format (56 bits) */
        !            57: /* static double */
        !            58: /* ln10hi =  2.3025850929940456790E0     ; Hex   2^  2   *  .935D8DDDAAA8AC */
        !            59: static long    ln10hix[] = { 0x5d8d4113, 0xa8acddaa};
        !            60: #define   ln10hi    (*(double*)ln10hix)
        !            61: #else  /* IEEE double */
        !            62: static double
        !            63: ivln10 =  4.3429448190325181667E-1    ; /*Hex   2^ -2   *  1.BCB7B1526E50E */
        !            64: #endif
        !            65: 
        !            66: double log10(x)
        !            67: double x;
        !            68: {
        !            69:        double log();
        !            70: 
        !            71: #ifdef VAX
        !            72:        return(log(x)/ln10hi);
        !            73: #else  /* IEEE double */
        !            74:        return(ivln10*log(x));
        !            75: #endif
        !            76: }

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.