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Annotation of 43BSDTahoe/cci/libM/logd.c, revision 1.1.1.1

1.1       root        1: /*     @(#)log.c       4.1     12/25/82        */
                      2: 
                      3: /*
                      4:  * log returns the natural logarithm of its floating
                      5:  * point argument.
                      6:  *
                      7:  * New version by Les Powers (3/31/85).
                      8:  */
                      9: 
                     10: 
                     11: #include <errno.h>
                     12: #include <math.h>
                     13: #include "logd.h"
                     14: 
                     15: 
                     16: static double  log2    = 0.693147180559945309e0;
                     17: static double  recip_ln10      = 1./2.302585092994045684;
                     18: static double  p1      = 1.;
                     19: static double  p2      = -.5;
                     20: static double  p3      = 1./3.;
                     21: static double  p4      = -1./4.;
                     22: 
                     23: int    errno;
                     24: 
                     25: 
                     26: double
                     27: log(arg)
                     28: double arg;
                     29: {
                     30:        double z;
                     31:        union {
                     32:          double d;
                     33:          struct {
                     34:            unsigned i0;
                     35:            unsigned i1;
                     36:          } i;
                     37:          struct {
                     38:            unsigned char b0;
                     39:            unsigned char b1;
                     40:            unsigned char b2;
                     41:            unsigned char b3;
                     42:          } b;
                     43:        } f0,f1,a0;
                     44:        register int ta1;
                     45:        if (arg <= 0.) {
                     46:                errno = EDOM;
                     47:                return(-HUGE);
                     48:        }
                     49:        f1.d  = arg;
                     50:        f0.i.i0 = f1.i.i0 + f1.i.i0;
                     51:        if ( f1.i.i0 >= 0x40800000 ) {
                     52:          f1.i.i0 = (f1.i.i0 & 0x007fffff) | 0x40800000;
                     53:          a0.i.i0 =  f1.i.i0 & 0x40ff8000;
                     54:          a0.i.i1 = 0;
                     55:          f1.d    =  (f1.d - a0.d) * rp0[f0.b.b1];
                     56:          ta1 = f1.d;
                     57:          z  = (f1.d - ta1) * rp1[ta1];
                     58:          return( z*(p1+z*(p2+z*(p3+z*p4))) +
                     59:                lp1[ta1] + lp0[f0.b.b1] + le[f0.b.b0] );
                     60:        }
                     61:        else {
                     62:          f1.i.i0 = (f1.i.i0 & 0x007fffff) | 0x40000000;
                     63:          a0.i.i0 = (f1.i.i0 & 0x40ff8000) + 0x00008000;
                     64:          a0.i.i1 = 0;
                     65:          f1.d    = (a0.d - f1.d) * rn0[f0.b.b1];
                     66:          ta1 = f1.d;
                     67:          z  = (ta1-f1.d) * rn1[ta1];
                     68:          return( z*(p1+z*(p2+z*(p3+z*p4))) +
                     69:                ln1[ta1] + ln0[f0.b.b1] + le[f0.b.b0] );
                     70:        }
                     71: }
                     72: 
                     73: double
                     74: log10(arg)
                     75: double arg;
                     76: {
                     77:        return(log(arg)*recip_ln10);
                     78: }

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