log.cpp

   1 // natural logarithm
   2
   3 #include "stdafx.h"
   4 #include "defs.h"
   5
   6 void
   7 eval_log(void)
   8 {
   9         push(cadr(p1));
  10         eval();
  11         logarithm();
  12 }
  13
  14 void
  15 logarithm(void)
  16 {
  17         save();
  18         yylog();
  19         restore();
  20 }
  21
  22 void
  23 yylog(void)
  24 {
  25         double d;
  26
  27         p1 = pop();
  28
  29         if (p1 == symbol(E)) {
  30                 push_integer(1);
  31                 return;
  32         }
  33
  34         if (equaln(p1, 1)) {
  35                 push_integer(0);
  36                 return;
  37         }
  38
  39         if (isnegativenumber(p1)) {
  40                 push(p1);
  41                 negate();
  42                 logarithm();
  43                 push(imaginaryunit);
  44                 push_symbol(PI);
  45                 multiply();
  46                 add();
  47                 return;
  48         }
  49
  50         if (isdouble(p1)) {
  51                 d = log(p1->u.d);
  52                 push_double(d);
  53                 return;
  54         }
  55
  56         // rational number and not an integer?
  57
  58         if (isfraction(p1)) {
  59                 push(p1);
  60                 numerator();
  61                 logarithm();
  62                 push(p1);
  63                 denominator();
  64                 logarithm();
  65                 subtract();
  66                 return;
  67         }
  68
  69         // log(a ^ b) --> b log(a)
  70
  71         if (car(p1) == symbol(POWER)) {
  72                 push(caddr(p1));
  73                 push(cadr(p1));
  74                 logarithm();
  75                 multiply();
  76                 return;
  77         }
  78
  79         // log(a * b) --> log(a) + log(b)
  80
  81         if (car(p1) == symbol(MULTIPLY)) {
  82                 push_integer(0);
  83                 p1 = cdr(p1);
  84                 while (iscons(p1)) {
  85                         push(car(p1));
  86                         logarithm();
  87                         add();
  88                         p1 = cdr(p1);
  89                 }
  90                 return;
  91         }
  92
  93         push_symbol(LOG);
  94         push(p1);
  95         list(2);
  96 }