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- // natural logarithm
- #include "stdafx.h"
- #include "defs.h"
- void
- eval_log(void)
- {
- push(cadr(p1));
- eval();
- logarithm();
- }
- void
- logarithm(void)
- {
- save();
- yylog();
- restore();
- }
- void
- yylog(void)
- {
- double d;
- p1 = pop();
- if (p1 == symbol(E)) {
- push_integer(1);
- return;
- }
- if (equaln(p1, 1)) {
- push_integer(0);
- return;
- }
- if (isnegativenumber(p1)) {
- push(p1);
- negate();
- logarithm();
- push(imaginaryunit);
- push_symbol(PI);
- multiply();
- add();
- return;
- }
- if (isdouble(p1)) {
- d = log(p1->u.d);
- push_double(d);
- return;
- }
- // rational number and not an integer?
- if (isfraction(p1)) {
- push(p1);
- numerator();
- logarithm();
- push(p1);
- denominator();
- logarithm();
- subtract();
- return;
- }
- // log(a ^ b) --> b log(a)
- if (car(p1) == symbol(POWER)) {
- push(caddr(p1));
- push(cadr(p1));
- logarithm();
- multiply();
- return;
- }
- // log(a * b) --> log(a) + log(b)
- if (car(p1) == symbol(MULTIPLY)) {
- push_integer(0);
- p1 = cdr(p1);
- while (iscons(p1)) {
- push(car(p1));
- logarithm();
- add();
- p1 = cdr(p1);
- }
- return;
- }
- push_symbol(LOG);
- push(p1);
- list(2);
- }
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