dirac.cpp

   1 //-----------------------------------------------------------------------------
   2 //
   3 //      Author : philippe.billet@noos.fr
   4 //
   5 //      Dirac function dirac(x)
   6 //      dirac(-x)=dirac(x)
   7 //  dirac(b-a)=dirac(a-b)
   8 //-----------------------------------------------------------------------------
   9
  10 #include "stdafx.h"
  11 #include "defs.h"
  12 static void ydirac(void);
  13
  14 void
  15 eval_dirac(void)
  16 {
  17         push(cadr(p1));
  18         eval();
  19         dirac();
  20 }
  21
  22 void
  23 dirac(void)
  24 {
  25         save();
  26         ydirac();
  27         restore();
  28 }
  29
  30 #define X p1
  31
  32 static void
  33 ydirac(void)
  34 {
  35
  36         X = pop();
  37
  38
  39
  40         if (isdouble(X)) {
  41                 if (X->u.d == 0)
  42                         {push_integer(1);
  43                          return;}
  44                 else
  45                         {push_integer(0);
  46                          return;}
  47         }
  48
  49         if (isrational(X)) {
  50                 if (MZERO(mmul(X->u.q.a,X->u.q.b)))
  51                         {push_integer(1);
  52                          return;}
  53                 else
  54                         {push_integer(0);
  55                          return;}
  56
  57         }
  58
  59         if (car(X) == symbol(POWER)) {
  60                 push_symbol(DIRAC);
  61                 push(cadr(X));
  62                 list(2);
  63                 return;
  64         }
  65
  66         if (isnegativeterm(X)) {
  67                 push_symbol(DIRAC);
  68                 push(X);
  69                 negate();
  70                 list(2);
  71                 return;
  72         }
  73
  74         if (isnegativeterm(p1) || (car(p1) == symbol(ADD) && isnegativeterm(cadr(p1)))) {
  75                 push(p1);
  76                 negate();
  77                 p1 = pop();
  78         }
  79
  80
  81         push_symbol(DIRAC);
  82         push(X);
  83         list(2);
  84 }
  85
  86 #if SELFTEST
  87
  88 static char *s[] = {
  89
  90
  91         "dirac(-x)",
  92         "dirac(x)",
  93 };
  94
  95 void
  96 test_dirac(void)
  97 {
  98         test(__FILE__, s, sizeof s / sizeof (char *));
  99 }
 100
 101 #endif