+/* quit function */
+
+void quit (void)
+{
+ PRINTOUT ("bye\n");
+ exit (0);
+}
+
+/* help message */
+
+void help (void)
+{
+ PRINTOUT ("calc is a simple calculator\n\n");
+ PRINTOUT ("supported operators:\n");
+ PRINTOUT (" + - * / % ^\n\n");
+ PRINTOUT ("supported functions:\n");
+ PRINTOUT (" pow sqrt cos sin atan log exp\n\n");
+ PRINTOUT ("miscellaneous functions:\n");
+ PRINTOUT (" quit help\n");
+}
+
+/* evaluate element tree */
+
+#define MASK_SUB 0x1
+#define MASK_DIV 0x2
+
+double evaluate_element (element_t *root, char mask)
+{
+ double op0 = 0, op1 = 0;
+ char nextmask = mask;
+
+ if ((root == NULL) || (root == ERROR_OP)) {
+ VERBOSE (WARNING, PRINTOUT ("error while evaluating\n"));
+ return 0;
+ }
+
+ /* mask to manage sub operator sub and div */
+ switch (root->func) {
+ case Add:
+ nextmask &= ~MASK_SUB;
+ nextmask &= ~MASK_DIV;
+ break;
+ case Sub:
+ nextmask |= MASK_SUB;
+ nextmask &= ~MASK_DIV;
+ break;
+ case Mul:
+ nextmask &= ~MASK_DIV;
+ break;
+ case Div:
+ nextmask |= MASK_DIV;
+ break;
+ default:
+ nextmask = mask;
+ }
+
+ switch (root->func) {
+ case Val:
+ case Sig:
+ op0 = (root->ops[0]) ? evaluate_element (root->ops[0], nextmask) : root->value;
+ break;
+ case Add:
+ case Sub:
+ case Mul:
+ case Div:
+ case Mod:
+ case Pow:
+ if (root->ops[1]) {
+ op1 = evaluate_element (root->ops[1], nextmask);
+ } else {
+ VERBOSE (WARNING, PRINTOUT ("error while evaluating (op[1])\n"));
+ return 0;
+ }
+ /* fallthrough */
+ case Sqr:
+ case Cos:
+ case Sin:
+ case Atn:
+ case Log:
+ case Exp:
+ if (root->ops[0]) {
+ op0 = evaluate_element (root->ops[0], 0);
+ } else {
+ VERBOSE (WARNING, PRINTOUT ("error while evaluating (op[0])\n"));
+ return 0;
+ }
+ break;
+ case Qui:
+ case Hel:
+ break;
+ }
+
+ switch (root->func) {
+ case Val: return op0;
+ case Sig: return -op0;
+ case Add: return ((mask & MASK_SUB) == 0) ? op0 + op1 : op0 - op1;
+ case Sub: return ((mask & MASK_SUB) == 0) ? op0 - op1 : op0 + op1;
+ case Mul: return ((mask & MASK_DIV) == 0) ? op0 * op1 : op0 / op1;
+ case Div: return ((mask & MASK_DIV) == 0) ? op0 / op1 : op0 * op1;
+ case Mod: return fmod (op0, op1);
+ case Pow: return pow (op0, op1);
+ case Sqr: return sqrt (op0);
+ case Cos: return cos (op0);
+ case Sin: return sin (op0);
+ case Atn: return atan (op0);
+ case Log: return log (op0);
+ case Exp: return exp (op0);
+ case Qui: quit (); break;
+ case Hel: help (); break;
+ }
+
+ return 0;
+}
+