1 files changed, 153 insertions, 0 deletions
diff --git a/src/user/app/kbasic/expr.c b/src/user/app/kbasic/expr.c
new file mode 100644
index 0000000..3b8d558
--- /dev/null
+++ b/src/user/app/kbasic/expr.c
@@ -0,0 +1,153 @@
+#include <stdlib.h>
+
+#include "basic.h"
+
+void level2(int*), level3(int*), level4(int*), level5(int*), level6(int*), primitive(int*);
+void unary(char, int*), arith(char, int*, int*);
+
+/* Entry point into parser. */
+void get_exp(int *result)
+{
+	get_token();
+	if(!*token) {
+		serror(2);
+		return;
+	}
+	level2(result);
+	putback(); /* return last token read to input stream */
+}
+
+/*  Add or subtract two terms. */
+void level2(int *result)
+{
+	register char  op; 
+	int hold; 
+
+	level3(result); 
+	while((op = *token) == '+' || op == '-') {
+		get_token(); 
+		level3(&hold); 
+		arith(op, result, &hold);
+	}
+}
+
+/* Multiply or divide two factors. */
+void level3(int *result)
+{
+	register char  op; 
+	int hold;
+
+	level4(result); 
+	while((op = *token) == '*' || op == '/' || op == '%') {
+		get_token(); 
+		level4(&hold); 
+		arith(op, result, &hold); 
+	}
+}
+
+/* Process integer exponent. */
+void level4(int *result)
+{
+	int hold; 
+
+	level5(result); 
+	if(*token== '^') {
+		get_token(); 
+		level4(&hold); 
+		arith('^', result, &hold); 
+	}
+}
+
+/* Is a unary + or -. */
+void level5(int *result)
+{
+	register char  op; 
+
+	op = 0; 
+	if((token_type==DELIMITER) && (*token=='+' || *token=='-')) {
+		op = *token; 
+		get_token(); 
+	}
+	level6(result); 
+	if(op)
+		unary(op, result); 
+}
+
+/* Process parenthesized expression. */
+void level6(int *result)
+{
+	if((*token == '(') && (token_type == DELIMITER)) {
+		get_token(); 
+		level2(result); 
+		if(*token != ')')
+			serror(1);
+		get_token(); 
+	}
+	else
+		primitive(result);
+}
+
+/* Find value of number or variable. */
+void primitive(int *result)
+{
+
+	switch(token_type) {
+		case VARIABLE:
+			*result = *find_var(token);
+			get_token(); 
+			return; 
+		case NUMBER:
+			*result = atoi(token);
+			get_token();
+			return;
+		case COMMAND:
+			switch(tok) {
+				case RND:
+					*result = rand();
+					get_token();
+					return;
+			}
+		default:
+			serror(0);
+	}
+}
+
+/* Perform the specified arithmetic. */
+void arith(char o, int *r, int *h)
+{
+	register int t, ex;
+
+	switch(o) {
+		case '-':
+			*r = *r-*h; 
+			break; 
+		case '+':
+			*r = *r+*h; 
+			break; 
+		case '*':  
+			*r = *r * *h; 
+			break; 
+		case '/':
+			*r = (*r)/(*h);
+			break; 
+		case '%':
+			t = (*r)/(*h); 
+			*r = *r-(t*(*h)); 
+			break; 
+		case '^':
+			ex = *r; 
+			if(*h==0) {
+				*r = 1; 
+				break; 
+			}
+			for(t=*h-1; t>0; --t) *r = (*r) * ex;
+			break;       
+	}
+}
+
+/* Reverse the sign. */
+void unary(char o, int *r)
+{
+	if(o=='-') *r = -(*r);
+}
+