M projects/06/assembler1/assembler1.c → projects/06/assembler1/assembler1.c

@@ -107,27 +107,78 @@ /* returns jump bits 0b00000jjj
  */
 static bool parse_c_type_jump(const char *jump_line, uint8_t *jump)
 {
-	// Note: can do 'jump' fields via lookup tables once extracted from line
+	size_t len;
+	char j0, j1, j2;
+	char *err_1st_char = "syntax error: jump field doesn't start with 'J'\n";
+	char *err_2nd_char = "syntax error: 2nd letter in jump field incorrect\n";
+	char *err_3rd_char = "syntax error: 3rd letter in jump field incorrect\n";
+
 	DEBUG("jump_line: %s\n", jump_line);
-	
-	/* if 'J'
-	 *     if 'G'
-	 *         if 'T'
-	 *         if 'E'
-	 *     if 'E'
-	 *         if 'Q'
-	 *     if 'L'
-	 *         if 'T'
-	 *         if 'E'
-	 *     if 'N'
-	 *         if 'E'
-	 *     if 'M'
-	 *         if 'P'
-	 * default:
-	 *     "syntax error"
-	 */
+
+	for (len = 0; jump_line[len] == 'J' || jump_line[len] == 'G' ||
+	              jump_line[len] == 'T' || jump_line[len] == 'E' ||
+	              jump_line[len] == 'Q' || jump_line[len] == 'L' ||
+	              jump_line[len] == 'N' || jump_line[len] == 'M' ||
+	              jump_line[len] == 'P'; ++len) {}
+	if (len != 3) {
+		alert("syntax error: jump field incorrect length %lu\n", len);
+		return false;
+	}
+
+	j0 = jump_line[0];
+	j1 = jump_line[1];
+	j2 = jump_line[2];
+
+	if (j0 == 'J') {                         // if "J__"
+		switch (j1) {
+		case 'G':                        // if "JG_"
+			if (j2 == 'T') {         // if "JGT"
+				*jump = 0x1;
+			} else if (j2 == 'E') {  // if "JGE"
+				*jump = 0x3;
+			} else {
+				alert(err_3rd_char); return false;
+			}
+			break;
+		case 'E':                        // if "JE_"
+			if (j2 == 'Q') {         // if "JEQ"
+				*jump = 0x2;
+			} else {
+				alert(err_3rd_char); return false;
+			}
+			break;
+		case 'L':                        // if "JL_"
+			if (j2 == 'T') {         // if "JLT"
+				*jump = 0x4;
+			} else if (j2 == 'E') {  // if "JLE"
+				*jump = 0x6;
+			} else {
+				alert(err_3rd_char); return false;
+			}
+			break;
+		case 'N':                        // if "JN_"
+			if (j2 == 'E') {         // if "JNE"
+				*jump = 0x5;
+			} else {
+				alert(err_3rd_char); return false;
+			}
+			break;
+		case 'M':                        // if "JM_"
+			if (j2 == 'P') {         // if "JMP"
+				*jump = 0x7;
+			} else {
+				alert(err_3rd_char); return false;
+			}
+			break;
+		default:
+			alert(err_2nd_char);
+			return false;
+		}
+	} else {
+		alert(err_1st_char);
+		return false;
+	}
 
-	*jump = 0x01;  // 0b00000001
 	return true;
 }
 
@@ -142,9 +193,9 @@ char *dest_start = NULL;
 	char *comp_start = NULL;
 	char *jump_start = NULL;
 	size_t i = 0;
-	uint8_t dest = 0;
+	uint8_t dest = 0;  // default value when not present
 	uint8_t comp = 0;
-	uint8_t jump = 0;
+	uint8_t jump = 0;  // default value when not present
 
 	c = line[0];
 	for (i = 0; c != ' ' && c != '\t' &&
@@ -154,6 +205,7 @@ 
 		if (c == '=') {
 			if (1 <= i && i <= 3) {
 				dest_start = &line[0];   // start of line
+				// this 'i+1' might be dangerous!
 				comp_start = &line[i+1]; // after "[dest]="
 			} else {
 				//syntax error
@@ -163,6 +215,7 @@ return false;
 			}
 		} else if (c == ';') {
 			if (1 <= i && i <= 7) {
+				// this 'i+1' might be dangerous!
 				jump_start = &line[i+1]; // after "[comp];"
 			} else {
 				//syntax error