Execute Brain****: Difference between revisions

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@@ Line 3,578: / Line 3,578: @@
 [[/Java|Implementation in Java]].
+import java.io.IOException;
+public class Interpreter {
+    public final static int MEMORY_SIZE = 65536;
+    private final char[] memory = new char[MEMORY_SIZE];
+    private int dp;
+    private int ip;
+    private int border;
+    private void reset() {
+        for (int i = 0; i < MEMORY_SIZE; i++) {
+            memory[i] = 0;
+        }
+        ip = 0;
+        dp = 0;
+    }
+    private void load(String program) {
+        if (program.length() > MEMORY_SIZE - 2) {
+            throw new RuntimeException("Not enough memory.");
+        }
+        reset();
+        for (; dp < program.length(); dp++) {
+            memory[dp] = program.charAt(dp);
+        }
+        // memory[border] = 0 marks the end of instructions. dp (data pointer) cannot move lower than the
+        // border into the program area.
+        border = dp;
+        dp += 1;
+    }
+    public void execute(String program) {
+        load(program);
+        char instruction = memory[ip];
+        while (instruction != 0) {
+            switch (instruction) {
+                case '>':
+                    dp++;
+                    if (dp == MEMORY_SIZE) {
+                        throw new RuntimeException("Out of memory.");
+                    }
+                    break;
+                case '<':
+                    dp--;
+                    if (dp == border) {
+                        throw new RuntimeException("Invalid data pointer.");
+                    }
+                    break;
+                case '+':
+                    memory[dp]++;
+                    break;
+                case '-':
+                    memory[dp]--;
+                    break;
+                case '.':
+                    System.out.print(memory[dp]);
+                    break;
+                case ',':
+                    try {
+                        // Only works for one byte characters.
+                        memory[dp] = (char) System.in.read();
+                    } catch (IOException e) {
+                        throw new RuntimeException(e);
+                    }
+                    break;
+                case '[':
+                    if (memory[dp] == 0) {
+                        skipLoop();
+                    }
+                    break;
+                case ']':
+                    if (memory[dp] != 0) {
+                        loop();
+                    }
+                    break;
+                default:
+                    throw new RuntimeException("Unknown instruction.");
+            }
+            instruction = memory[++ip];
+        }
+    }
+    private void skipLoop() {
+        int loopCount = 0;
+        while (memory[ip] != 0) {
+            if (memory[ip] == '[') {
+                loopCount++;
+            } else if (memory[ip] == ']') {
+                loopCount--;
+                if (loopCount == 0) {
+                    return;
+                }
+            }
+            ip++;
+        }
+        if (memory[ip] == 0) {
+            throw new RuntimeException("Unable to find a matching ']'.");
+        }
+    }
+    private void loop() {
+        int loopCount = 0;
+        while (ip >= 0) {
+            if (memory[ip] == ']') {
+                loopCount++;
+            } else if (memory[ip] == '[') {
+                loopCount--;
+                if (loopCount == 0) {
+                    return;
+                }
+            }
+            ip--;
+        }
+        if (ip == -1) {
+            throw new RuntimeException("Unable to find a matching '['.");
+        }
+    }
+    public static void main(String[] args) {
+        Interpreter interpreter = new Interpreter();
+        interpreter.execute(">++++++++[-<+++++++++>]<.>>+>-[+]++>++>+++[>[->+++<<+++>]<<]>-----.>->+++..+++.>-.<<+[>[+>+]>>]<--------------.>>.+++.------.--------.>+.>+.");
+    }
+}
 =={{header|JavaScript}}==