From 51c8325661eab4667a11431175f12eb6a08cc36a Mon Sep 17 00:00:00 2001
From: Frederick Yin <fkfd@fkfd.me>
Date: Mon, 22 Aug 2022 17:24:46 +0800
Subject: hack-vm: branching

---
 projects/hack-vm/__main__.py  |  3 +++
 projects/hack-vm/branching.py | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 projects/hack-vm/branching.py

diff --git a/projects/hack-vm/__main__.py b/projects/hack-vm/__main__.py
index a1dce1f..5373fe9 100644
--- a/projects/hack-vm/__main__.py
+++ b/projects/hack-vm/__main__.py
@@ -2,6 +2,7 @@ from argparse import ArgumentParser
 from .memory import translate_memory
 from .arith_logic import translate_arith_logic
 from .compare import translate_compare
+from .branching import translate_branching
 from .utils import *
 
 
@@ -38,6 +39,8 @@ def vm_translate(input_path):
                 asm += translate_arith_logic(command)
             case [("lt" | "eq" | "gt") as command]:
                 asm += translate_compare(command)
+            case [("label" | "goto" | "if-goto") as action, label]:
+                asm += translate_branching(action, label)
             case _:
                 exit_on_error(
                     f"Syntax error: invalid command: {cmd}", EXIT_CODE_SYNTAX_ERROR
diff --git a/projects/hack-vm/branching.py b/projects/hack-vm/branching.py
new file mode 100644
index 0000000..b73ed94
--- /dev/null
+++ b/projects/hack-vm/branching.py
@@ -0,0 +1,24 @@
+from .utils import *
+
+LABEL_ASM = "({label})\n"
+
+GOTO_ASM = """@{label}
+0;JMP
+"""
+
+IF_GOTO_ASM = """@SP
+AM=M-1
+D=M
+@{label}
+D;JNE
+"""
+
+BRANCHING_ASM = {
+    "label": LABEL_ASM,
+    "goto": GOTO_ASM,
+    "if-goto": IF_GOTO_ASM,
+}
+
+
+def translate_branching(action, label):
+    return BRANCHING_ASM[action].format(label=label)
-- 
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