From 10c9f64f592198d78aad11ebc676629d92ca6576 Mon Sep 17 00:00:00 2001
From: Frederick Yin <fkfd@fkfd.me>
Date: Mon, 22 Aug 2022 17:04:19 +0800
Subject: Project 07: VM translator part 1

---
 projects/hack-vm/memory.py | 129 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 129 insertions(+)
 create mode 100644 projects/hack-vm/memory.py

(limited to 'projects/hack-vm/memory.py')

diff --git a/projects/hack-vm/memory.py b/projects/hack-vm/memory.py
new file mode 100644
index 0000000..ad22482
--- /dev/null
+++ b/projects/hack-vm/memory.py
@@ -0,0 +1,129 @@
+from .utils import *
+
+# common instructions all push commands end with
+PUSH_COMMON_ASM = """@SP
+A=M
+M=D
+@SP
+M=M+1
+"""
+
+# push <segment> <index>
+# when <segment> is one of local, argument, this and that
+PUSH_ASM = (
+    """@{segment}
+D=M
+@{index}
+A=D+A
+D=M
+"""
+    + PUSH_COMMON_ASM
+)
+
+# when <segment> is one of static, temp and pointer
+PUSH_FIXED_ASM = (
+    """@{addr}
+D=M
+"""
+    + PUSH_COMMON_ASM
+)
+
+# push constant <constant>
+PUSH_CONSTANT_ASM = (
+    """@{constant}
+D=A
+"""
+    + PUSH_COMMON_ASM
+)
+
+
+# pop <segment> <index>
+# when <segment> is one of local, argument, this and that
+POP_ASM = """@{index}
+D=A
+@{segment}
+M=M+D
+@SP
+M=M-1
+A=M
+D=M
+@{segment}
+A=M
+M=D
+@{index}
+D=A
+@{segment}
+M=M-D
+"""
+
+# when <segment> is one of static, temp and pointer
+POP_FIXED_ASM = """@SP
+M=M-1
+A=M
+D=M
+@{addr}
+M=D
+"""
+
+SEGMENT_PTR = {
+    "local": "LCL",
+    "argument": "ARG",
+    "this": "THIS",
+    "that": "THAT",
+}
+
+SEGMENT_SIZE = {
+    "pointer": 2,  # 3..4, i.e. THIS and THAT
+    "temp": 8,  # 5..12
+    "static": 240,  # 16..255
+}
+
+
+def translate_memory(action, segment, index, prog):
+    try:
+        index = int(index)
+    except ValueError:
+        exit_on_error(
+            f"Syntax error: invalid segment index {index}", EXIT_CODE_SYNTAX_ERROR
+        )
+
+    if index < 0:
+        exit_on_error(
+            f"Address error: negative segment index {index}", EXIT_CODE_ADDR_ERROR
+        )
+
+    asm = ""
+    if segment in ["local", "argument", "this", "that"]:
+        # these segments are dynamic
+        asm = PUSH_ASM if action == "push" else POP_ASM
+        return asm.format(segment=SEGMENT_PTR[segment], index=index)
+    elif segment in ["static", "temp", "pointer"]:
+        # these segments have a fixed location and size on memory
+        if index >= SEGMENT_SIZE[segment]:
+            exit_on_error(
+                f"Address error: segment index {index} exceeds size of {segment}",
+                EXIT_CODE_ADDR_ERROR,
+            )
+
+        addr = ""
+        if segment == "static":
+            # translate "static i" in "prog.vm" into "@prog.i"
+            addr = f"{prog}.{index}"
+        elif segment == "temp":
+            addr = str(5 + index)
+        else:
+            # "pointer 0" is THIS, "pointer 1" is THAT
+            addr = "THIS" if index == 0 else "THAT"
+
+        asm = PUSH_FIXED_ASM if action == "push" else POP_FIXED_ASM
+        return asm.format(addr=addr)
+    elif segment == "constant":
+        if action == "pop":
+            exit_on_error(
+                f"Syntax error: popping to constant not allowed", EXIT_CODE_SYNTAX_ERROR
+            )
+        return PUSH_CONSTANT_ASM.format(constant=index)
+    else:
+        exit_on_error(
+            f"Syntax error: invalid memory segment {segment}", EXIT_CODE_SYNTAX_ERROR
+        )
-- 
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