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authorFrederick Yin <fkfd@fkfd.me>2022-08-22 17:04:19 +0800
committerFrederick Yin <fkfd@fkfd.me>2022-08-22 17:04:19 +0800
commit10c9f64f592198d78aad11ebc676629d92ca6576 (patch)
tree1b4f8a21c72dae1700d92892a619ad9ddaf25cbf /projects/hack-vm/memory.py
parent900bd8fe1934f83ea35ab8673dda5239ae2dfca8 (diff)
Project 07: VM translator part 1
Diffstat (limited to 'projects/hack-vm/memory.py')
-rw-r--r--projects/hack-vm/memory.py129
1 files changed, 129 insertions, 0 deletions
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
+ )