projects/07/src/codewriter.h
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#ifndef _CODEWRITER_H
#define _CODEWRITER_H
// 'codewriter.h' roughly corresponds to the 'CodeWriter' module specified in
// nand2tetris, with a few liberties taken.
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "parser.h"
#include "util.h"
#define _DEBUG
// memory mapping:
// 0-15 virtual registers R0-R15
// 16-255 static variables
// 256-2047 stack
#define SP (0) // points to stack
#define LCL (1) // points to local segment
#define ARG (2) // points to argument segment
#define POINTER (3)
#define THIS (3) //
#define THAT (4) //
#define TEMP (5) //
#define R13 (13) // R13-R15 are scratch space that
#define R14 (14) // VM-generated assembly can use
#define R15 (15) // for whatever.
#define STATIC (16) // start of static variables segment (240 words long)
char vm_init[] = "@256\n" // starting address of stack
"D=A\n" // D = 256
"@SP\n" // A = <constant representing address of SP>
"M=D\n" // <memory pointed to by SP> = 256
"\n";
// TODO: add initializers for argument, local, static, constant, this, that
// static segment index indexes into map, retrieves hack assembly symbol offset
#define MAX_STATIC_SYMBOLS (240) // for whatever.
uint16_t static_symbol_map[MAX_STATIC_SYMBOLS];
uint8_t g_symbol_offset_bump = 0; // holds current largest symbol offset, bumps
void write_vm_init(FILE *fp)
{
//fprintf(fp, vm_init);
fprintf(fp, "// TODO eventually output VM initialization assembly\n");
}
static bool write_arithmetic(struct vm_instruction_t *vm_instr, FILE *fp)
{
// TODO: write assembly code for 'add' and 'neg' instructions, turn into
// codegen
fprintf(fp, "ARITHMETIC INSTRUCTION: ");
print_vm_instruction(vm_instr);
return true;
}
static bool resolve_static_address(struct vm_instruction_t *vm_instr,
uint16_t *addr)
{
uint16_t symbol_offset;
if (vm_instr->arg2 >= MAX_STATIC_SYMBOLS) {
err("error: arg2 too large, >= %u\n", MAX_STATIC_SYMBOLS);
return false;
}
symbol_offset = static_symbol_map[vm_instr->arg2];
if (symbol_offset == 0xffff) { // new offset not in map (-1 special)
if (g_symbol_offset_bump >= MAX_STATIC_SYMBOLS) {
err("error: symbol offset grew too large (>= %u), "
"too many static variables\n", MAX_STATIC_SYMBOLS);
return false;
}
static_symbol_map[vm_instr->arg2] = g_symbol_offset_bump;
*addr = STATIC + g_symbol_offset_bump;
++g_symbol_offset_bump; // bump global symbol offset
} else {
// offset was found in map, return symbol value/index
*addr = STATIC + symbol_offset;
}
return true;
}
// returns addr
static bool resolve_segment_offset(struct vm_instruction_t *vm_instr,
uint16_t *addr)
{
// TODO implement
// resolve base (address) of segment
// check index is valid for that segment
// add index vm_instr->arg2 to address
// set to *addr
return true;
}
// push 16-bit value from segment offset onto top of stack
static bool write_push(struct vm_instruction_t *vm_instr, FILE *fp)
{
uint16_t addr, arg2 = vm_instr->arg2;
// TODO: maybe add SP counter/check to catch overflows
// TODO: if vm_instr->arg1 == "constant", push_constant, else push_segment
char push_const_boilerplate[] = "@%hu\n" // A = constant
"D=A\n" // D = constant
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M\n" // A = RAM[SP]
"M=D\n"; // RAM[SP] = constant
char push_addr_boilerplate[] = "@%hu\n" // A = segment + index
"D=M\n" // D = RAM[segment + index]
"@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M\n" // A = RAM[SP]
"M=D\n"; // RAM[SP] = constant
char push_indirect_boilerplate[] = "@%hu\n" // A = segment
"D=A\n" // D = segment
"@%hu\n" // A = index
"A=A+D\n" // A = segment + index
"D=M\n" // D = RAM[segment + index]
"@SP\n"
"M=M+1\n" // RAM[SP]++
"A=M\n" // A = RAM[SP]
"M=D\n";
if (!strcmp(vm_instr->arg1, "constant")) {
// TODO: check size of constant (allowed to be > 32,767?)
// TODO: look up in nand2tetris forums in case issue already noted
fprintf(fp, push_const_boilerplate, arg2);
} else {
// TODO: move segment resolution to separate function
if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, push_indirect_boilerplate, ARG, arg2);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, push_indirect_boilerplate, LCL, arg2);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, push_addr_boilerplate, addr);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, push_indirect_boilerplate, THIS, arg2);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, push_indirect_boilerplate, THAT, arg2);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, push_addr_boilerplate, addr);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, push_addr_boilerplate, addr);
} else {
err("error: invalid segment name \"%s\"\n",
vm_instr->arg1);
return false;
}
}
return true;
}
// pop 16-bit value from top of stack into segment offset
static bool write_pop(struct vm_instruction_t *vm_instr, FILE *fp)
{
// TODO: maybe add SP counter/check to catch overflows
// can use R13-R15 for scratch space
uint16_t addr, arg2 = vm_instr->arg2;
char pop_addr_boilerplate[] = "@%hu\n" // A = segment + index
"D=M\n" // D = RAM[segment + index]
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"M=D\n"; // D = RAM[SP]
char pop_indirect_boilerplate[] = "@%hu\n" // @segment
"D=A\n" // D = segment
"@%hu\n" // @index
"A=A+D\n" // A = segment + index
"D=M\n" // D = RAM[segment + index]
"@SP\n"
"AM=M-1\n" // RAM[SP]--; A = RAM[SP]
"M=D\n";
// TODO: move segment resolution to separate function
if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, pop_indirect_boilerplate, ARG, arg2);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, pop_indirect_boilerplate, LCL, arg2);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, pop_addr_boilerplate, addr);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, pop_indirect_boilerplate, THIS, arg2);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, pop_indirect_boilerplate, THAT, arg2);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, pop_addr_boilerplate, addr);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, pop_addr_boilerplate, addr);
} else {
err("error: invalid segment name \"%s\"\n",
vm_instr->arg1);
return false;
}
return true;
}
bool write_instruction(struct vm_instruction_t *vm_instr, FILE *fp)
{
fprintf(fp, "\n// %lu: %s\n", file_line_no, vm_instr->line);
if (vm_instr->cmd == C_ARITHMETIC) {
write_arithmetic(vm_instr, fp);
} else if (vm_instr->cmd == C_PUSH) {
write_push(vm_instr, fp);
} else if (vm_instr->cmd == C_POP) {
write_pop(vm_instr, fp);
} else {
// TODO: eventually error if unrecognized instruction
print_vm_instruction(vm_instr);
}
return true;
}
#endif // _CODEWRITER_H
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