projects/08/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 word ahead of top of 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, 16-255)
char *static_sym_name;
// 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
char comp_vm_funcs[] = "@__comp_funcs_end\n"
"0;JMP\n"
"\n"
"(__test_eq)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if D == 0, equal
"M=0\n" // prematurely push false
"@__test_eq_neq\n" // if D == 0, equal
"D;JNE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_eq_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__test_gt)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if (D - M) > 0; push true
"M=0\n" // prematurely push false
"@__test_gt_neq\n" // if D == 0, equal
"D;JLE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_gt_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__test_lt)\n"
"@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"D=M-D\n" // if (D - M) < 0; push true
"M=0\n" // prematurely push false
"@__test_lt_neq\n" // if D == 0, equal
"D;JGE\n" // if D != 0, not equal, jump
"@SP\n" // get SP
"A=M-1\n" // get bottom stack val address
"M=-1\n" // push 0xffff (true)
"(__test_lt_neq)\n"
"@R13\n" // return address in RAM[R13]
"A=M\n" // A = return address
"0;JMP\n" // return
"\n"
"(__comp_funcs_end)\n";
char vm_init[] = "//@256\n" // starting address of stack (nothing pushed yet)
"//D=A\n" // D = 256
"//@SP\n" // A = <constant representing address of SP>
"//M=D\n" // <memory pointed to by SP> = 256
"\n%s\n"; // <- comp_vm_funcs
// TODO: add initializers for argument, local, static, constant, this, that
char vm_stop[] = "(END)\n" // starting address of stack (nothing pushed yet)
"@END\n" // D = 256
"0;JMP\n"; // A = <constant representing address of SP>
void write_vm_init(FILE *fp)
{
fprintf(fp, vm_init, comp_vm_funcs);
}
void write_vm_stop(FILE *fp)
{
fprintf(fp, "\n%s", vm_stop);
}
static bool write_arithmetic(struct vm_instruction_t *vm_instr, FILE *fp)
{
char binary_op_template[] = "@SP\n"
"AM=M-1\n" // RAM[SP]--, A = RAM[SP]
"D=M\n" // D = RAM[SP] (top stack val)
"A=A-1\n" // --A (--> bottom stack val)
"%s"; // arithmetic op goes here
char unary_op_template[] = "@SP\n"
"A=M-1\n" // A = SP - 1
"%s"; // arithmetic op goes here
char op_add[] = "M=D+M\n";
char op_sub[] = "M=M-D\n";
char op_eq[] = "@%s_%lu_eq\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_eq\n"
"0;JMP\n"
"(%s_%lu_eq)\n" // return here
"\n";
char op_gt[] = "@%s_%lu_gt\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_gt\n"
"0;JMP\n"
"(%s_%lu_gt)\n" // return here
"\n";
char op_lt[] = "@%s_%lu_lt\n" // <- static_sym_name, file_line_number
"D=A\n"
"@R13\n"
"M=D\n"
"@__test_lt\n"
"0;JMP\n"
"(%s_%lu_lt)\n" // return here
"\n";
char op_and[] = "M=D&M\n";
char op_or[] = "M=D|M\n";
char op_neg[] = "M=-M\n";
char op_not[] = "M=!M\n";
// binary operations
if (!strncmp(vm_instr->arg1, "add", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_add);
} else if (!strncmp(vm_instr->arg1, "sub", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_sub);
} else if (!strncmp(vm_instr->arg1, "eq", CMD_STR_MAX_LEN)) {
fprintf(fp, op_eq, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "gt", CMD_STR_MAX_LEN)) {
fprintf(fp, op_gt, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "lt", CMD_STR_MAX_LEN)) {
fprintf(fp, op_lt, static_sym_name, file_line_no,
static_sym_name, file_line_no);
} else if (!strncmp(vm_instr->arg1, "and", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_and);
} else if (!strncmp(vm_instr->arg1, "or", CMD_STR_MAX_LEN)) {
fprintf(fp, binary_op_template, op_or);
// unary operations
} else if (!strncmp(vm_instr->arg1, "neg", CMD_STR_MAX_LEN)) {
fprintf(fp, unary_op_template, op_neg);
} else if (!strncmp(vm_instr->arg1, "not", CMD_STR_MAX_LEN)) {
fprintf(fp, unary_op_template, op_not);
} else {
err("error: invalid arithmetic op \"%s\"\n", vm_instr->arg1);
return false;
}
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 = g_symbol_offset_bump;
++g_symbol_offset_bump; // bump global symbol offset
} else {
// offset found in map, return symbol value/index
*addr = symbol_offset;
}
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: could add SP counter/check to catch overflows
char const_template[] = "@%hu\n" // A = constant
"D=A\n%s"; // D = constant
char addr_template[] = "@%hu\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char static_template[] = "@%s.%hu\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char indirect_template[] = "@%hu\n" // A = segment
"D=M\n" // D = RAM[segment]
"@%hu\n" // A = index
"A=A+D\n" // A = segment + index
"D=M\n%s"; // D = RAM[segment + index]
char push_boilerplate[] = "@SP\n"
"M=M+1\n" // RAM[SP]++ // inc SP
"A=M-1\n" // A = RAM[SP] - 1 // prev top
"M=D\n"; // RAM[SP] = constant
if (!strcmp(vm_instr->arg1, "constant")) {
// TODO: check size of constant (allowed to be > 32,767?)
// TODO: look in nand2tetris forums in case issue already noted
fprintf(fp, const_template, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, indirect_template, ARG, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, indirect_template, LCL, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, static_template, static_sym_name, addr,
push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, indirect_template, THIS, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, indirect_template, THAT, arg2, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, addr_template, addr, push_boilerplate);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, addr_template, addr, push_boilerplate);
} 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: could add SP counter/check to catch overflows
uint16_t addr, arg2 = vm_instr->arg2;
char pop_indirect_template[] = "@%hu\n" // @segment
"D=M\n" // D = segment
"@%hu\n" // @index
"D=A+D\n" // A = segment + index
"@R13\n"
"M=D\n" // RAM[13] = segment + index
"@SP\n" //
"AM=M-1\n" //
"D=M\n" //
"@R13\n" //
"A=M\n" //
"M=D\n"; //
char pop_addr_template[] = "@SP\n"
"AM=M-1\n" // decrement SP
"D=M\n" // "pop" (read) value into D
"@%hu\n" // load address
"M=D\n"; // "pop" (write) value to RAM
char pop_static_template[] = "@SP\n"
"AM=M-1\n" // decrement SP
"D=M\n" // "pop" (read) value into D
"@%s.%hu\n" // A = segment + index
"M=D\n"; // RAM[segment + index] = D
if (!strcmp(vm_instr->arg1, "argument")) {
fprintf(fp, pop_indirect_template, ARG, arg2);
} else if (!strcmp(vm_instr->arg1, "local")) {
fprintf(fp, pop_indirect_template, LCL, arg2);
} else if (!strcmp(vm_instr->arg1, "static")) {
if (!resolve_static_address(vm_instr, &addr)) {
return false;
}
fprintf(fp, pop_static_template, static_sym_name, addr);
} else if (!strcmp(vm_instr->arg1, "this")) {
fprintf(fp, pop_indirect_template, THIS, arg2);
} else if (!strcmp(vm_instr->arg1, "that")) {
fprintf(fp, pop_indirect_template, THAT, arg2);
} else if (!strcmp(vm_instr->arg1, "pointer")) {
addr = POINTER + vm_instr->arg2;
fprintf(fp, pop_addr_template, addr);
} else if (!strcmp(vm_instr->arg1, "temp")) {
addr = TEMP + vm_instr->arg2;
fprintf(fp, pop_addr_template, 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 {
err("error: unrecognized instruction (%u)\n", vm_instr->cmd);
return false;
}
return true;
}
#endif // _CODEWRITER_H
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