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#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#define MAX_ASM_LINE_LEN 64
#define INST_CHUNK_LEN 64
#define MAX_INST_LEN 32768
#define MAX_ADDR 32767
struct symbol {
char *label;
int addr;
};
void write_binary(FILE *file, uint16_t *binary, int cnt) {
for (int i = 0; i < cnt; i++) {
char binary_str[17];
binary_str[16] = '\0';
for (int b = 0; b < 16; b++) {
binary_str[b] = '0' + (*(binary + i) >> (15 - b)) % 2;
}
fprintf(file, "%s\n", binary_str);
}
}
uint16_t assemble_inst(char *asm_line) {
// assemble one line of assembly, terminated with \0
// labels and variables must be replaced with corresponding addresses beforehand
if (*asm_line == '@') {
// A instruction
return atoi(asm_line + 1);
} else {
// C instruction
uint16_t inst = 0xe000; // set 3 MSBs to 1
char *eq = asm_line;
for (char *c = asm_line; *c != '\0'; c++) {
// find first equal sign (eq == asm_line if not found)
if (*c == '=') {
eq = c;
break;
}
}
// slice out destination and copy to dest
int dest_len = eq - asm_line;
char *dest = malloc(dest_len + 1);
strncpy(dest, asm_line, dest_len);
dest[dest_len] = '\0';
if (dest_len == 0) {} // ignore
else if (strcmp(dest, "M") == 0) inst |= 0b001 << 3;
else if (strcmp(dest, "D") == 0) inst |= 0b010 << 3;
else if (strcmp(dest, "MD") == 0) inst |= 0b011 << 3;
else if (strcmp(dest, "A") == 0) inst |= 0b100 << 3;
else if (strcmp(dest, "AM") == 0) inst |= 0b101 << 3;
else if (strcmp(dest, "AD") == 0) inst |= 0b110 << 3;
else if (strcmp(dest, "AMD") == 0) inst |= 0b111 << 3;
free(dest);
char *semi = eq;
for (; *semi != '\0'; semi++) {
// find jump instruction after semicolon (;) (*semi == '\0' if not found)
if (*semi == ';') break;
}
// ignore if there's no semicolon, or there's nothing after it
if (*semi == '\0' || *(semi + 1) == '\0') {}
else if (strcmp(semi + 1, "JGT") == 0) inst |= 0b001;
else if (strcmp(semi + 1, "JEQ") == 0) inst |= 0b010;
else if (strcmp(semi + 1, "JGE") == 0) inst |= 0b011;
else if (strcmp(semi + 1, "JLT") == 0) inst |= 0b100;
else if (strcmp(semi + 1, "JNE") == 0) inst |= 0b101;
else if (strcmp(semi + 1, "JLE") == 0) inst |= 0b110;
else if (strcmp(semi + 1, "JMP") == 0) inst |= 0b111;
// slice out computation and copy to comp
int comp_len = (*eq == '=') ? (semi - eq - 1) : (semi - eq);
char *comp = malloc(comp_len + 1);
strncpy(comp, (*eq == '=') ? (eq + 1) : eq, comp_len);
comp[comp_len] = '\0';
if (strcmp(comp, "0") == 0) inst |= 0b0101010 << 6;
else if (strcmp(comp, "1") == 0) inst |= 0b0111111 << 6;
else if (strcmp(comp, "-1") == 0) inst |= 0b0111010 << 6;
else if (strcmp(comp, "D") == 0) inst |= 0b0001100 << 6;
else if (strcmp(comp, "A") == 0) inst |= 0b0110000 << 6;
else if (strcmp(comp, "M") == 0) inst |= 0b1110000 << 6;
else if (strcmp(comp, "!D") == 0) inst |= 0b0001101 << 6;
else if (strcmp(comp, "!A") == 0) inst |= 0b0110001 << 6;
else if (strcmp(comp, "!M") == 0) inst |= 0b1110001 << 6;
else if (strcmp(comp, "-D") == 0) inst |= 0b0001111 << 6;
else if (strcmp(comp, "-A") == 0) inst |= 0b0110011 << 6;
else if (strcmp(comp, "-M") == 0) inst |= 0b1110011 << 6;
else if (strcmp(comp, "D+1") == 0) inst |= 0b0011111 << 6;
else if (strcmp(comp, "A+1") == 0) inst |= 0b0110111 << 6;
else if (strcmp(comp, "M+1") == 0) inst |= 0b1110111 << 6;
else if (strcmp(comp, "D-1") == 0) inst |= 0b0001110 << 6;
else if (strcmp(comp, "A-1") == 0) inst |= 0b0110010 << 6;
else if (strcmp(comp, "M-1") == 0) inst |= 0b1110010 << 6;
else if (strcmp(comp, "D+A") == 0
|| strcmp(comp, "A+D") == 0) inst |= 0b0000010 << 6;
else if (strcmp(comp, "D+M") == 0
|| strcmp(comp, "M+D") == 0) inst |= 0b1000010 << 6;
else if (strcmp(comp, "D-A") == 0) inst |= 0b0010011 << 6;
else if (strcmp(comp, "D-M") == 0) inst |= 0b1010011 << 6;
else if (strcmp(comp, "A-D") == 0) inst |= 0b0000111 << 6;
else if (strcmp(comp, "M-D") == 0) inst |= 0b1000111 << 6;
else if (strcmp(comp, "D&A") == 0
|| strcmp(comp, "A&D") == 0) inst |= 0b0000000 << 6;
else if (strcmp(comp, "D&M") == 0
|| strcmp(comp, "M&D") == 0) inst |= 0b1000000 << 6;
else if (strcmp(comp, "D|A") == 0
|| strcmp(comp, "A|D") == 0) inst |= 0b0010101 << 6;
else if (strcmp(comp, "D|M") == 0
|| strcmp(comp, "M|D") == 0) inst |= 0b1010101 << 6;
free(comp);
return inst;
}
}
size_t assembler(char *input_fn) {
// open input file
FILE *input_file = fopen(input_fn, "r");
// find size of input file
fseek(input_file, 0, SEEK_END);
size_t file_size = ftell(input_file);
fseek(input_file, 0, SEEK_SET);
// read input file
char *file_content = malloc(file_size);
fread(file_content, file_size, 1, input_file);
fclose(input_file);
// strip away comments, labels, blank lines and whitespace from file_content
// resulting in lines of what looks like instructions in assembly but is not necessarily correct
// labels in parentheses are assigned corresponding addresses in ROM, then collected in `symbols`
// the strings are scattered in the heap but asm_lines collects pointers to them
char **asm_lines = calloc(INST_CHUNK_LEN, sizeof(char*));
int asm_line_cnt = 0; // no. of lines (metaphorically) written into asm_lines
char *asm_line = malloc(MAX_ASM_LINE_LEN + 1); // one line of (probably) assembly
int asm_char_cnt = 0; // no. of chars written into asm_line
struct symbol symbols[MAX_INST_LEN] = {
{"SP", 0}, {"LCL", 1}, {"ARG", 2}, {"THIS", 3}, {"THAT", 4},
{"R0", 0}, {"R1", 1}, {"R2", 2}, {"R3", 3},
{"R4", 4}, {"R5", 5}, {"R6", 6}, {"R7", 7},
{"R8", 8}, {"R9", 9}, {"R10", 10}, {"R11", 11},
{"R12", 12}, {"R13", 13}, {"R14", 14}, {"R15", 15},
{"SCREEN", 16384}, {"KBD", 24576},
};
const int predef_symbol_cnt = 23; // no. of predefined symbols
int user_symbol_cnt = 0;
for (size_t i = 0; i < file_size; i++) {
switch (file_content[i]) {
case '\n':
// end of line; try to figure out what's in asm_line
if (asm_char_cnt == 0) continue; // skip blank line or comment line
*(asm_line + asm_char_cnt) = '\0';
if (*asm_line == '(' && *(asm_line + asm_char_cnt - 1) == ')') {
// this line may be a label; extract label from between the parentheses
char *label = malloc(asm_char_cnt - 1);
strncpy(label, asm_line + 1, asm_char_cnt - 2);
free(asm_line);
*(label + asm_char_cnt - 2) = '\0';
symbols[predef_symbol_cnt + user_symbol_cnt] = (struct symbol) {label, asm_line_cnt};
user_symbol_cnt++;
} else {
// this line may be an instruction
// if we used up a chunk, realloc asm_lines
if (asm_line_cnt > 0 && asm_line_cnt % INST_CHUNK_LEN == 0) {
asm_lines = realloc(asm_lines, (asm_line_cnt + INST_CHUNK_LEN) * sizeof(char*));
}
asm_lines[asm_line_cnt] = asm_line;
asm_line_cnt++;
}
// allocate memory for next line
asm_char_cnt = 0;
asm_line = malloc(MAX_ASM_LINE_LEN + 1);
break;
case '/':
// we encountered a comment
// skip to last char of line
while (i + 1 < file_size && file_content[i + 1] != '\n') i++;
break;
case ' ':
case '\t':
case '\r':
break; // ignore whitespace and CR
default:
*(asm_line + asm_char_cnt) = file_content[i];
asm_char_cnt++;
}
}
free(asm_line);
free(file_content);
// find and assign address to variables on the fly
int addr = 16; // variable addresses start at 16
for (int i = 0; i < asm_line_cnt; i++) {
if (asm_lines[i] == NULL) break; // no more instructions
if (*(asm_lines[i]) != '@') continue; // not an A-instruction
char *addr_str = malloc(strlen(asm_lines[i]));
strcpy(addr_str, asm_lines[i] + 1); // whatever comes after the @
bool is_symbol = false;
for (char *c = addr_str; *c != '\0'; c++) {
// search for non-numeric chars in addr_str
if (*c < '0' || *c > '9') is_symbol = true;
}
if (!is_symbol) {
free(addr_str);
continue; // address is decimal constant
}
// search for symbol in list
bool found = false;
for (int s = 0; s < predef_symbol_cnt + user_symbol_cnt; s++) {
if (strcmp(addr_str, symbols[s].label) == 0) {
// overwrite asm line with decimal constant
sprintf(asm_lines[i], "@%d", symbols[s].addr);
found = true;
free(addr_str);
break;
}
}
if (!found) {
// add symbol to list
symbols[predef_symbol_cnt + user_symbol_cnt] = (struct symbol) {addr_str, addr};
sprintf(asm_lines[i], "@%d", addr);
user_symbol_cnt++;
addr++;
}
}
// start assembling
uint16_t *binary = calloc(32768, 2);
size_t inst_cnt = 0; // current no. of instructions in binary
for (char **line = asm_lines; *line != NULL; line++) {
*(binary + inst_cnt) = assemble_inst(*line);
inst_cnt++;
}
for (char **line = asm_lines; *line != NULL; line++) free(*line);
free(asm_lines);
for (int s = predef_symbol_cnt; s < predef_symbol_cnt + user_symbol_cnt; s++) {
free(symbols[s].label);
}
// write binary
// output_fn = input_fn[:-4] + ".hack" if input_fn.endswith(".asm") else input_fn + ".hack"
int input_fn_len = strlen(input_fn);
char *output_fn = malloc(input_fn_len + 6);
strcpy(output_fn, input_fn);
if (input_fn_len >= 4 && strcmp(input_fn + input_fn_len - 4, ".asm") == 0) {
sprintf(output_fn + input_fn_len - 4, ".hack");
} else {
sprintf(output_fn + input_fn_len, ".hack");
}
FILE *output_file = fopen(output_fn, "w");
write_binary(output_file, binary, inst_cnt);
fclose(output_file);
free(binary);
printf("Binary written to %s\n", output_fn);
free(output_fn);
return inst_cnt;
}
int main(int argc, char *argv[]) {
assembler(argv[1]);
return 0;
}
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