Add hack-as-min.c

1 files changed, 268 insertions, 0 deletions

diff --git a/projects/06/hack-as/hack-as.min.c b/projects/06/hack-as/hack-as.min.c
new file mode 100644
index 0000000..5d7252f
--- /dev/null
+++ b/projects/06/hack-as/hack-as.min.c
@@ -0,0 +1,268 @@
+#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;
+}