/* Assembler for LC */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define MAXLINELENGTH 1000
#define MAXNUMLABELS 65536
#define MAXLABELLENGTH 7 /* includes the null character termination */

#define ADD 0
#define NAND 1
#define LW 2
#define SW 3
#define BEQ 4
#define MULT 5
#define HALT 6
#define NOOP 7

int readAndParse(FILE *, char *, char *, char *, char *, char *);
int translateSymbol(char [MAXNUMLABELS][MAXLABELLENGTH], int labelAddress[], int, char *);
int isNumber(char *);
void testRegArg(char *);
void testAddrArg(char *);

int
main(int argc, char *argv[])
{
    char *inFileString, *outFileString;
    FILE *inFilePtr, *outFilePtr;
    int address;
    char label[MAXLINELENGTH], opcode[MAXLINELENGTH], arg0[MAXLINELENGTH],
	arg1[MAXLINELENGTH], arg2[MAXLINELENGTH], argTmp[MAXLINELENGTH];
    int i;
    int numLabels=0;
    int num;
    int addressField;

    char labelArray[MAXNUMLABELS][MAXLABELLENGTH];
    int labelAddress[MAXNUMLABELS];

    if (argc != 3) {
	printf("error: usage: %s <assembly-code-file> <machine-code-file>\n",
	    argv[0]);
	exit(1);
    }

    inFileString = argv[1];
    outFileString = argv[2];

    inFilePtr = fopen(inFileString, "r");
    if (inFilePtr == NULL) {
	printf("error in opening %s\n", inFileString);
	exit(1);
    }
    outFilePtr = fopen(outFileString, "w");
    if (outFilePtr == NULL) {
	printf("error in opening %s\n", outFileString);
	exit(1);
    }

    /* map symbols to addresses */

    /* assume address start at 0 */
    for (address=0; readAndParse(inFilePtr, label, opcode, arg0, arg1, arg2);
	    address++) {
	/*
	printf("%d: label=%s, opcode=%s, arg0=%s, arg1=%s, arg2=%s\n",
	    address, label, opcode, arg0, arg1, arg2);
	*/

	/* check for illegal opcode */
	if (strcmp(opcode, "add") && strcmp(opcode, "nand") &&
	        strcmp(opcode, "lw") && strcmp(opcode, "sw") &&
		strcmp(opcode, "beq") && strcmp(opcode, "mult") &&
		strcmp(opcode, "halt") && strcmp(opcode, "noop") &&
		strcmp(opcode, ".fill") ) {
	    printf("error: unrecognized opcode %s at address %d\n", opcode,
		    address);
	    exit(1);
	}

	/* check register fields */
	if (!strcmp(opcode, "add") || !strcmp(opcode, "nand") ||
		!strcmp(opcode, "lw") || !strcmp(opcode, "sw") ||
		!strcmp(opcode, "beq") || !strcmp(opcode, "mult")) {
	    testRegArg(arg0);
	    testRegArg(arg1);
	}
	if (!strcmp(opcode, "add") || !strcmp(opcode, "nand") ||
		!strcmp(opcode, "mult")) {
	    testRegArg(arg2);
	}

	/* check addressField */
	if (!strcmp(opcode, "lw") || !strcmp(opcode, "sw") ||
		!strcmp(opcode, "beq")) {
	    testAddrArg(arg2);
	}
	if (!strcmp(opcode, ".fill")) {
	    testAddrArg(arg0);
	}

	/* check for enough arguments */
	if ( (strcmp(opcode, "halt") && strcmp(opcode, "noop") &&
	      strcmp(opcode, ".fill") && arg2[0]=='\0') ||
	     (!strcmp(opcode, ".fill") && arg0[0]=='\0')) {
	    printf("error at address %d: not enough arguments\n", address);
	    exit(2);
	}

	if (label[0] != '\0') {
	    /* check for labels that are too long */
	    if (strlen(label) >= MAXLABELLENGTH) {
		printf("label too long\n");
		exit(2);
	    }

	    /* make sure label starts with letter */
	    if (! sscanf(label, "%[a-zA-Z]", argTmp) ) {
	        printf("label doesn't start with letter\n");
		exit(2);
	    }

	    /* make sure label consists of only letters and numbers */
	    sscanf(label, "%[a-zA-Z0-9]", argTmp);
	    if (strcmp(argTmp, label)) {
	        printf("label has character other than letters and numbers\n");
		exit(2);
	    }

	    /* look for duplicate label */
	    for (i=0; i<numLabels; i++) {
		if (!strcmp(label, labelArray[i])) {
		    printf("error: duplicate label %s at address %d\n",
			label, address);
		    exit(1);
		}
	    }
	    /* see if there are too many labels */
	    if (numLabels >= MAXNUMLABELS) {
		printf("error: too many labels (label=%s)\n", label);
		exit(2);
	    }

	    strcpy(labelArray[numLabels], label);
	    labelAddress[numLabels++] = address;
	}
    }

    for (i=0; i<numLabels; i++) {
	/* printf("%s = %d\n", labelArray[i], labelAddress[i]); */
    }

    /* now do second pass (print machine code, with symbols filled in as
	addresses) */
    rewind(inFilePtr);
    for (address=0; readAndParse(inFilePtr, label, opcode, arg0, arg1, arg2);
	    address++) {
	if (!strcmp(opcode, "add")) {
	    num = (ADD << 22) | (atoi(arg0) << 19) | (atoi(arg1) << 16)
		    | atoi(arg2);
	} else if (!strcmp(opcode, "nand")) {
	    num = (NAND << 22) | (atoi(arg0) << 19) | (atoi(arg1) << 16)
		    | atoi(arg2);
	} else if (!strcmp(opcode, "mult")) {
	    num = (MULT << 22) | (atoi(arg0) << 19) | (atoi(arg1) << 16)
		    | atoi(arg2);
	} else if (!strcmp(opcode, "halt")) {
	    num = (HALT << 22);
	} else if (!strcmp(opcode, "noop")) {
	    num = (NOOP << 22);
	} else if (!strcmp(opcode, "lw") || !strcmp(opcode, "sw") ||
		   !strcmp(opcode, "beq")) {
	    /* if arg2 is symbolic, then translate into an address */
	    if (!isNumber(arg2)) {
		addressField = translateSymbol(labelArray, labelAddress,
					    numLabels, arg2);
		/*
		printf("%s being translated into %d\n", arg2, addressField);
		*/
		if (!strcmp(opcode, "beq")) {
		    addressField = addressField-address-1;
		}
	    } else {
		addressField = atoi(arg2);
	    }


	    if (addressField < -32768 || addressField > 32767) {
		printf("error: offset %d out of range\n", addressField);
		exit(1);
	    }

	    /* truncate the offset field, in case it's negative */
	    addressField = addressField & 0xFFFF;

	    if (!strcmp(opcode, "beq")) {
		num = (BEQ << 22) | (atoi(arg0) << 19) | (atoi(arg1) << 16)
		    | addressField;
	    } else {
		/* lw or sw */
		if (!strcmp(opcode, "lw")) {
		    num = (LW << 22) | (atoi(arg0) << 19) |
			    (atoi(arg1) << 16) | addressField;
		} else {
		    num = (SW << 22) | (atoi(arg0) << 19) |
			    (atoi(arg1) << 16) | addressField;
		}
	    }
	} else if (!strcmp(opcode, ".fill")) {
	    if (!isNumber(arg0)) {
		num = translateSymbol(labelArray, labelAddress, numLabels,
					arg0);
	    } else {
		num = atoi(arg0);
	    }
	}
	/* printf("(address %d): %d (hex 0x%x)\n", address, num, num); */
	fprintf(outFilePtr, "%d\n", num);
    }

    exit(0);
}

/*
 * Read and parse a line of the assembly-language file.  Fields are returned
 * in label, opcode, arg0, arg1, arg2 (these strings must have memory already
 * allocated to them).
 *
 * Return values:
 *     0 if reached end of file
 *     1 if all went well
 *
 * exit(1) if line is too long.
 */
int
readAndParse(FILE *inFilePtr, char *label, char *opcode, char *arg0,
    char *arg1, char *arg2)
{
    char line[MAXLINELENGTH];
    char *ptr = line;

    /* delete prior values */
    label[0] = opcode[0] = arg0[0] = arg1[0] = arg2[0] = '\0';

    /* read the line from the assembly-language file */
    if (fgets(line, MAXLINELENGTH, inFilePtr) == NULL) {
	/* reached end of file */
        return(0);
    }

    /* check for line too long */
    if (strlen(line) == MAXLINELENGTH-1) {
	printf("error: line too long\n");
	exit(1);
    }

    /* is there a label? */
    ptr = line;
    if (sscanf(ptr, "%[^\t\n ]", label)) {
	/* successfully read label; advance pointer over the label */
        ptr += strlen(label);
    }

    /*
     * Parse the rest of the line.  Would be nice to have real regular
     * expressions, but scanf will suffice.
     */
    sscanf(ptr, "%*[\t\n\r ]%[^\t\n\r ]%*[\t\n\r ]%[^\t\n\r ]%*[\t\n\r ]%[^\t\n\r ]%*[\t\n\r ]%[^\t\n\r ]",
        opcode, arg0, arg1, arg2);
    return(1);
}

int
translateSymbol(char labelArray[MAXNUMLABELS][MAXLABELLENGTH],
    int labelAddress[MAXNUMLABELS], int numLabels, char *symbol)
{
    int i;

    /* search through address label table */
    for (i=0; i<numLabels && strcmp(symbol, labelArray[i]); i++) {
    }

    if (i>=numLabels) {
	printf("error: missing label %s\n", symbol);
	exit(1);
    }

    return(labelAddress[i]);
}

int
isNumber(char *string)
{
    /* return 1 if string is a number */
    int i;
    return( (sscanf(string, "%d", &i)) == 1);
}

/*
 * Test register argument; make sure it's in range and has no bad characters.
 */
void
testRegArg(char *arg)
{
    int num;
    char c;

    if (atoi(arg) < 0 || atoi(arg) > 7) {
	printf("error: register out of range\n");
	exit(2);
    }
    if (sscanf(arg, "%d%c", &num, &c) != 1) {
	printf("bad character in register argument\n");
	exit(2);
    }
}

/*
 * Test addressField argument.
 */
void
testAddrArg(char *arg)
{
    int num;
    char c;

    /* test numeric addressField */
    if (isNumber(arg)) {
	if (sscanf(arg, "%d%c", &num, &c) != 1) {
	    printf("bad character in addressField\n");
	    exit(2);
	}
    }
}