singlepass.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

// itoa() manual implementation as its not ANSI Standard
//start of itoa block
// Function to swap two numbers
void swap(char *x, char *y) {
    char t = *x; *x = *y; *y = t;
}
 
// Function to reverse `buffer[i…j]`
char* reverse(char *buffer, int i, int j)
{
    while (i < j) {
        swap(&buffer[i++], &buffer[j--]);
    }
 
    return buffer;
}
 
// Iterative function to implement `itoa()` function in C
char* itoa(int value, char* buffer, int base)
{
    // invalid input
    if (base < 2 || base > 32) {
        return buffer;
    }
 
    // consider the absolute value of the number
    int n = abs(value);
 
    int i = 0;
    while (n)
    {
        int r = n % base;
 
        if (r >= 10) {
            buffer[i++] = 65 + (r - 10);
        }
        else {
            buffer[i++] = 48 + r;
        }
 
        n = n / base;
    }
 
    // if the number is 0
    if (i == 0) {
        buffer[i++] = '0';
    }
 
    // If the base is 10 and the value is negative, the resulting string
    // is preceded with a minus sign (-)
    // With any other base, value is always considered unsigned
    if (value < 0 && base == 10) {
        buffer[i++] = '-';
    }
 
    buffer[i] = '\0'; // null terminate string
 
    // reverse the string and return it
    return reverse(buffer, 0, i - 1);
}
//end of itoa block


void main()
{
    char opcode[10], operand[10], label[10], a[10], ad[10], symbol[10], ch;
    char code[10][10], code1[10][10] = {"33", "44", "53", "57"};
    char mnemonic[10][10] = {"START", "LDA", "STA", "LDCH", "STCH", "END"};
    char mnemonic1[10][10] = {"LDA", "STA", "LDCH", "STCH"};
    int locctr, start, length, i = 0, j = 0, k, l = 0;
    int st, diff, address, add, len, actual_len, finaddr, prevaddr;
    FILE *fp1, *fp2, *fp3, *fp4, *fp5, *fp6, *fp7;

    fp1 = fopen("input.txt", "r");
    fp2 = fopen("symtab.txt", "w");
    fp3 = fopen("intermediate.txt", "w");
    fscanf(fp1, "%s%s%s", label, opcode, operand);
    if (strcmp(opcode, "START") == 0)
    {
        start = atoi(operand);
        locctr = start;
        fprintf(fp3, "%s\t%s\t%s\n", label, opcode, operand);
        fscanf(fp1, "%s%s%s", label, opcode, operand);
    }
    else
        locctr = 0;
    while (strcmp(opcode, "END") != 0)
    {
        fprintf(fp3, "%d", locctr);
        if (strcmp(label, "**") != 0)
            fprintf(fp2, "%s\t%d\n", label, locctr);
        strcpy(code[i], mnemonic[j]);
        while (strcmp(mnemonic[j], "END") != 0)
        {
            if (strcmp(opcode, mnemonic[j]) == 0)
            {
                locctr += 3;
                break;
            }
            strcpy(code[i], mnemonic[j]);
            j++;
        }
        if (strcmp(opcode, "WORD") == 0)
            locctr += 3;
        else if (strcmp(opcode, "RESW") == 0)
            locctr += (3 * (atoi(operand)));
        else if (strcmp(opcode, "RESB") == 0)
            locctr += (atoi(operand));
        else if (strcmp(opcode, "BYTE") == 0)
            ++locctr;
        fprintf(fp3, "\t%s\t%s\t%s\n", label, opcode, operand);
        fscanf(fp1, "%s%s%s", label, opcode, operand);
    }
    fprintf(fp3, "%d\t%s\t%s\t%s\n", locctr, label, opcode, operand);
    length = locctr - start;

    fclose(fp3);
    fclose(fp2);
    fclose(fp1);

    printf("\n\nThe contents of Input file:\n\n");
    fp1 = fopen("input.txt", "r");
    ch = fgetc(fp1);
    while (ch != EOF)
    {
        printf("%c", ch);
        ch = fgetc(fp1);
    }
    printf("\n\nLength of the input program is %d.", length);
    printf("\n\nThe contents of Symbol Table:\n\n");
    fp2 = fopen("symtab.txt", "r");
    ch = fgetc(fp2);
    while (ch != EOF)
    {
        printf("%c", ch);
        ch = fgetc(fp2);
    }

    fclose(fp2);
    fclose(fp1);

    fp4 = fopen("output.txt", "w");
    fp5 = fopen("symtab.txt", "r");
    fp6 = fopen("intermediate.txt", "r");
    fp7 = fopen("objcode.txt", "w");
    fscanf(fp6, "%s%s%s", label, opcode, operand);
    while (strcmp(opcode, "END") != 0)
    {
        prevaddr = address;
        fscanf(fp6, "%d%s%s%s", &address, label, opcode, operand);
    }
    finaddr = address;
    fclose(fp6);
    fp6 = fopen("intermediate.txt", "r");
    fscanf(fp6, "%s%s%s", label, opcode, operand);
    if (strcmp(opcode, "START") == 0)
    {
        fprintf(fp4, "\t%s\t%s\t%s\n", label, opcode, operand);
        fprintf(fp7, "H^%s^00%s^00%d\n", label, operand, finaddr);
        fscanf(fp6, "%d%s%s%s", &address, label, opcode, operand);
        st = address;
        diff = prevaddr - st;
        fprintf(fp7, "T^00%d^%d", address, diff);
    }
    while (strcmp(opcode, "END") != 0)
    {
        if (strcmp(opcode, "BYTE") == 0)
        {
            fprintf(fp4, "%d\t%s\t%s\t%s\t", address, label, opcode, operand);
            len = strlen(operand);
            actual_len = len - 3;
            fprintf(fp7, "^");
            for (k = 2; k < (actual_len + 2); k++)
            {
                itoa(operand[k], ad, 16);
                fprintf(fp4, "%s", ad);
                fprintf(fp7, "%s", ad);
            }
            fprintf(fp4, "\n");
        }
        else if (strcmp(opcode, "WORD") == 0)
        {
            len = strlen(operand);
            itoa(atoi(operand), a, 10);
            fprintf(fp4, "%d\t%s\t%s\t%s\t00000%s\n", address, label, opcode, operand, a);
            fprintf(fp7, "^00000%s", a);
        }
        else if ((strcmp(opcode, "RESB") == 0) || (strcmp(opcode, "RESW") == 0))
            fprintf(fp4, "%d\t%s\t%s\t%s\n", address, label, opcode, operand);
        else
        {
            while (strcmp(opcode, mnemonic1[l]) != 0)
                l++;
            if (strcmp(operand, "COPY") == 0)
                fprintf(fp4, "%d\t%s\t%s\t%s\t%s0000\n", address, label, opcode, operand, code1[l]);
            else
            {
                rewind(fp5);
                fscanf(fp5, "%s%d", symbol, &add);
                while (strcmp(operand, symbol) != 0)
                    fscanf(fp5, "%s%d", symbol, &add);
                fprintf(fp4, "%d\t%s\t%s\t%s\t%s%d\n", address, label, opcode, operand, code1[l], add);
                fprintf(fp7, "^%s%d", code1[l], add);
            }
        }
        fscanf(fp6, "%d%s%s%s", &address, label, opcode, operand);
    }
    fprintf(fp4, "%d\t%s\t%s\t%s\n", address, label, opcode, operand);
    fprintf(fp7, "\nE^00%d", st);
    printf("\nObject Program has been generated.");

    fclose(fp7);
    fclose(fp6);
    fclose(fp5);
    fclose(fp4);

    printf("\n\nObject Program:\n\n");
    fp7 = fopen("objcode.txt", "r");
    ch = fgetc(fp7);
    while (ch != EOF)
    {
        printf("%c", ch);
        ch = fgetc(fp7);
    }
    fclose(fp7);
}