gecko-dev/js/js2/java/BinaryDigitReader.java

/* -*- Mode: java; tab-width: 8 -*-
 * Copyright © 1997, 1998 Netscape Communications Corporation,
 * All Rights Reserved.
 */

final class BinaryDigitReader {
    int lgBase;			// Logarithm of base of number
    int digit;			// Current digit value in radix given by base
    int digitPos;		// Bit position of last bit extracted from digit
    String digits;		// String containing the digits
    int start;			// Index of the first remaining digit
    int end;			// Index past the last remaining digit

    BinaryDigitReader(int base, String digits, int start, int end) {
        lgBase = 0;
        while (base != 1) {
            lgBase++;
            base >>= 1;
        }
        digitPos = 0;
        this.digits = digits;
        this.start = start;
        this.end = end;
    }

    /* Return the next binary digit from the number or -1 if done */
    int getNextBinaryDigit()
    {
        if (digitPos == 0) {
            if (start == end)
                return -1;

            char c = digits.charAt(start++);
            if ('0' <= c && c <= '9')
                digit = c - '0';
            else if ('a' <= c && c <= 'z')
                digit = c - 'a' + 10;
            else digit = c - 'A' + 10;
            digitPos = lgBase;
        }
        return digit >> --digitPos & 1;
    }
}