static void putBytesFromInt(int i, final int offset, final int size, final byte[] buf)
    {
        int q, r;
        int charPos = offset + size;
        char sign = 0;

        if (i < 0)
        {
            sign = '-';
            i = -i;
        }

        // Generate two digits per iteration
        while (i >= 65536)
        {
            q = i / 100;
            // really: r = i - (q * 100);
            r = i - ((q << 6) + (q << 5) + (q << 2));
            i = q;
            buf[--charPos] = (byte) DigitOnes[r];
            buf[--charPos] = (byte) DigitTens[r];
        }

        // Fall thru to fast mode for smaller numbers
        // assert(i <= 65536, i);
        for (;;)
        {
            q = (i * 52429) >>> (16 + 3);
            r = i - ((q << 3) + (q << 1)); // r = i-(q*10) ...
            buf[--charPos] = (byte) digits[r];
            i = q;
            if (i == 0)
                break;
        }
        if (sign != 0)
        {
            buf[--charPos] = (byte) sign;
        }
    }
From {@link java.lang.Integer#toString(int)}
protostuff-api/src/main/java/io/protostuff/StringSerializer.java