public static void getChars(byte b, int index, char[] buf) {
        int i = b;
        int q, r;
        int charPos = index;
        char sign = 0;

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

        // 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] = digits[r];
            i = q;
            if (i == 0) break;
        }
        if (sign != 0) {
            buf[--charPos] = sign;
        }
    }
Places characters representing the integer i into the character array buf. The characters are placed into the
buffer backwards starting with the least significant digit at the specified index (exclusive), and working
backwards from there. Will fail if i == Integer.MIN_VALUE
src/main/java/com/alibaba/fastjson/util/IOUtils.java