private static char[] fourDigitHexString(final char c) {
        final char[] hex = new char[4];
        int in = ((c) & 0xFFFF);
        for (int i = 3; i >= 0; --i) {
            hex[i] = DIGITS[in & 0xF];
            in >>>= 4;
        }
        return hex;
    }
Convert simple metrics snapshots into jdisc state snapshots.

@author arnej27959
container-core/src/main/java/com/yahoo/metrics/simple/jdisc/SnapshotConverter.java