private static char highSurrogate(int codePoint) {
            return (char) ((MIN_HIGH_SURROGATE - (MIN_SUPPLEMENTARY_CODE_POINT >>> 10)) + (codePoint >>> 10));
        }
Returns the actual value of the trailing byte (removes the prefix '10') for composition.
jraft-core/src/main/java/com/alipay/sofa/jraft/util/internal/UnsafeUtf8Util.java