About the CharMatcher.WHITESPACE implementation

Question

When i looked up the implementation of CharMatcher and notice a field WHITESPACE_MULTIPLIER=1682554634 , then i set this value to 1582554634

Answer 1

I'm not sure if the generator still exists somewhere, but it can be recreated easily. The class Result contains the data used in the implementation of CharMatcher.WHITESPACE:

static class Result {
    private int shift;
    private int multiplier;
    private String table;
}

// No duplicates allowed.
private final String allMatchingString = "\u2002\r\u0085\u200A\u2005\u2000"
        + "\u2029\u000B\u2008\u2003\u205F\u1680"
        + "\u0009\u0020\u2006\u2001\u202F\u00A0\u000C\u2009"
        + "\u2004\u2028\n\u2007\u3000";

public Result generate(String allMatchingString) {
    final char[] allMatching = allMatchingString.toCharArray();
    final char filler = allMatching[allMatching.length - 1];
    final int shift = Integer.numberOfLeadingZeros(allMatching.length);
    final char[] table = new char[1 << (32 - shift)];
    OUTER: for (int i=0; i>=0; ++i) {
        final int multiplier = 123456789 * i; // Jumping a bit makes the search faster.
        Arrays.fill(table, filler);
        for (final char c : allMatching) {
            final int index = (multiplier * c) >>> shift;
            if (table[index] != filler) continue OUTER; // Conflict found.
            table[index] = c;
        }
        return new Result(shift, multiplier, new String(table));
    }
    return null; // No solution exists.
}

It generates a different multiplier, but this doesn't matter.

In case no solution for a given allMatchingString exists, you can decrement shift and try again.