Skip underscores

[headius]

Several systems now allow for understands in numeric literals, so skip them if encountered.

This may be too permissive and will allow any number of underscores anywhere in the numeric part of the incoming string.

(I am attempting to adapt this library for use in JRuby's float parser, which must allow underscores.)

[wrandelshofer]

This class is specifically designed as a drop-in for the Java API Double.valueOf(String).
This is why, it only accepts the same syntax that is specified here: javadoc of Double.valueOf(String).

Ideally, you can use class ConfigurableDoubleParser instead.
Like so:

import ch.randelshofer.fastdoubleparser.ConfigurableDoubleParser;
import ch.randelshofer.fastdoubleparser.NumberFormatSymbols;

import java.util.Set;

public class MyMain {
    public static void main(String... args) {
        var parser = new ConfigurableDoubleParser(NumberFormatSymbols.fromDefault()
                .withGroupingSeparator(Set.<Character>of('_')));
        var result = parser.parseDouble("1_234.5e6");
        System.out.println(result);
    }
}

[headius]

I can see that this does fix the issues for me, thank you! I withdraw my PR and we can continue discussion in jruby/jruby#9150.