Class LongRange

src/jvm/clojure/lang/LongRange.java:22–259

Implements the special common case of a finite range based on long start, end, and step, with no more than Integer.MAX_VALUE items.

 * with no more than Integer.MAX_VALUE items.
 */
public class LongRange extends ASeq implements Counted, IChunkedSeq, IReduce, IDrop {

private static final long serialVersionUID = -1467242400566893909L;

// Invariants guarantee this is never an empty or infinite seq
//   assert(start != end && step != 0)
final long start;
final long end;
final long step;
final int count;

private LongRange(long start, long end, long step, int count){
    this.start = start;
    this.end = end;
    this.step = step;
    this.count = count;
}

private LongRange(IPersistentMap meta, long start, long end, long step, int count){
    super(meta);
    this.start = start;
    this.end = end;
    this.step = step;
    this.count = count;
}

// returns exact size of remaining items OR throws ArithmeticException for overflow case
static long rangeCount(long start, long end, long step) {
    // (1) count = ceiling ( (end - start) / step )
    // (2) ceiling(a/b) = (a+b+o)/b where o=-1 for positive stepping and +1 for negative stepping
    // thus: count = end - start + step + o / step
    return Numbers.add(Numbers.add(Numbers.minus(end, start), step), step > 0 ? -1 : 1) / step;
}

public static ISeq create(long end) {
    if(end > 0) {
        try {
            return new LongRange(0L, end, 1L, Math.toIntExact(rangeCount(0L, end, 1L)));
        } catch(ArithmeticException e) {
            return Range.create(end);  // count > Integer.MAX_VALUE
        }
    } else {
        return PersistentList.EMPTY;
    }
}

public static ISeq create(long start, long end) {
    if(start >= end) {
        return PersistentList.EMPTY;
    } else {
        try {
            return new LongRange(start, end, 1L, Math.toIntExact(rangeCount(start, end, 1L)));
        } catch(ArithmeticException e) {
            return Range.create(start, end);
        }
    }
}