# Advanced User Guide

## Additional Features

The main [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} should be enough to give you a tour through all the main features of **FastAPI**.

In the next sections you will see other options, configurations, and additional features.

/// tip

The next sections are **not necessarily "advanced"**.

And it's possible that for your use case, the solution is in one of them.

///

 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class Hashing {
  private Hashing() {}

  /*
   * These should be ints, but we need to use longs to force GWT to do the multiplications with
   * enough precision.
   */
  private static final long C1 = 0xcc9e2d51;
  private static final long C2 = 0x1b873593;

  /*
   * This method was rewritten in Java from an intermediate step of the Murmur hash function in

      added += q.drainTo(buffer, numElements - added);
      if (added < numElements) { // not enough elements immediately available; will have to poll
        E e = q.poll(deadline - System.nanoTime(), NANOSECONDS);
        if (e == null) {
          break; // we already waited enough, and there are no more elements in sight
        }
        buffer.add(e);
        added++;
      }
    }

   * during which the {@code RateLimiter} smoothly ramps up its rate, until it reaches its maximum
   * rate at the end of the period (as long as there are enough requests to saturate it). Similarly,
   * if the {@code RateLimiter} is left <i>unused</i> for a duration of {@code warmupPeriod}, it
   * will gradually return to its "cold" state, i.e. it will go through the same warming up process

   * during which the {@code RateLimiter} smoothly ramps up its rate, until it reaches its maximum
   * rate at the end of the period (as long as there are enough requests to saturate it). Similarly,
   * if the {@code RateLimiter} is left <i>unused</i> for a duration of {@code warmupPeriod}, it
   * will gradually return to its "cold" state, i.e. it will go through the same warming up process

      added += q.drainTo(buffer, numElements - added);
      if (added < numElements) { // not enough elements immediately available; will have to poll
        E e = q.poll(deadline - System.nanoTime(), NANOSECONDS);
        if (e == null) {
          break; // we already waited enough, and there are no more elements in sight
        }
        buffer.add(e);
        added++;
      }
    }

		if metadata.VersionID == "" {
			vid = nullVersionID
		}
		vidMap[vid]++
		etags[index] = metadata.Metadata["etag"]
	}

	for _, count := range vidMap {
		// do we have enough common versions
		// that have enough quorum to satisfy
		// the etag.
		if count >= quorum {
			return etags
		}
	}

	return make([]string, len(partsMetadata))
}

 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class Hashing {
  private Hashing() {}

  /*
   * These should be ints, but we need to use longs to force GWT to do the multiplications with
   * enough precision.
   */
  private static final long C1 = 0xcc9e2d51;
  private static final long C2 = 0x1b873593;

  /*
   * This method was rewritten in Java from an intermediate step of the Murmur hash function in

	r2b := make([]int, len(readers))
	for i := range r2b {
		r2b[i] = i
	}
	bufs := make([][]byte, len(readers))
	shardSize := int(e.ShardSize())
	var b []byte

	// We should always have enough capacity, but older objects may be bigger
	// we do not need stashbuffer for them.
	if globalBytePoolCap.Load().WidthCap() >= len(readers)*shardSize {
		// Fill buffers
		b = globalBytePoolCap.Load().Get()

   * {@code long} value in little-endian order.
   *
   * @throws IllegalStateException if {@code bits() < 64}
   */
  public abstract long asLong();

  /**
   * If this hashcode has enough bits, returns {@code asLong()}, otherwise returns a {@code long}
   * value with {@code asBytes()} as the least-significant bytes and {@code 0x00} as the remaining
   * most-significant bytes.
   *