long delta = a - b; // can't overflow, since a and b are nonnegative

      long minDeltaOrZero = delta & (delta >> (Long.SIZE - 1));
      // equivalent to Math.min(delta, 0)

      a = delta - minDeltaOrZero - minDeltaOrZero; // sets a to Math.abs(a - b)
      // a is now nonnegative and even

      b += minDeltaOrZero; // sets b to min(old a, b)

      long delta = a - b; // can't overflow, since a and b are nonnegative

      long minDeltaOrZero = delta & (delta >> (Long.SIZE - 1));
      // equivalent to Math.min(delta, 0)

      a = delta - minDeltaOrZero - minDeltaOrZero; // sets a to Math.abs(a - b)
      // a is now nonnegative and even

      b += minDeltaOrZero; // sets b to min(old a, b)

   * interpreted as an unsigned 32-bit value. Specifically, the sign bit of {@code bits} is
   * interpreted as a normal bit, and all other bits are treated as usual.
   *
   * <p>If the argument is nonnegative, the returned result will be equal to {@code bits},
   * otherwise, the result will be equal to {@code 2^32 + bits}.
   *
   * <p>To represent unsigned decimal constants, consider {@link #valueOf(long)} instead.
   *

   * interpreted as an unsigned 32-bit value. Specifically, the sign bit of {@code bits} is
   * interpreted as a normal bit, and all other bits are treated as usual.
   *
   * <p>If the argument is nonnegative, the returned result will be equal to {@code bits},
   * otherwise, the result will be equal to {@code 2^32 + bits}.
   *
   * <p>To represent unsigned decimal constants, consider {@link #valueOf(long)} instead.
   *

   * interpreted as an unsigned 64-bit value. Specifically, the sign bit of {@code bits} is
   * interpreted as a normal bit, and all other bits are treated as usual.
   *
   * <p>If the argument is nonnegative, the returned result will be equal to {@code bits},
   * otherwise, the result will be equal to {@code 2^64 + bits}.
   *
   * <p>To represent decimal constants less than {@code 2^63}, consider {@link #valueOf(long)}

   * interpreted as an unsigned 64-bit value. Specifically, the sign bit of {@code bits} is
   * interpreted as a normal bit, and all other bits are treated as usual.
   *
   * <p>If the argument is nonnegative, the returned result will be equal to {@code bits},
   * otherwise, the result will be equal to {@code 2^64 + bits}.
   *
   * <p>To represent decimal constants less than {@code 2^63}, consider {@link #valueOf(long)}

	// That means we'd need 65 bits to encode all possible indexes, from -2^63 to 2^64-1.
	// Instead, we keep track of whether x should be interpreted as signed or unsigned.
	// y is known to be nonnegative and to fit in an int.
	signed bool
	code   boundsErrorCode
}

type boundsErrorCode uint8

const (
	boundsIndex boundsErrorCode = iota // s[x], 0 <= x < len(s) failed

   *
   * <p><b>Java 11+ users:</b> use {@code string.repeat(count)} instead.
   *
   * @param string any non-null string
   * @param count the number of times to repeat it; a nonnegative integer
   * @return a string containing {@code string} repeated {@code count} times (the empty string if
   *     {@code count} is zero)
   * @throws IllegalArgumentException if {@code count} is negative
   */

	// r = CT_SELECT(r_prime IF flipped_sign_sqrt | flipped_sign_sqrt_i ELSE r)
	rr.Select(rPrime, rr, flippedSignSqrt|flippedSignSqrtI)

	r.Absolute(rr) // Choose the nonnegative square root.
	return r, correctSignSqrt | flippedSignSqrt

   * example, {@code repeat("hey", 3)} returns the string {@code "heyheyhey"}.
   *
   * @param string any non-null string
   * @param count the number of times to repeat it; a nonnegative integer
   * @return a string containing {@code string} repeated {@code count} times (the empty string if
   *     {@code count} is zero)
   * @throws IllegalArgumentException if {@code count} is negative
   */