// Relies on the correctness of log2(BigInteger, {HALF_UP,HALF_DOWN}).
public void testLog2HalfEven() {
for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
int halfEven = BigIntegerMath.log2(x, HALF_EVEN);
// Now figure out what rounding mode we should behave like (it depends if FLOOR was
// odd/even).
boolean floorWasEven = (BigIntegerMath.log2(x, FLOOR) & 1) == 0;
assertEquals(BigIntegerMath.log2(x, floorWasEven ? HALF_DOWN : HALF_UP), halfEven);
}
}
public void testLog2Ceiling() {
for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
for (RoundingMode mode : asList(CEILING, UP)) {
int result = BigIntegerMath.log2(x, mode);
assertTrue(ZERO.setBit(result).compareTo(x) >= 0);
assertTrue(result == 0 || ZERO.setBit(result - 1).compareTo(x) < 0);
}
}
}
public void testLog2Floor() {
for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
for (RoundingMode mode : asList(FLOOR, DOWN)) {
int result = BigIntegerMath.log2(x, mode);
assertTrue(ZERO.setBit(result).compareTo(x) <= 0);
assertTrue(ZERO.setBit(result + 1).compareTo(x) > 0);
}
}
}
public void testLog2NegativeAlwaysThrows() {
for (RoundingMode mode : ALL_ROUNDING_MODES) {
try {
BigIntegerMath.log2(BigInteger.valueOf(-1), mode);
fail("Expected IllegalArgumentException");
} catch (IllegalArgumentException expected) {
}
}
}
public void testLog2HalfDown() {
for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
int result = BigIntegerMath.log2(x, HALF_DOWN);
BigInteger x2 = x.pow(2);
// x^2 <= 2^(2 * result + 1), or else we would have rounded up
assertTrue(ZERO.setBit(2 * result + 1).compareTo(x2) >= 0);
// x^2 > 2^(2 * result - 1), or else we would have rounded down
assertTrue(result == 0 || ZERO.setBit(2 * result - 1).compareTo(x2) < 0);
}
}
// Relies on the correctness of isPowerOfTwo(BigInteger).
public void testLog2Exact() {
for (BigInteger x : POSITIVE_BIGINTEGER_CANDIDATES) {
// We only expect an exception if x was not a power of 2.
boolean isPowerOf2 = BigIntegerMath.isPowerOfTwo(x);
try {
assertEquals(x, ZERO.setBit(BigIntegerMath.log2(x, UNNECESSARY)));
assertTrue(isPowerOf2);
} catch (ArithmeticException e) {
assertFalse(isPowerOf2);
}
}
}
