Value GranularityRounderPowersOfTwo::roundDown(Value value) {
uassertNonNegativeNumber(value);
if (value.coerceToDouble() == 0.0) {
return value;
}
Value exp;
if (value.getType() == BSONType::NumberDouble) {
exp = Value(static_cast<int>(std::ceil(std::log2(value.getDouble())) - 1.0));
} else if (value.getType() == BSONType::NumberDecimal) {
Decimal128 input = value.getDecimal();
exp = Value(Decimal128(
static_cast<int>((std::ceil(input.logarithm(Decimal128(2)).toDouble()) - 1.0))));
} else {
long long number = value.getLong();
int leadingZeros = countLeadingZeros64(number);
int trailingZeros = countTrailingZeros64(number);
if (leadingZeros + trailingZeros == 63) {
// If number is a power of 2, then we need to subtract an extra 1 so we round down to
// the next power of 2.
exp = Value(63 - leadingZeros - 1);
} else {
exp = Value(63 - leadingZeros);
}
}
return ExpressionPow::create(getExpCtx(), Value(2), exp)->evaluate(Document());
}
Value GranularityRounderPowersOfTwo::roundUp(Value value) {
uassertNonNegativeNumber(value);
if (value.coerceToDouble() == 0.0) {
return value;
}
Value exp;
if (value.getType() == BSONType::NumberDouble) {
exp = Value(static_cast<int>(std::floor(std::log2(value.getDouble())) + 1.0));
} else if (value.getType() == BSONType::NumberDecimal) {
Decimal128 input = value.getDecimal();
exp = Value(Decimal128(
static_cast<int>((std::floor(input.logarithm(Decimal128(2)).toDouble()) + 1.0))));
} else {
long long number = value.getLong();
// We can find the log_2 of 'number' by counting the number of leading zeros to find its
// first bit set. This is safe to do because we are working with positive values.
exp = Value(63 - countLeadingZeros64(number) + 1);
}
return ExpressionPow::create(getExpCtx(), Value(2), exp)->evaluate(Document());
}