/**
* Determines if the supplied double fits into this float as a subnormal.
*
* @param Float64 $float The float (represented in 64 bit).
* @return boolean Whether the double fits as a subnormal inside this float type.
*/
public static function fitsAsSubnormal(Float64 $float)
{
// If the exponent is lower than the lowest subnormal, it can't fit
if ($float->getExponent() < 1 - static::getExponentOffset() - static::getNumSignificandBits()) {
return false;
}
// If the exponent is larger than the negative exponent offset, it can't fit
if ($float->getExponent() > 1 - static::getExponentOffset()) {
return false;
}
// Make sure the significand (+1 implicit digit) actually fits in the required number of bits
if (($float->getSignificand() << 1) + 1 > self::getMaxSignificand()) {
return false;
}
// Trash all the trailing zeros in the significand
$significand = $float->getSignificand();
// Convert the significand into a binary string
$significand = decbin($significand);
// Trim leading zeros
$significand = ltrim($significand, '0');
// Add a 1 to the start of the string, it's implicit in normal numbers, but not in subnormals
$significand = bindec('1' . $significand);
// Determine the number of "exponent bits" you have free
$exponentBits = static::getNumSignificandBits() - strlen($significand);
// Compute the minimum exponent you can do with those free bits
$minExponent = -1 * (static::getExponentOffset() + $exponentBits);
// If the exponent fits
return $float->getExponent() >= $minExponent;
}
/**
* Decodes a double value.
*
* @param int $length Size of the number, in bytes.
* @param array $bytes The messages byte array.
* @return float The decoded double.
* @throws CborException If there aren't enough bytes in the remaining byte string.
*/
private static function decodeDouble($length, &$bytes)
{
// Not enough bytes
if ($length > count($bytes)) {
throw new CborException("The supplied byte string is too short to decode the specified double type.");
}
// Grab the required number of bytes
$byteArray = array_splice($bytes, 0, $length);
// Unpack a 32 bit double
if ($length == 4) {
return Float32::decode($byteArray);
} else {
if ($length == 8) {
return Float64::decode($byteArray);
} else {
return Float16::decode($byteArray);
}
}
}
