/**
* Returns the order of magnitude of the uncertainty as the exponent of
* last significant digit in the amount-string. The value returned by this
* is suitable for use with @see DecimalMath::roundToExponent().
*
* @example: if two digits after the decimal point are significant, this
* returns -2.
*
* @example: if the last two digits before the decimal point are insignificant,
* this returns 2.
*
* Note that this calculation assumes a symmetric uncertainty interval,
* and can be misleading.
*
* @since 0.1
*
* @return int
*/
public function getOrderOfUncertainty()
{
// the desired precision is given by the distance between the amount and
// whatever is closer, the upper or lower bound.
//TODO: use DecimalMath to avoid floating point errors!
$amount = $this->getAmount()->getValueFloat();
$upperBound = $this->getUpperBound()->getValueFloat();
$lowerBound = $this->getLowerBound()->getValueFloat();
$precision = min($amount - $lowerBound, $upperBound - $amount);
if ($precision === 0.0) {
// If there is no uncertainty, the order of uncertainty is a bit more than what we have digits for.
return -strlen($this->amount->getFractionalPart());
}
// e.g. +/- 200 -> 2; +/- 0.02 -> -2
// note: we really want floor( log10( $precision ) ), but have to account for
// small errors made in the floating point operations above.
// @todo: use bcmath (via DecimalMath) to avoid this if possible
$orderOfUncertainty = floor(log10($precision + 5.0E-10));
return (int) $orderOfUncertainty;
}
/**
* Compares this DecimalValue to another DecimalValue.
*
* @since 0.1
*
* @param DecimalValue $that
*
* @throws LogicException
* @return int +1 if $this > $that, 0 if $this == $that, -1 if $this < $that
*/
public function compare(DecimalValue $that)
{
if ($this === $that) {
return 0;
}
$a = $this->getValue();
$b = $that->getValue();
if ($a === $b) {
return 0;
}
if ($a[0] === '+' && $b[0] === '-') {
return 1;
}
if ($a[0] === '-' && $b[0] === '+') {
return -1;
}
// compare the integer parts
$aInt = ltrim($this->getIntegerPart(), '0');
$bInt = ltrim($that->getIntegerPart(), '0');
$sense = $a[0] === '+' ? 1 : -1;
// per precondition, there are no leading zeros, so the longer nummber is greater
if (strlen($aInt) > strlen($bInt)) {
return $sense;
}
if (strlen($aInt) < strlen($bInt)) {
return -$sense;
}
// if both have equal length, compare alphanumerically
$cmp = strcmp($aInt, $bInt);
if ($cmp > 0) {
return $sense;
}
if ($cmp < 0) {
return -$sense;
}
// compare fractional parts
$aFract = rtrim($this->getFractionalPart(), '0');
$bFract = rtrim($that->getFractionalPart(), '0');
// the fractional part is left-aligned, so just check alphanumeric ordering
$cmp = strcmp($aFract, $bFract);
return $cmp > 0 ? $sense : ($cmp < 0 ? -$sense : 0);
}
/**
* Shift the decimal point according to the given exponent.
*
* @param DecimalValue $decimal
* @param int $exponent The exponent to apply (digits to shift by). A Positive exponent
* shifts the decimal point to the right, a negative exponent shifts to the left.
*
* @throws InvalidArgumentException
* @return DecimalValue
*/
public function shift(DecimalValue $decimal, $exponent)
{
if (!is_int($exponent)) {
throw new InvalidArgumentException('$exponent must be an integer');
}
if ($exponent == 0) {
return $decimal;
}
$sign = $decimal->getSign();
$intPart = $decimal->getIntegerPart();
$fractPart = $decimal->getFractionalPart();
if ($exponent < 0) {
$intPart = $this->shiftLeft($intPart, $exponent);
} else {
$fractPart = $this->shiftRight($fractPart, $exponent);
}
$digits = $sign . $intPart . $fractPart;
$digits = $this->stripLeadingZeros($digits);
return new DecimalValue($digits);
}
