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168 lines
7.4 KiB
Markdown
168 lines
7.4 KiB
Markdown
Brick\Math
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==========
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A library to work with arbitrary precision numbers.
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[](http://travis-ci.org/brick/math)
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[](https://coveralls.io/r/brick/math?branch=master)
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[](http://opensource.org/licenses/MIT)
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Installation
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------------
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This library is installable via [Composer](https://getcomposer.org/).
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Just define the following requirement in your `composer.json` file:
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{
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"require": {
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"brick/math": "0.4.*"
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}
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}
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Requirements
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------------
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This library requires PHP 5.6, PHP 7 or [HHVM](http://hhvm.com/).
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Although the library can work seamlessly on any PHP installation, it is highly recommended that you install the
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[GMP](http://php.net/manual/en/book.gmp.php) or [BCMath](http://php.net/manual/en/book.bc.php) extension
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to speed up calculations. The fastest available calculator implementation will be automatically selected at runtime.
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Project status & release process
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--------------------------------
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While this library is still under development, it is well tested and should be stable enough to use in production
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environments.
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The current releases are numbered `0.x.y`. When a non-breaking change is introduced (adding new methods, optimizing
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existing code, etc.), `y` is incremented.
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**When a breaking change is introduced, a new `0.x` version cycle is always started.**
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It is therefore safe to lock your project to a given release cycle, such as `0.4.*`.
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If you need to upgrade to a newer release cycle, check the [release history](https://github.com/brick/math/releases)
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for a list of changes introduced by each further `0.x.0` version.
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Package contents
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----------------
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This library provides the following public classes:
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- `Brick\Math\ArithmeticException`: exception thrown when an error occurs.
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- `Brick\Math\BigInteger`: represents an arbitrary-precision integer number.
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- `Brick\Math\BigDecimal`: represents an arbitrary-precision decimal number.
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- `Brick\Math\BigRational`: represents an arbitrary-precision rational number (fraction).
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- `Brick\Math\RoundingMode`: holds constants for the [rounding modes](#division--rounding-modes).
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Overview
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--------
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### Instantiation
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The constructor of each class is private, you must use a factory method to obtain an instance:
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$integer = BigInteger::of('123456'); // accepts integers and strings
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$decimal = BigDecimal::of('123.456'); // accepts floats, integers and strings
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$rational = BigRational::of('123', '456'); // accepts BigInteger instances, integers and strings
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$rational = BigRational::parse('123/456'); // accepts fraction strings
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Avoid instantiating `BigDecimal` from a `float`: floating-point values are imprecise by design,
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and can lead to unexpected results. Always prefer instantiating from a `string`:
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$decimal = BigDecimal::of(123.456); // avoid!
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$decimal = BigDecimal::of('123.456'); // OK, supports an unlimited number of digits.
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### Immutability
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The `BigInteger`, `BigDecimal` and `BigRational` classes are immutable: their value never changes,
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so that they can be safely passed around. All methods that return a `BigInteger`, `BigDecimal` or `BigRational`
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return a new object, leaving the original object unaffected:
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$ten = BigInteger::of(10);
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echo $ten->plus(5); // 15
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echo $ten->multipliedBy(3); // 30
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### Parameter types
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All methods that accept a number: `plus()`, `minus()`, `multipliedBy()`, etc. accept the same types as `of()` / `parse()`.
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As an example, given the following number:
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$integer = BigInteger::of(123);
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The following lines are equivalent:
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$integer->multipliedBy(123);
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$integer->multipliedBy('123');
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$integer->multipliedBy($integer);
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### Chaining
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All the methods that return a new number can be chained, for example:
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echo BigInteger::of(10)->plus(5)->multipliedBy(3); // 45
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### Division & rounding
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#### BigInteger
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Dividing a `BigInteger` always returns the *quotient* of the division:
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echo BigInteger::of(1000)->dividedBy(3); // 333
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You can get the remainder of the division with the `remainder()` method:
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echo BigInteger::of(1000)->remainder(3); // 1
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You can also get both the quotient and the remainder in a single method call:
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list ($quotient, $remainder) = BigInteger::of(1000)->divideAndRemainder(3);
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#### BigDecimal
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When dividing a `BigDecimal`, if the number cannot be represented at the requested scale, the result needs to be rounded up or down.
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By default, the library assumes that rounding is unnecessary, and throws an exception if rouding was in fact necessary:
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BigDecimal::of('1000.0')->dividedBy(3); // throws an ArithmeticException
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In that case, you need to explicitly provide a rounding mode:
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echo BigDecimal::of('1000.0')->dividedBy(3, RoundingMode::DOWN); // 333.3
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echo BigDecimal::of('1000.0')->dividedBy(3, RoundingMode::UP); // 333.4
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By default, the result has the same scale as the number, but you can also specify a different scale:
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echo BigDecimal::of(3)->dividedBy(11, RoundingMode::UP, 2); // 0.28
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echo BigDecimal::of(3)->dividedBy(11, RoundingMode::DOWN, 6); // 0.272727
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There are a number of rounding modes you can use:
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Rounding mode | Description
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-------------- | -----------
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`UNNECESSARY` | Assumes that no rounding is necessary, and throws an exception if it is.
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`UP` | Rounds away from zero.
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`DOWN` | Rounds towards zero.
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`CEILING` | Rounds towards positive infinity. If the result is positive, behaves as for `UP`; if negative, behaves as for `DOWN`.
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`FLOOR` | Rounds towards negative infinity. If the result is positive, behave as for `DOWN`; if negative, behave as for `UP`.
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`HALF_UP` | Rounds towards "nearest neighbor" unless both neighbors are equidistant, in which case round up. Behaves as for `UP` if the discarded fraction is >= 0.5; otherwise, behaves as for `DOWN`.
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`HALF_DOWN` | Rounds towards "nearest neighbor" unless both neighbors are equidistant, in which case round down. Behaves as for `UP` if the discarded fraction is > 0.5; otherwise, behaves as for `DOWN`.
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`HALF_CEILING` | Rounds towards "nearest neighbor" unless both neighbors are equidistant, in which case round towards positive infinity. If the result is positive, behaves as for `HALF_UP`; if negative, behaves as for `HALF_DOWN`.
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`HALF_FLOOR` | Rounds towards "nearest neighbor" unless both neighbors are equidistant, in which case round towards negative infinity. If the result is positive, behaves as for `HALF_DOWN`; if negative, behaves as for `HALF_UP`.
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`HALF_EVEN` | Rounds towards the "nearest neighbor" unless both neighbors are equidistant, in which case rounds towards the even neighbor. Behaves as for `HALF_UP` if the digit to the left of the discarded fraction is odd; behaves as for `HALF_DOWN` if it's even.
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#### BigRational
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The result of the division of a `BigRational` can always be represented exactly:
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echo BigRational::parse('123/456')->dividedBy('7'); // 123/3192
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echo BigRational::parse('123/456')->dividedBy('9/8'); // 984/4104
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### Serialization
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`BigInteger`, `BigDecimal` and `BigRational` can be safely serialized on a machine and unserialized on another,
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even if these machines do not share the same set of PHP extensions.
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For example, serializing on a machine with GMP support and unserializing on a machine that does not have this extension
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installed will still work as expected. |