mirror of https://github.com/jkjoy/sunpeiwen.git
247 lines
8.4 KiB
Markdown
247 lines
8.4 KiB
Markdown
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An arbitrary-precision Decimal type for JavaScript.
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[](https://www.npmjs.com/package/decimal.js)
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[](https://www.npmjs.com/package/decimal.js)
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[](https://travis-ci.org/MikeMcl/decimal.js)
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[](https://cdnjs.com/libraries/decimal.js)
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<br>
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## Features
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- Integers and floats
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- Simple but full-featured API
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- Replicates many of the methods of JavaScript's `Number.prototype` and `Math` objects
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- Also handles hexadecimal, binary and octal values
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- Faster, smaller, and perhaps easier to use than JavaScript versions of Java's BigDecimal
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- No dependencies
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- Wide platform compatibility: uses JavaScript 1.5 (ECMAScript 3) features only
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- Comprehensive [documentation](https://mikemcl.github.io/decimal.js/) and test set
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- Used under the hood by [math.js](https://github.com/josdejong/mathjs)
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- Includes a TypeScript declaration file: *decimal.d.ts*
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The library is similar to [bignumber.js](https://github.com/MikeMcl/bignumber.js/), but here
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precision is specified in terms of significant digits rather than decimal places, and all
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calculations are rounded to the precision (similar to Python's decimal module) rather than just
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those involving division.
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This library also adds the trigonometric functions, among others, and supports non-integer powers,
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which makes it a significantly larger library than *bignumber.js* and the even smaller
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[big.js](https://github.com/MikeMcl/big.js/).
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For a lighter version of this library without the trigonometric functions see
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[decimal.js-light](https://github.com/MikeMcl/decimal.js-light/).
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## Load
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The library is the single JavaScript file *decimal.js* or ES module *decimal.mjs*.
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Browser:
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```html
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<script src='path/to/decimal.js'></script>
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<script type="module">
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import Decimal from './path/to/decimal.mjs';
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...
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</script>
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```
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[Node.js](https://nodejs.org):
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```bash
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npm install decimal.js
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```
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```js
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const Decimal = require('decimal.js');
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import Decimal from 'decimal.js';
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import {Decimal} from 'decimal.js';
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```
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## Use
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*In all examples below, semicolons and `toString` calls are not shown.
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If a commented-out value is in quotes it means `toString` has been called on the preceding expression.*
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The library exports a single constructor function, `Decimal`, which expects a single argument that is a number, string or Decimal instance.
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```js
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x = new Decimal(123.4567)
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y = new Decimal('123456.7e-3')
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z = new Decimal(x)
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x.equals(y) && y.equals(z) && x.equals(z) // true
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```
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If using values with more than a few digits, it is recommended to pass strings rather than numbers to avoid a potential loss of precision.
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```js
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// Precision loss from using numeric literals with more than 15 significant digits.
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new Decimal(1.0000000000000001) // '1'
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new Decimal(88259496234518.57) // '88259496234518.56'
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new Decimal(99999999999999999999) // '100000000000000000000'
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// Precision loss from using numeric literals outside the range of Number values.
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new Decimal(2e+308) // 'Infinity'
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new Decimal(1e-324) // '0'
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// Precision loss from the unexpected result of arithmetic with Number values.
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new Decimal(0.7 + 0.1) // '0.7999999999999999'
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```
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As with JavaScript numbers, strings can contain underscores as separators to improve readability.
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```js
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x = new Decimal('2_147_483_647')
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```
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String values in binary, hexadecimal or octal notation are also accepted if the appropriate prefix is included.
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```js
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x = new Decimal('0xff.f') // '255.9375'
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y = new Decimal('0b10101100') // '172'
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z = x.plus(y) // '427.9375'
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z.toBinary() // '0b110101011.1111'
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z.toBinary(13) // '0b1.101010111111p+8'
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// Using binary exponential notation to create a Decimal with the value of `Number.MAX_VALUE`.
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x = new Decimal('0b1.1111111111111111111111111111111111111111111111111111p+1023')
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// '1.7976931348623157081e+308'
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```
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Decimal instances are immutable in the sense that they are not changed by their methods.
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```js
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0.3 - 0.1 // 0.19999999999999998
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x = new Decimal(0.3)
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x.minus(0.1) // '0.2'
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x // '0.3'
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```
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The methods that return a Decimal can be chained.
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```js
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x.dividedBy(y).plus(z).times(9).floor()
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x.times('1.23456780123456789e+9').plus(9876.5432321).dividedBy('4444562598.111772').ceil()
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```
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Many method names have a shorter alias.
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```js
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x.squareRoot().dividedBy(y).toPower(3).equals(x.sqrt().div(y).pow(3)) // true
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x.comparedTo(y.modulo(z).negated() === x.cmp(y.mod(z).neg()) // true
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```
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Most of the methods of JavaScript's `Number.prototype` and `Math` objects are replicated.
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```js
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x = new Decimal(255.5)
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x.toExponential(5) // '2.55500e+2'
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x.toFixed(5) // '255.50000'
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x.toPrecision(5) // '255.50'
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Decimal.sqrt('6.98372465832e+9823') // '8.3568682281821340204e+4911'
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Decimal.pow(2, 0.0979843) // '1.0702770511687781839'
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// Using `toFixed()` to avoid exponential notation:
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x = new Decimal('0.0000001')
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x.toString() // '1e-7'
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x.toFixed() // '0.0000001'
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```
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And there are `isNaN` and `isFinite` methods, as `NaN` and `Infinity` are valid `Decimal` values.
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```js
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x = new Decimal(NaN) // 'NaN'
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y = new Decimal(Infinity) // 'Infinity'
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x.isNaN() && !y.isNaN() && !x.isFinite() && !y.isFinite() // true
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```
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There is also a `toFraction` method with an optional *maximum denominator* argument.
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```js
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z = new Decimal(355)
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pi = z.dividedBy(113) // '3.1415929204'
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pi.toFraction() // [ '7853982301', '2500000000' ]
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pi.toFraction(1000) // [ '355', '113' ]
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```
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All calculations are rounded according to the number of significant digits and rounding mode specified
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by the `precision` and `rounding` properties of the Decimal constructor.
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For advanced usage, multiple Decimal constructors can be created, each with their own independent
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configuration which applies to all Decimal numbers created from it.
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```js
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// Set the precision and rounding of the default Decimal constructor
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Decimal.set({ precision: 5, rounding: 4 })
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// Create another Decimal constructor, optionally passing in a configuration object
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Dec = Decimal.clone({ precision: 9, rounding: 1 })
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x = new Decimal(5)
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y = new Dec(5)
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x.div(3) // '1.6667'
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y.div(3) // '1.66666666'
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```
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The value of a Decimal is stored in a floating point format in terms of its digits, exponent and sign, but these properties should be considered read-only.
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```js
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x = new Decimal(-12345.67);
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x.d // [ 12345, 6700000 ] digits (base 10000000)
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x.e // 4 exponent (base 10)
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x.s // -1 sign
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```
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For further information see the [API](http://mikemcl.github.io/decimal.js/) reference in the *doc* directory.
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## Test
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To run the tests using Node.js from the root directory:
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```bash
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npm test
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```
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Each separate test module can also be executed individually, for example:
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```bash
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node test/modules/toFraction
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```
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To run the tests in a browser, open *test/test.html*.
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## Minify
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Two minification examples:
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Using [uglify-js](https://github.com/mishoo/UglifyJS) to minify the *decimal.js* file:
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```bash
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npm install uglify-js -g
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uglifyjs decimal.js --source-map url=decimal.min.js.map -c -m -o decimal.min.js
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```
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Using [terser](https://github.com/terser/terser) to minify the ES module version, *decimal.mjs*:
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```bash
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npm install terser -g
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terser decimal.mjs --source-map url=decimal.min.mjs.map -c -m --toplevel -o decimal.min.mjs
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```
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```js
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import Decimal from './decimal.min.mjs';
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```
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## Licence
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[The MIT Licence (Expat).](LICENCE.md)
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