A small, fast Javascript library for arbitrary-precision decimal arithmetic.

The little sister to bignumber.js.

• Faster, smaller and easier-to-use than Javascript versions of Java's BigDecimal
• Only 2.5 KB minified and gzipped
• Simple API
• Replicates the toExponential, toFixed and toPrecision methods of Javascript's Number type
• Includes a sqrt method
• Stores values in an accessible decimal floating point format
• No dependencies
• Comprehensive documentation and test set

The library is the single Javascript file big.js
(or big.min.js, which is big.js minified using uglify-js).

It can be loaded via a script tag in an HTML document for the browser

<script src='./relative/path/to/big.js'></script>

or as a CommonJS, Node.js or AMD module using require.

For Node, put the big.js file into the same directory as the file that is requiring it and use

var Big = require('./big'); 

or put it in a node_modules directory within the directory and use require('big').

To load with AMD loader libraries such as requireJS:

require(['big'], function(Big) {  
    // Use Big here in local scope. No global Big. 
});

In all examples below, var, semicolons and toString calls are not shown.
If a commented-out value is in quotes it means toString has been called on the preceding expression.

The library exports a single function: Big, the constructor of Big number instances.
It accepts a value of type Number, String or Big number Object.

x = new Big(123.4567)
y = Big('123456.7e-3')        // 'new' is optional
z = new Big(x)
y.cmp(z) == 0                 // true

A Big number is immutable in the sense that it is not changed by its methods.

0.3 - 0.1                     // 0.19999999999999998  
x = new Big(0.3)            
x.minus(0.1)                  // "0.2"
x                             // "0.3"

The methods that return a Big number can be chained.

x.div(y).plus(z).times(9).minus('1.234567801234567e+8').plus(976.54321).div('2598.11772')   
x.sqrt().div(y).pow(3).cmp(y.mod(z)) == 1      // true

Like Javascript's Number type, there are toExponential, toFixed and toPrecision methods.

x = new Big(255.5)        
x.toExponential(5)             // "2.55500e+2"
x.toFixed(5)                   // "255.50000"
x.toPrecision(5)               // "255.50"

The maximum number of decimal places and the rounding mode used to round the results of the div, sqrt and pow (with negative exponent) methods is determined by the value of the DP and RM properties of the Big number constructor.
The other methods always give the exact result.

Big.DP = 10
Big.RM = 1

x = new Big(2);
y = new Big(3);        
z = x.div(y)                 // "0.6666666667"
z.sqrt()                     // "0.8164965809"
z.pow(-3)                    // "3.3749999995"
z.times(z)                   // "0.44444444448888888889"
z.times(z).round(10)         // "0.4444444445"

The value of a Big number is stored in a decimal floating point format in terms of a coefficient, exponent and sign.

x = new Big(-123.456); 
x.c                          // "1,2,3,4,5,6"    coefficient (i.e. significand)
x.e                          // 2                exponent 
x.s                          // -1               sign

For futher information see the API reference in the doc folder.

The test directory contains the test scripts for each Big number method.

The tests can be run with Node or a browser.

To test a single method, from a command-line shell at the test/ directory, use e.g.

$ node toFixed

To test all the methods

$ node every-test

For the browser, see single-test.html and every-test.html in the test/browser/ directory.
big-vs-number.html enables some of the methods of big.js to be compared with those of Javascript's Number type.

The perf directory contains two applications and a lib directory containing the BigDecimal libraries used by both.

big-vs-bigdecimal.html tests the performance of big.js against the Javascript translations of two versions of BigDecimal, its use should be more or less self-explanatory. (The GWT version doesn't work in IE 6.)

• GWT: java.math.BigDecimal
  https://github.com/iriscouch/bigdecimal.js
• ICU4J: com.ibm.icu.math.BigDecimal
  https://github.com/dtrebbien/BigDecimal.js

The BigDecimal in Node's npm registry is the GWT version. Despite its seeming popularity I have found it to have some serious bugs, see the Node script perf/lib/bigdecimal_GWT/bugs.js for examples of flaws in its remainder, divide and compareTo methods.

bigtime.js is a Node command-line application which tests the performance of big.js against the GWT version of BigDecimal from the npm registry.

For example, to compare the time taken by the big.js plus method and the BigDecimal add method:

$ node bigtime plus 10000 40      

This will time 10000 calls to each, using operands of up to 40 random digits and will check that the results match.

For help:

$ node bigtime -h

I.e. minify.

For Node, if uglify-js is installed globally ( npm install uglify-js -g ) then

uglifyjs -o ./big.min.js ./big.js

will create big.min.js.

Bugs/issues/comments to:

Michael Mclaughlin
[email protected]

Bitcoin donation to:
1LS9yszMtSB6GkhHmB9yQoivTnry2m8QFJ
Thank you

See LICENCE.

1.0.0

• 7/11/2012 Initial release

1.0.1

• Changed default value of MAX_DP to 1E6