A small library for arbitrary-precision decimal arithmetic inspired by big.js

Coverage Status build style: dart lint recommended License: MIT


  • Simple API
  • Easier-to-use
  • Replicates the toStringAsExponential, toStringAsFixed and toStringAsPrecision methods of Dart Numbers
  • Stores values in an accessible decimal floating point format
  • Comprehensive documentation and test set
  • Uses only Dart, so works in well where Dart work


In the code examples below, semicolons and toString calls are not shown.

The library exports a some Extensions for String, double, int, Big.

A Big number is created from a primitive number, String, or other Big number.

var x = Big(123.4567)
var y = Big('123456.7e-3')
var z = Big(x)
x.eq(y) && x.eq(z) && y.eq(z)          // true

In Big strict mode, creating a Big number from a primitive number is disallowed.

Big.strict = true
x = Big(1)                         // BigError(code: BigErrorCode.invalidNumber)
y = Big('1.0000000000000001')
y.toNumber()                       // BigError(code: BigErrorCode.impreciseConversion)

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

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

The methods that return a Big number can be chained.

x.sqrt().div(y).pow(3).gt(y.mod(z))    // true

Like JavaScript's Number type, there are toStringAsExponential, toStringAsFixed and toStringAsPrecision methods.

x = Big(255.5)
x.toStringAsExponential(5)                     // "2.55500e+2"
x.toStringAsFixed(5)                           // "255.50000"
x.toStringAsPrecision(5)                       // "255.50"

The arithmetic methods always return the exact result except div, sqrt and pow (with negative exponent), as these methods involve division.

The maximum number of decimal places and the rounding mode used to round the results of these methods is determined by the value of the dp and rm properties of the Big number constructor.

Big.dp = 10
Big.rm = RoundingMode.roundHalfUp
x = Big(2);
y = 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 = Big(-123.456);
x.c                                    // [1,2,3,4,5,6]    coefficient (i.e. significand)
x.e                                    // 2                exponent
x.s                                    // -1               sign


A small library for arbitrary-precision decimal arithmetic inspired by big.js