Decimal
Arbitrary precision decimal arithmetic for Elixir.
Documentation: http://ericmj.github.io/decimal
Usage
Add Decimal as a dependency in your mix.exs file.
elixir
def deps do
[ { :decimal, "~> 0.2.4" } ]
end
After you are done, run mix deps.get in your shell to fetch and compile Decimal. Start an interactive Elixir shell with iex -S mix.
```iex iex> alias Decimal, as: D nil iex> D.add(D.new(6), D.new(7))
Decimal<13>
iex> D.div(D.new(1), D.new(3))
Decimal<0.333333333>
```
Examples
Using the context
The context specifies the maximum precision of the result of calculations and the rounding algorithm if the result has a higher precision than the specified maximum. It also holds the list of set of trap enablers and the currently set flags.
The context is stored in the process dictionary, this means that you don't have to pass the context around explicitly and the flags will be updated automatically.
The context is accessed with Decimal.get_context/0 and set with
Decimal.set_context/1. It can also be temporarily set with
Decimal.with_context/2.
iex
iex> D.get_context
Decimal.Context[precision: 9, rounding: :half_up, flags: [],
traps: [:invalid_operation, :division_by_zero]]
iex> D.with_context Context[precision: 2], fn -> IO.inspect D.get_context end
Decimal.Context[precision: 2, rounding: :half_up, flags: [],
traps: [:invalid_operation, :division_by_zero]]
:ok
iex> D.set_context(D.get_context.traps([]))
:ok
iex> Decimal.get_context
Decimal.Context[precision: 9, rounding: :half_up, flags: [], traps: []]
Precision and rounding
The precision is used to limit the amount of decimal digits in the coefficient:
```iex iex> D.setcontext(D.getcontext.precision(9)) :ok iex> D.div(D.new(1), D.new(3))
Decimal<0.333333333>
iex> D.setcontext(D.getcontext.precision(2)) :ok iex> D.div(D.new(1), D.new(3))
Decimal<0.33>
```
The rounding algorithm specifies how the result of an operation shall be rounded when it get be represented with the current precision:
```iex iex> D.setcontext(D.getcontext.rounding(:half_up)) :ok iex> D.div(D.new(31), D.new(2))
Decimal<16>
iex> D.setcontext(D.getcontext.rounding(:floor)) :ok iex> D.div(D.new(31), D.new(2))
Decimal<15>
```
Flags and trap enablers
When an exceptional condition is signalled its flag is set in the context and if
if the trap enabler is set Decimal.Error will be raised.
```iex iex> D.getcontext.traps [:invalidoperation, :divisionbyzero] iex> D.get_context.flags [] iex> D.div(D.new(31), D.new(2))
Decimal<15>
iex> D.get_context.flags [:inexact, :rounded] ```
:inexact and :rounded were signalled above because the result of the
operation was inexact given the context's precision and had to be rounded to fit
the precision. Decimal.Error was not raised because the signals' trap enablers
weren't set. We can, however, set the trap enabler if we what this condition to
raise.
iex
iex> D.set_context(D.get_context.update_traps((&1 ++ [:inexact]))
:ok
iex> D.div(D.new(31), D.new(2))
** (Decimal.Error)
The default trap enablers, such as :division_by_zero can be unset:
```iex iex> D.getcontext.traps [:invalidoperation, :divisionbyzero] iex> D.div(D.new(42), D.new(0)) ** (Decimal.Error) iex> D.setcontext(D.getcontext.traps([]).flags([])) :ok iex> D.div(D.new(42), D.new(0))
Decimal
iex> D.getcontext.flags [:divisionby_zero] ```
Mitigating rounding errors
TODO
License
Copyright 2013 Eric Meadows-Jönsson
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.