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Add round_to_nearest/3 #199

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Add round_to_nearest/3 #199

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88ea6c7
round_to_nearest/3
chrisapa May 27, 2023
e4c8da7
Refactor variable
chrisapa May 27, 2023
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32 changes: 32 additions & 0 deletions lib/decimal.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -1061,6 +1061,38 @@ defmodule Decimal do
round(decimal(num), n, mode)
end

@doc """
Rounds the given number to the nearest number given as input with the given strategy
(default is to round to nearest one).

See `Decimal.Context` for more information about rounding algorithms.

## Examples

iex> Decimal.round_to_nearest("47.1", 5)
Decimal.new("45")

iex> Decimal.round_to_nearest("47.51", 5)
Decimal.new("50")

"""
@spec round_to_nearest(decimal, integer, rounding) :: t
def round_to_nearest(num, round_number, mode \\ :half_up)

def round_to_nearest(%Decimal{coef: :NaN} = num, _, _), do: num

def round_to_nearest(%Decimal{coef: :inf} = num, _, _), do: num

def round_to_nearest(%Decimal{} = num, round_number, mode) do
div(num, round_number)
|> round(0, mode)
|> mult(round_number)
end

def round_to_nearest(num, round_number, mode) do
round_to_nearest(decimal(num), round_number, mode)
end

@doc """
Finds the square root.

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117 changes: 117 additions & 0 deletions test/decimal_test.exs
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Expand Up @@ -742,6 +742,123 @@ defmodule DecimalTest do
assert roundneg.(~d"1099") == d(1, 11, 2)
end

test "round_to_nearest/3: special" do
assert Decimal.round_to_nearest(~d"inf", 5, :down) == d(1, :inf, 0)
assert Decimal.round_to_nearest(~d"nan", 5, :down) == d(1, :NaN, 0)
end

test "round_to_nearest/3: down" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :down)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 45, 0)
assert round_nearest.(~d"47.38") == d(1, 45, 0)
assert round_nearest.(~d"47.5") == d(1, 45, 0)
assert round_nearest.(~d"49.99") == d(1, 45, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 45, 0)
assert round_nearest.(~d"-47.38") == d(-1, 45, 0)
assert round_nearest.(~d"-47.5") == d(-1, 45, 0)
assert round_nearest.(~d"-49.99") == d(-1, 45, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: ceiling" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :ceiling)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 50, 0)
assert round_nearest.(~d"47.38") == d(1, 50, 0)
assert round_nearest.(~d"47.5") == d(1, 50, 0)
assert round_nearest.(~d"49.99") == d(1, 50, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 45, 0)
assert round_nearest.(~d"-47.38") == d(-1, 45, 0)
assert round_nearest.(~d"-47.5") == d(-1, 45, 0)
assert round_nearest.(~d"-49.99") == d(-1, 45, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: floor" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :floor)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 45, 0)
assert round_nearest.(~d"47.38") == d(1, 45, 0)
assert round_nearest.(~d"47.5") == d(1, 45, 0)
assert round_nearest.(~d"49.99") == d(1, 45, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 50, 0)
assert round_nearest.(~d"-47.38") == d(-1, 50, 0)
assert round_nearest.(~d"-47.5") == d(-1, 50, 0)
assert round_nearest.(~d"-49.99") == d(-1, 50, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: half up" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :half_up)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 45, 0)
assert round_nearest.(~d"47.38") == d(1, 45, 0)
assert round_nearest.(~d"47.5") == d(1, 50, 0)
assert round_nearest.(~d"49.99") == d(1, 50, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 45, 0)
assert round_nearest.(~d"-47.38") == d(-1, 45, 0)
assert round_nearest.(~d"-47.5") == d(-1, 50, 0)
assert round_nearest.(~d"-49.99") == d(-1, 50, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: half even" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :half_even)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 45, 0)
assert round_nearest.(~d"47.38") == d(1, 45, 0)
assert round_nearest.(~d"47.5") == d(1, 50, 0)
assert round_nearest.(~d"49.99") == d(1, 50, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 45, 0)
assert round_nearest.(~d"-47.38") == d(-1, 45, 0)
assert round_nearest.(~d"-47.5") == d(-1, 50, 0)
assert round_nearest.(~d"-49.99") == d(-1, 50, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: half down" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :half_down)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 45, 0)
assert round_nearest.(~d"47.38") == d(1, 45, 0)
assert round_nearest.(~d"47.5") == d(1, 45, 0)
assert round_nearest.(~d"49.99") == d(1, 50, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 45, 0)
assert round_nearest.(~d"-47.38") == d(-1, 45, 0)
assert round_nearest.(~d"-47.5") == d(-1, 45, 0)
assert round_nearest.(~d"-49.99") == d(-1, 50, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "round_to_nearest/3: up" do
round_nearest = &Decimal.round_to_nearest(&1, 5, :up)
assert round_nearest.(~d"45") == d(1, 45, 0)
assert round_nearest.(~d"46.35") == d(1, 50, 0)
assert round_nearest.(~d"47.38") == d(1, 50, 0)
assert round_nearest.(~d"47.5") == d(1, 50, 0)
assert round_nearest.(~d"49.99") == d(1, 50, 0)
assert round_nearest.(~d"50") == d(1, 50, 0)
assert round_nearest.(~d"-45") == d(-1, 45, 0)
assert round_nearest.(~d"-46.35") == d(-1, 50, 0)
assert round_nearest.(~d"-47.38") == d(-1, 50, 0)
assert round_nearest.(~d"-47.5") == d(-1, 50, 0)
assert round_nearest.(~d"-49.99") == d(-1, 50, 0)
assert round_nearest.(~d"-50") == d(-1, 50, 0)
end

test "sqrt/1" do
Context.with(%Context{precision: 9, rounding: :half_even}, fn ->
assert Decimal.sqrt(~d"0") == d(1, 0, 0)
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