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@ericmj
ericmj committed Dec 30, 2019
1 parent 93180b0 commit 1b6200d
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164 changes: 2 additions & 162 deletions lib/decimal.ex
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Original file line number Diff line number Diff line change
@@ -1,15 +1,3 @@
defmodule Decimal.Macros do
@moduledoc false

defmacro doc_since(version) do
if Version.match?(System.version(), ">= 1.7.0") do
quote do
@doc since: unquote(version)
end
end
end
end

defmodule Decimal do
@moduledoc """
Decimal arithmetic on arbitrary precision floating-point numbers.
Expand Down Expand Up @@ -63,6 +51,8 @@ defmodule Decimal do
import Bitwise
import Kernel, except: [abs: 1, div: 2, max: 2, min: 2, rem: 2, round: 1]
import Decimal.Macros
alias Decimal.Context
alias Decimal.Error

@power_of_2_to_52 4_503_599_627_370_496

Expand Down Expand Up @@ -130,156 +120,6 @@ defmodule Decimal do

defstruct sign: 1, coef: 0, exp: 0

defmodule Error do
@moduledoc """
The exception that all decimal operations may raise.
## Fields
* `signal` - the signalled error, additional signalled errors will be found
in the context.
* `reason` - the reason for the error.
* `result` - the result of the operation signalling the error.
Rescuing the error to access the result or the other fields of the error is
discouraged and should only be done for exceptional conditions. It is more
pragmatic to set the appropriate traps on the context and check the flags
after the operation if the result needs to be inspected.
"""

defexception [:message, :signal, :reason, :result]

def exception(opts) do
reason = if opts[:reason], do: ": " <> opts[:reason]
message = "#{opts[:signal]}#{reason}"

struct(__MODULE__, [message: message] ++ opts)
end
end

defmodule Context do
@moduledoc """
The context is kept in the process dictionary. It can be accessed with
`get/0` and `set/1`.
The default context has a precision of 28, the rounding algorithm is
`:half_up`. The set trap enablers are `:invalid_operation` and
`:division_by_zero`.
## Fields
* `precision` - maximum number of decimal digits in the coefficient. If an
operation result has more digits it will be rounded to `precision`
digits with the rounding algorithm in `rounding`.
* `rounding` - the rounding algorithm used when the coefficient's number of
exceeds `precision`. Strategies explained below.
* `flags` - a list of signals that for which the flag is sent. When an
exceptional condition is signalled its flag is set. The flags are sticky
and will be set until explicitly cleared.
* `traps` - a list of set trap enablers for signals. When a signal's trap
enabler is set the condition causes `Decimal.Error` to be raised.
## Rounding algorithms
* `:down` - round toward zero (truncate). Discarded digits are ignored,
result is unchanged.
* `:half_up` - if the discarded digits is greater than or equal to half of
the value of a one in the next left position then the coefficient will be
incremented by one (rounded up). Otherwise (the discarded digits are less
than half) the discarded digits will be ignored.
* `:half_even` - also known as "round to nearest" or "banker's rounding". If
the discarded digits is greater than half of the value of a one in the
next left position then the coefficient will be incremented by one
(rounded up). If they represent less than half discarded digits will be
ignored. Otherwise (exactly half), the coefficient is not altered if it's
even, or incremented by one (rounded up) if it's odd (to make an even
number).
* `:ceiling` - round toward +Infinity. If all of the discarded digits are
zero or the sign is negative the result is unchanged. Otherwise, the
coefficient will be incremented by one (rounded up).
* `:floor` - round toward -Infinity. If all of the discarded digits are zero
or the sign is positive the result is unchanged. Otherwise, the sign is
negative and coefficient will be incremented by one.
* `:half_down` - if the discarded digits is greater than half of the value
of a one in the next left position then the coefficient will be
incremented by one (rounded up). Otherwise (the discarded digits are half
or less) the discarded digits are ignored.
* `:up` - round away from zero. If all discarded digits are zero the
coefficient is not changed, otherwise it is incremented by one (rounded
up).
This table shows the results of rounding operations for all the rounding
algorithms:
Rounding algorithm | 5.5 | 2.5 | 1.6 | 1.1 | 1.0 | -1.0 | -1.1 | -1.6 | -2.5 | -5.5
:----------------- | :-- | :-- | :-- | :-- | :-- | :--- | :--- | :--- | :--- | :---
`:up` | 6 | 3 | 2 | 2 | 1 | -1 | -2 | -2 | -3 | -6
`:down` | 5 | 2 | 1 | 1 | 1 | -1 | -1 | -1 | -2 | -5
`:ceiling` | 6 | 3 | 2 | 2 | 1 | -1 | -1 | -1 | -2 | -5
`:floor` | 5 | 2 | 1 | 1 | 1 | -1 | -2 | -2 | -3 | -6
`:half_up` | 6 | 3 | 2 | 1 | 1 | -1 | -1 | -2 | -3 | -6
`:half_down` | 5 | 2 | 2 | 1 | 1 | -1 | -1 | -2 | -2 | -5
`:half_even` | 6 | 2 | 2 | 1 | 1 | -1 | -1 | -2 | -2 | -6
"""
@type t :: %__MODULE__{
precision: pos_integer,
rounding: Decimal.rounding(),
flags: [Decimal.signal()],
traps: [Decimal.signal()]
}

defstruct precision: 28,
rounding: :half_up,
flags: [],
traps: [:invalid_operation, :division_by_zero]

@context_key :"$decimal_context"

@doc """
Runs function with given context.
"""
doc_since("1.9.0")
@spec with(t(), (() -> x)) :: x when x: var
def with(%Context{} = context, fun) when is_function(fun, 0) do
old = Process.put(@context_key, context)

try do
fun.()
after
set(old || %Context{})
end
end

@doc """
Gets the process' context.
"""
doc_since("1.9.0")
@spec get() :: t()
def get() do
Process.get(@context_key, %Context{})
end

@doc """
Set the process' context.
"""
doc_since("1.9.0")
@spec set(t()) :: :ok
def set(%Context{} = context) do
Process.put(@context_key, context)
:ok
end

@doc """
Update the process' context.
"""
doc_since("1.9.0")
@spec update((t() -> t())) :: :ok
def update(fun) when is_function(fun, 1) do
get() |> fun.() |> set()
end
end

defmacrop error(flags, reason, result, context \\ nil) do
quote bind_quoted: binding() do
case handle_error(flags, reason, result, context) do
Expand Down
125 changes: 125 additions & 0 deletions lib/decimal/context.ex
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Original file line number Diff line number Diff line change
@@ -0,0 +1,125 @@
defmodule Decimal.Context do
import Decimal.Macros
alias Decimal.Context

@moduledoc """
The context is kept in the process dictionary. It can be accessed with
`get/0` and `set/1`.
The default context has a precision of 28, the rounding algorithm is
`:half_up`. The set trap enablers are `:invalid_operation` and
`:division_by_zero`.
## Fields
* `precision` - maximum number of decimal digits in the coefficient. If an
operation result has more digits it will be rounded to `precision`
digits with the rounding algorithm in `rounding`.
* `rounding` - the rounding algorithm used when the coefficient's number of
exceeds `precision`. Strategies explained below.
* `flags` - a list of signals that for which the flag is sent. When an
exceptional condition is signalled its flag is set. The flags are sticky
and will be set until explicitly cleared.
* `traps` - a list of set trap enablers for signals. When a signal's trap
enabler is set the condition causes `Decimal.Error` to be raised.
## Rounding algorithms
* `:down` - round toward zero (truncate). Discarded digits are ignored,
result is unchanged.
* `:half_up` - if the discarded digits is greater than or equal to half of
the value of a one in the next left position then the coefficient will be
incremented by one (rounded up). Otherwise (the discarded digits are less
than half) the discarded digits will be ignored.
* `:half_even` - also known as "round to nearest" or "banker's rounding". If
the discarded digits is greater than half of the value of a one in the
next left position then the coefficient will be incremented by one
(rounded up). If they represent less than half discarded digits will be
ignored. Otherwise (exactly half), the coefficient is not altered if it's
even, or incremented by one (rounded up) if it's odd (to make an even
number).
* `:ceiling` - round toward +Infinity. If all of the discarded digits are
zero or the sign is negative the result is unchanged. Otherwise, the
coefficient will be incremented by one (rounded up).
* `:floor` - round toward -Infinity. If all of the discarded digits are zero
or the sign is positive the result is unchanged. Otherwise, the sign is
negative and coefficient will be incremented by one.
* `:half_down` - if the discarded digits is greater than half of the value
of a one in the next left position then the coefficient will be
incremented by one (rounded up). Otherwise (the discarded digits are half
or less) the discarded digits are ignored.
* `:up` - round away from zero. If all discarded digits are zero the
coefficient is not changed, otherwise it is incremented by one (rounded
up).
This table shows the results of rounding operations for all the rounding
algorithms:
Rounding algorithm | 5.5 | 2.5 | 1.6 | 1.1 | 1.0 | -1.0 | -1.1 | -1.6 | -2.5 | -5.5
:----------------- | :-- | :-- | :-- | :-- | :-- | :--- | :--- | :--- | :--- | :---
`:up` | 6 | 3 | 2 | 2 | 1 | -1 | -2 | -2 | -3 | -6
`:down` | 5 | 2 | 1 | 1 | 1 | -1 | -1 | -1 | -2 | -5
`:ceiling` | 6 | 3 | 2 | 2 | 1 | -1 | -1 | -1 | -2 | -5
`:floor` | 5 | 2 | 1 | 1 | 1 | -1 | -2 | -2 | -3 | -6
`:half_up` | 6 | 3 | 2 | 1 | 1 | -1 | -1 | -2 | -3 | -6
`:half_down` | 5 | 2 | 2 | 1 | 1 | -1 | -1 | -2 | -2 | -5
`:half_even` | 6 | 2 | 2 | 1 | 1 | -1 | -1 | -2 | -2 | -6
"""
@type t :: %__MODULE__{
precision: pos_integer,
rounding: Decimal.rounding(),
flags: [Decimal.signal()],
traps: [Decimal.signal()]
}

defstruct precision: 28,
rounding: :half_up,
flags: [],
traps: [:invalid_operation, :division_by_zero]

@context_key :"$decimal_context"

@doc """
Runs function with given context.
"""
doc_since("1.9.0")
@spec with(t(), (() -> x)) :: x when x: var
def with(%Context{} = context, fun) when is_function(fun, 0) do
old = Process.put(@context_key, context)

try do
fun.()
after
set(old || %Context{})
end
end

@doc """
Gets the process' context.
"""
doc_since("1.9.0")
@spec get() :: t()
def get() do
Process.get(@context_key, %Context{})
end

@doc """
Set the process' context.
"""
doc_since("1.9.0")
@spec set(t()) :: :ok
def set(%Context{} = context) do
Process.put(@context_key, context)
:ok
end

@doc """
Update the process' context.
"""
doc_since("1.9.0")
@spec update((t() -> t())) :: :ok
def update(fun) when is_function(fun, 1) do
get() |> fun.() |> set()
end
end
26 changes: 26 additions & 0 deletions lib/decimal/error.ex
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Original file line number Diff line number Diff line change
@@ -0,0 +1,26 @@
defmodule Decimal.Error do
@moduledoc """
The exception that all decimal operations may raise.
## Fields
* `signal` - the signalled error, additional signalled errors will be found
in the context.
* `reason` - the reason for the error.
* `result` - the result of the operation signalling the error.
Rescuing the error to access the result or the other fields of the error is
discouraged and should only be done for exceptional conditions. It is more
pragmatic to set the appropriate traps on the context and check the flags
after the operation if the result needs to be inspected.
"""

defexception [:message, :signal, :reason, :result]

def exception(opts) do
reason = if opts[:reason], do: ": " <> opts[:reason]
message = "#{opts[:signal]}#{reason}"

struct(__MODULE__, [message: message] ++ opts)
end
end
11 changes: 11 additions & 0 deletions lib/decimal/macros.ex
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
defmodule Decimal.Macros do
@moduledoc false

defmacro doc_since(version) do
if Version.match?(System.version(), ">= 1.7.0") do
quote do
@doc since: unquote(version)
end
end
end
end
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