234 lines
6.5 KiB
Elixir
234 lines
6.5 KiB
Elixir
import Kernel, except: [round: 1]
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defmodule Float do
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@moduledoc """
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Functions for working with floating point numbers.
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"""
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@doc """
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Parses a binary into a float.
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If successful, returns a tuple in the form of `{float, remainder_of_binary}`;
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when the binary cannot be coerced into a valid float, the atom `:error` is
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returned.
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If the size of float exceeds the maximum size of `1.7976931348623157e+308`,
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the `ArgumentError` exception is raised.
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If you want to convert a string-formatted float directly to a float,
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`String.to_float/1` can be used instead.
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## Examples
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iex> Float.parse("34")
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{34.0, ""}
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iex> Float.parse("34.25")
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{34.25, ""}
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iex> Float.parse("56.5xyz")
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{56.5, "xyz"}
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iex> Float.parse("pi")
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:error
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"""
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@spec parse(binary) :: {float, binary} | :error
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def parse("-" <> binary) do
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case parse_unsigned(binary) do
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:error -> :error
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{number, remainder} -> {-number, remainder}
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end
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end
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def parse("+" <> binary) do
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parse_unsigned(binary)
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end
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def parse(binary) do
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parse_unsigned(binary)
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end
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defp parse_unsigned(<<digit, rest::binary>>) when digit in ?0..?9, do:
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parse_unsigned(rest, false, false, <<digit>>)
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defp parse_unsigned(binary) when is_binary(binary), do:
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:error
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defp parse_unsigned(<<digit, rest::binary>>, dot?, e?, acc) when digit in ?0..?9, do:
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parse_unsigned(rest, dot?, e?, <<acc::binary, digit>>)
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defp parse_unsigned(<<?., digit, rest::binary>>, false, false, acc) when digit in ?0..?9, do:
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parse_unsigned(rest, true, false, <<acc::binary, ?., digit>>)
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defp parse_unsigned(<<exp_marker, digit, rest::binary>>, dot?, false, acc) when exp_marker in 'eE' and digit in ?0..?9, do:
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parse_unsigned(rest, true, true, <<add_dot(acc, dot?)::binary, ?e, digit>>)
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defp parse_unsigned(<<exp_marker, sign, digit, rest::binary>>, dot?, false, acc) when exp_marker in 'eE' and sign in '-+' and digit in ?0..?9, do:
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parse_unsigned(rest, true, true, <<add_dot(acc, dot?)::binary, ?e, sign, digit>>)
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defp parse_unsigned(rest, dot?, _e?, acc), do:
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{:erlang.binary_to_float(add_dot(acc, dot?)), rest}
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defp add_dot(acc, true), do: acc
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defp add_dot(acc, false), do: acc <> ".0"
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@doc """
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Rounds a float to the largest integer less than or equal to `num`.
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`floor/2` also accepts a precision to round a floating point value down
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to an arbitrary number of fractional digits (between 0 and 15).
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This function always returns a float. `Kernel.trunc/1` may be used instead to
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truncate the result to an integer afterwards.
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## Examples
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iex> Float.floor(34.25)
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34.0
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iex> Float.floor(-56.5)
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-57.0
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iex> Float.floor(34.259, 2)
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34.25
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"""
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@spec floor(float, 0..15) :: float
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def floor(number, precision \\ 0) when is_float(number) and precision in 0..15 do
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power = power_of_10(precision)
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number = number * power
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truncated = trunc(number)
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variance = if number - truncated < 0, do: -1.0, else: 0.0
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(truncated + variance) / power
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end
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@doc """
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Rounds a float to the smallest integer greater than or equal to `num`.
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`ceil/2` also accepts a precision to round a floating point value down
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to an arbitrary number of fractional digits (between 0 and 15).
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This function always returns floats. `Kernel.trunc/1` may be used instead to
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truncate the result to an integer afterwards.
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## Examples
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iex> Float.ceil(34.25)
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35.0
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iex> Float.ceil(-56.5)
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-56.0
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iex> Float.ceil(34.251, 2)
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34.26
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"""
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@spec ceil(float, 0..15) :: float
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def ceil(number, precision \\ 0) when is_float(number) and precision in 0..15 do
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power = power_of_10(precision)
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number = number * power
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truncated = trunc(number)
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variance = if number - truncated > 0, do: 1.0, else: 0.0
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(truncated + variance) / power
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end
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@doc """
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Rounds a floating point value to an arbitrary number of fractional digits
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(between 0 and 15).
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This function only accepts floats and always returns a float. Use
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`Kernel.round/1` if you want a function that accepts both floats and integers
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and always returns an integer.
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## Examples
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iex> Float.round(5.5674, 3)
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5.567
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iex> Float.round(5.5675, 3)
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5.568
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iex> Float.round(-5.5674, 3)
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-5.567
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iex> Float.round(-5.5675, 3)
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-5.568
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iex> Float.round(-5.5675)
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-6.0
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"""
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@spec round(float, 0..15) :: float
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def round(number, precision \\ 0) when is_float(number) and precision in 0..15 do
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power = power_of_10(precision)
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Kernel.round(number * power) / power
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end
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Enum.reduce 0..15, 1, fn x, acc ->
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defp power_of_10(unquote(x)), do: unquote(acc)
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acc * 10
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end
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@doc """
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Returns a charlist which corresponds to the text representation
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of the given float.
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It uses the shortest representation according to algorithm described
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in "Printing Floating-Point Numbers Quickly and Accurately" in
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Proceedings of the SIGPLAN '96 Conference on Programming Language
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Design and Implementation.
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## Examples
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iex> Float.to_charlist(7.0)
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'7.0'
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"""
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@spec to_charlist(float) :: charlist
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def to_charlist(float) when is_float(float) do
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:io_lib_format.fwrite_g(float)
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end
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@doc """
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Returns a binary which corresponds to the text representation
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of the given float.
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It uses the shortest representation according to algorithm described
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in "Printing Floating-Point Numbers Quickly and Accurately" in
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Proceedings of the SIGPLAN '96 Conference on Programming Language
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Design and Implementation.
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## Examples
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iex> Float.to_string(7.0)
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"7.0"
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"""
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@spec to_string(float) :: String.t
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def to_string(float) when is_float(float) do
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IO.iodata_to_binary(:io_lib_format.fwrite_g(float))
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end
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# TODO: Deprecate by v1.5
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@doc false
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def to_char_list(float), do: Float.to_charlist(float)
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@doc false
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def to_char_list(float, options) do
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IO.warn "Float.to_char_list/2 is deprecated, use :erlang.float_to_list/2 instead"
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:erlang.float_to_list(float, expand_compact(options))
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end
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@doc false
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def to_string(float, options) do
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IO.warn "Float.to_string/2 is deprecated, use :erlang.float_to_binary/2 instead"
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:erlang.float_to_binary(float, expand_compact(options))
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end
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defp expand_compact([{:compact, false} | t]), do: expand_compact(t)
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defp expand_compact([{:compact, true} | t]), do: [:compact | expand_compact(t)]
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defp expand_compact([h | t]), do: [h | expand_compact(t)]
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defp expand_compact([]), do: []
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end
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