factor out float formatting into nicedecimal, include as dep
This commit is contained in:
alisdair sullivan
parent
ed33626ed5
commit
620e6c7d91
4 changed files with 9 additions and 171 deletions
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@ -139,7 +139,7 @@ encode(literal, Literal, _Opts) ->
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encode(integer, Integer, _Opts) ->
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erlang:integer_to_list(Integer);
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encode(float, Float, _Opts) ->
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jsx_utils:nice_decimal(Float).
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nicedecimal:format(Float).
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space(Opts) ->
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@ -24,7 +24,6 @@
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-module(jsx_utils).
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-export([parse_opts/1]).
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-export([nice_decimal/1]).
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-export([json_escape/2]).
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-include("../include/jsx_opts.hrl").
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@ -49,137 +48,6 @@ parse_opts(_, _) ->
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{error, badarg}.
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%% conversion of floats to 'nice' decimal output. erlang's float implementation
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%% is almost but not quite ieee 754. it converts negative zero to plain zero
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%% silently, and throws exceptions for any operations that would produce NaN
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%% or infinity. as far as I can tell that is. trying to match against NaN or
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%% infinity binary patterns produces nomatch exceptions, and arithmetic
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%% operations produce badarg exceptions. with that in mind, this function
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%% makes no attempt to handle special values (except for zero)
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%% algorithm from "Printing Floating-Point Numbers Quickly and Accurately" by
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%% Burger & Dybvig
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-spec nice_decimal(Float::float()) -> string().
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nice_decimal(0.0) -> "0.0";
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nice_decimal(Num) ->
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{F, E} = extract(<<Num:64/float>>),
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{R, S, MP, MM} = initial_vals(F, E),
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K = ceiling((math:log(abs(Num)) / math:log(10)) - 1.0e-10),
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Round = F band 1 =:= 0,
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{Dpoint, Digits} = scale(R, S, MP, MM, K, 10, Round),
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if Num >= 0 -> digits_to_list(Dpoint, Digits)
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; Num < 0 -> "-" ++ digits_to_list(Dpoint, Digits)
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end.
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%% internal functions
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extract(<<_:1, 0:11, Frac:52>>) -> {Frac, -1074};
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extract(<<_:1, Exp:11, Frac:52>>) -> {Frac + (1 bsl 52), Exp - 1075}.
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initial_vals(F, E) when E >= 0, F /= 1 bsl 52 ->
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BE = 1 bsl E,
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{F * BE * 2, 2, BE, BE};
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initial_vals(F, E) when E >= 0 ->
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BE = 1 bsl E,
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{F * BE * 4, 4, BE * 2, BE};
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initial_vals(F, E) when E == -1074; F /= 1 bsl 52 ->
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{F * 2, 1 bsl (-E + 1), 1, 1};
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initial_vals(F, E) ->
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{F * 4, 1 bsl (-E + 2), 2, 1}.
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ceiling(X) ->
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Y = erlang:trunc(X),
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case X - Y of
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Z when Z > 0 -> Y + 1
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; _ -> Y
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end.
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scale(R, S, MP, MM, K, B, Round) ->
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case K >= 0 of
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true -> fixup(R, S * pow(B, K), MP, MM, K, B, Round)
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; false ->
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Scale = pow(B, -1 * K),
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fixup(R * Scale, S, MP * Scale, MM * Scale, K, B, Round)
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end.
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fixup(R, S, MP, MM, K, B, true) ->
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case (R + MP >= S) of
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true -> {K + 1, generate(R, S, MP, MM, B, true)}
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; false -> {K, generate(R * B, S, MP * B, MM * B, B, true)}
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end;
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fixup(R, S, MP, MM, K, B, false) ->
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case (R + MP > S) of
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true -> {K + 1, generate(R, S, MP, MM, B, true)}
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; false -> {K, generate(R * B, S, MP * B, MM * B, B, true)}
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end.
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generate(RT, S, MP, MM, B, Round) ->
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D = RT div S,
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R = RT rem S,
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TC1 = case Round of true -> (R =< MM); false -> (R < MM) end,
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TC2 = case Round of true -> (R + MP >= S); false -> (R + MP > S) end,
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case TC1 of
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false -> case TC2 of
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false -> [D | generate(R * B, S, MP * B, MM * B, B, Round)]
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; true -> [D + 1]
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end
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; true -> case TC2 of
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false -> [D]
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; true -> case R * 2 < S of
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true -> [D]
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; false -> [D + 1]
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end
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end
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end.
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%% this is not efficient at all and should be replaced with a lookup table
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%% probably
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pow(_B, 0) -> 1;
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pow(B, E) when E > 0 -> pow(B, E, 1).
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pow(B, E, Acc) when E < 2 -> B * Acc;
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pow(B, E, Acc) when E band 1 == 1 -> pow(B * B, E bsr 1, B * Acc);
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pow(B, E, Acc) -> pow(B * B, E bsr 1, Acc).
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digits_to_list(0, Digits) ->
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digits_to_list(Digits, ignore, ".0");
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digits_to_list(Dpoint, Digits) when Dpoint =< length(Digits), Dpoint > 0 ->
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digits_to_list(Digits, Dpoint, []);
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digits_to_list(Dpoint, Digits) when Dpoint > 0 ->
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Pad = Dpoint - length(Digits),
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case Pad of
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X when X > 6 ->
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digits_to_list(Digits, 1, []) ++ "e" ++ integer_to_list(Dpoint - 1)
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; _ ->
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digits_to_list(Digits ++ [ 0 || _ <- lists:seq(1, Pad)], Dpoint, [])
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end;
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digits_to_list(Dpoint, Digits) when Dpoint < 0 ->
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digits_to_list(Digits, 1, []) ++ "e" ++ integer_to_list(Dpoint - 1).
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digits_to_list([], 0, Acc) ->
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lists:reverse("0." ++ Acc);
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digits_to_list([], ignore, Acc) ->
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lists:reverse(Acc);
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digits_to_list(Digits, 0, Acc) ->
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digits_to_list(Digits, ignore, "." ++ Acc);
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digits_to_list([Digit|Digits], Dpoint, Acc) ->
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digits_to_list(Digits,
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case Dpoint of ignore -> ignore; X -> X - 1 end, [to_hex(Digit)] ++ Acc
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).
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%% json string escaping, for utf8 binaries. escape the json control sequences to
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%% their json equivalent, escape other control characters to \uXXXX sequences,
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%% everything else should be a legal json string component
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@ -253,43 +121,6 @@ to_hex(X) -> X + 48. %% ascii "1" is [49], "2" is [50], etc...
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%% eunit tests
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-ifdef(TEST).
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-include_lib("eunit/include/eunit.hrl").
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nice_decimal_test_() ->
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[
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{"0.0", ?_assert(nice_decimal(0.0) =:= "0.0")},
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{"1.0", ?_assert(nice_decimal(1.0) =:= "1.0")},
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{"-1.0", ?_assert(nice_decimal(-1.0) =:= "-1.0")},
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{"3.1234567890987654321",
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?_assert(
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nice_decimal(3.1234567890987654321) =:= "3.1234567890987655")
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},
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{"1.0e23", ?_assert(nice_decimal(1.0e23) =:= "1.0e23")},
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{"0.3", ?_assert(nice_decimal(3.0/10.0) =:= "0.3")},
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{"0.0001", ?_assert(nice_decimal(0.0001) =:= "1.0e-4")},
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{"0.00000001", ?_assert(nice_decimal(0.00000001) =:= "1.0e-8")},
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{"1.0e-323", ?_assert(nice_decimal(1.0e-323) =:= "1.0e-323")},
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{"1.0e308", ?_assert(nice_decimal(1.0e308) =:= "1.0e308")},
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{"min normalized float",
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?_assert(
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nice_decimal(math:pow(2, -1022)) =:= "2.2250738585072014e-308"
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)
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},
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{"max normalized float",
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?_assert(
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nice_decimal((2 - math:pow(2, -52)) * math:pow(2, 1023))
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=:= "1.7976931348623157e308"
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)
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},
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{"min denormalized float",
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?_assert(nice_decimal(math:pow(2, -1074)) =:= "5.0e-324")
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},
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{"max denormalized float",
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?_assert(
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nice_decimal((1 - math:pow(2, -52)) * math:pow(2, -1022))
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=:= "2.225073858507201e-308"
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)
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}
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].
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binary_escape_test_() ->
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