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authorSverker Eriksson <[email protected]>2018-03-16 19:34:42 +0100
committerSverker Eriksson <[email protected]>2018-04-04 14:31:14 +0200
commit9091e0fc630913999e3a51e860a2c4e07c6143c1 (patch)
tree554aefe8ae6ee1d37ba106f91a03eacc15e1f2a7 /erts/emulator/test/num_bif_SUITE.erl
parentd171399bb5a0e9f4c6029564ece4fbf89f3c76f8 (diff)
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erts: Fix float_to_list(F, [{decimals,D}])
to better conform with io_lib:format("~.*f", [D,F])
Diffstat (limited to 'erts/emulator/test/num_bif_SUITE.erl')
-rw-r--r--erts/emulator/test/num_bif_SUITE.erl25
1 files changed, 25 insertions, 0 deletions
diff --git a/erts/emulator/test/num_bif_SUITE.erl b/erts/emulator/test/num_bif_SUITE.erl
index 592542405f..104bd37817 100644
--- a/erts/emulator/test/num_bif_SUITE.erl
+++ b/erts/emulator/test/num_bif_SUITE.erl
@@ -213,6 +213,20 @@ fts_rand_float_decimals(N) ->
[begin
F0 = rand_float_reasonable(),
L0 = float_to_list(F0, [{decimals, D}]),
+ case conform_with_io_lib_format(F0,D) of
+ false -> ok;
+ true ->
+ IOL = lists:flatten(io_lib:format("~.*f", [D, F0])),
+ true = case L0 =:= IOL of
+ true -> true;
+ false ->
+ io:format("F0 = ~w ~w\n", [F0, <<F0/float>>]),
+ io:format("decimals = ~w\n", [D]),
+ io:format("float_to_list = ~s\n", [L0]),
+ io:format("io_lib:format = ~s\n", [IOL]),
+ false
+ end
+ end,
L1 = case D of
0 -> L0 ++ ".0";
_ -> L0
@@ -234,6 +248,17 @@ fts_rand_float_decimals(N) ->
fts_rand_float_decimals(N-1).
+conform_with_io_lib_format(_, 0) ->
+ %% io_lib:format("~.*f") does not support zero decimals
+ false;
+conform_with_io_lib_format(_, D) when D > 10 ->
+ %% Seems float_to_list gets it slightly wrong sometimes for many decimals
+ false;
+conform_with_io_lib_format(F, D) ->
+ %% io_lib:format prints '0' for input bits beyond mantissa precision
+ %% float_to_list treats those unknown input bits as if they were zeros.
+ math:log2(abs(F) * math:pow(10,D)) < 54.
+
max_diff_decimals(F, D) ->
IntBits = floor(math:log2(abs(F))) + 1,
FracBits = (52 - IntBits),