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<p>A library that implements IEEE-754: <a class="moz-txt-link-freetext" href="http://speleotrove.com/decimal/">http://speleotrove.com/decimal/</a>
</p>
<p>Example implementations in Erlang:<br>
</p>
<p><a class="moz-txt-link-freetext" href="https://github.com/tim/erlang-decimal">https://github.com/tim/erlang-decimal</a><br>
</p>
<p><a class="moz-txt-link-freetext" href="https://github.com/egobrain/decimal">https://github.com/egobrain/decimal</a></p>
<p><br>
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<div class="moz-cite-prefix">On 3/17/19 1:29 AM, Richard O'Keefe
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CABcYAdJzRFC5i7exXXtV-BwV7hUL2S3j06FnKao8=EruS4jAhg@mail.gmail.com">
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<div class="gmail_default"
style="font-family:monospace,monospace">What do you mean by "a
decimal lib"?<br>
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<br>
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<div dir="ltr" class="gmail_attr">On Sun, 17 Mar 2019 at 06:35,
Bryan Paxton <<a href="mailto:starbelly@pobox.com"
moz-do-not-send="true">starbelly@pobox.com</a>> wrote:<br>
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<p> All of this begs the question of why there is no decimal
lib in otp... I'm sure there's a good reason... ?</p>
<p><br>
</p>
<div class="gmail-m_555742592463524003moz-cite-prefix">On
3/16/19 12:31 PM, Bob Ippolito wrote:<br>
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<blockquote type="cite">
<div dir="ltr">While it's more code, the most
straightforward way would be to parse the whole float
for that spec into its constituent parts and reassemble
(with defaults where necessary) to parse with
float_to_list.
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<div dir="ltr" class="gmail_attr">On Sat, Mar 16, 2019
at 4:32 AM Hugo Mills <<a
href="mailto:hugo@carfax.org.uk" target="_blank"
moz-do-not-send="true">hugo@carfax.org.uk</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px
0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"> Hi, Bob,<br>
<br>
On Fri, Mar 15, 2019 at 05:32:54PM -0700, Bob Ippolito
wrote:<br>
> If you dive into the implementation it's
effectively a wrapper around<br>
> strtod from C with a validation pass that is more
strict than the strtod<br>
> standard.<br>
> <br>
> <a
href="https://github.com/erlang/otp/blob/OTP-21.3/erts/emulator/sys/win32/sys_float.c#L54"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://github.com/erlang/otp/blob/OTP-21.3/erts/emulator/sys/win32/sys_float.c#L54</a><br>
> <a
href="https://github.com/erlang/otp/blob/OTP-21.3/erts/emulator/sys/unix/sys_float.c#L732"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://github.com/erlang/otp/blob/OTP-21.3/erts/emulator/sys/unix/sys_float.c#L732</a><br>
> <br>
> So as far as a regex goes it would be something
like this:<br>
> <br>
> [+-]?\d+[.,]\d+([eE][+-]?\d+)<br>
> <br>
> The major differences between this and other
popular float grammars are:<br>
> <br>
> * At least one digit is required in each part<br>
> * Both integer and fractional parts are required,
even if there's an<br>
> exponent part (so "1", ".1", "1e-1" would not be
valid)<br>
> * The decimal separator is either , or . (the
implementation will try the<br>
> other if necessary to compensate for a different
locale)<br>
<br>
Thanks for the confirmation. That's more or less
what I discovered<br>
while playing around with list_to_float. It's the
first two cases that<br>
are the problems for me, because the spec I'm working
to(*) says that<br>
"1." and ".3" are valid floats, for example, as is
"1e-1".<br>
<br>
Just for the record, here's the code I'm using to
convert a Turtle<br>
double or decimal (the former in scientific notation;
the latter<br>
without the E) into a form suitable for
list_to_float/1:<br>
<br>
[...]<br>
% W3C's description of a float is wider than
erlang's. We need to<br>
% split up the number into a few parts to add
extra characters<br>
% where necessary so that list_to_float/1 will
work right.<br>
F = case string:lexemes(Text, "eE") of<br>
[M, E] -><br>
fixup_decimal(M) ++ "e" ++ E;<br>
[M] -><br>
fixup_decimal(M)<br>
end,<br>
O = lagra_model:new_literal(list_to_float(F)),<br>
[...]<br>
<br>
-spec fixup_decimal(string()) -> string().<br>
fixup_decimal(M) -><br>
case string:lexemes(M, ".") of<br>
[I] -><br>
I++".0";<br>
[I, ""] -><br>
I++".0";<br>
["", J] -><br>
"0."++J;<br>
[I, J] -><br>
M<br>
end.<br>
<br>
Hugo.<br>
<br>
(*) W3C's Turtle recommendation.<br>
<br>
<br>
> On Fri, Mar 15, 2019 at 3:52 PM Hugo Mills <<a
href="mailto:hugo@carfax.org.uk" target="_blank"
moz-do-not-send="true">hugo@carfax.org.uk</a>>
wrote:<br>
> <br>
> > Where in the manual is the set of
allowable string representations<br>
> > of floating point numbers documented? I'd
have expected it to be here:<br>
> ><br>
> > <a
href="http://erlang.org/doc/reference_manual/data_types.html"
rel="noreferrer" target="_blank"
moz-do-not-send="true">http://erlang.org/doc/reference_manual/data_types.html</a><br>
> ><br>
> > ... but apparently not.<br>
> ><br>
> > Specifically, I'm trying to use
list_to_float/1, and I've been<br>
> > trying to reverse engineer it:<br>
> ><br>
> > 1> list_to_float("-1").<br>
> > ** exception error: bad argument<br>
> > in function list_to_float/1<br>
> > called as list_to_float("-1")<br>
> > 2> list_to_float("-1.0").<br>
> > -1.0<br>
> > 3> list_to_float("-1.0e-23").<br>
> > -1.0e-23<br>
> > 4> list_to_float("-1e-23").<br>
> > ** exception error: bad argument<br>
> > in function list_to_float/1<br>
> > called as list_to_float("-1e-23")<br>
> > 5> list_to_float(".3").<br>
> > ** exception error: bad argument<br>
> > in function list_to_float/1<br>
> > called as list_to_float(".3")<br>
> ><br>
> > An actual written specification would be
really handy here. Even<br>
> > just a regex or EBNF for them. I'm writing a
parser for something<br>
> > where the definition of floating point
literals isn't quite the same<br>
> > as Erlang's, and it's a bit painful.<br>
> ><br>
> > Hugo.<br>
> ><br>
<br>
-- <br>
Hugo Mills | Nostalgia isn't what it used
to be.<br>
hugo@... <a href="http://carfax.org.uk"
rel="noreferrer" target="_blank"
moz-do-not-send="true">carfax.org.uk</a> |<br>
<a href="http://carfax.org.uk/" rel="noreferrer"
target="_blank" moz-do-not-send="true">http://carfax.org.uk/</a>
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<p><br>
</p>
<p>--</p>
<p>Bryan Paxton<br>
</p>
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