<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">I'd be hesitant to do that in decimal; it's probably better to add `0x1.0p63` instead. But I guess the approaches are similar: shave off one bit, and then test that bit and adjust the result accordingly.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Nov 11, 2022 at 9:59 AM Remi Forax <<a href="mailto:forax@univ-mlv.fr">forax@univ-mlv.fr</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"><div><div style="font-family:arial,helvetica,sans-serif;font-size:12pt;color:rgb(0,0,0)"><div>Hi all,<br></div><div>I don't know if it's the correct way to do it or if there is a better way, but i'm using<br></div><div><br></div><div> var result = (double) (value & <span>0x7fffffffffffffffL</span>);<br> if (value < 0) {<br> result = result + 9.223372036854776E18;<br> }<br> <br></div><div><br></div><div>The idea is to mask the sign bit, do the conversion to double and if the sign bit was present (if value < 0) add Long.MAX_VALUE + 1 (9223372036854775808) as a double.</div><div><br></div><div>I've got 9.223372036854776E18 as the result of<br></div><div> BigInteger.valueOf(Long.MAX_VALUE).add(BigInteger.ONE).doubleValue()</div><div><br></div><div>Rémi<br></div><div><br></div><hr id="m_3466666749521475928zwchr"><div><blockquote style="border-left:2px solid rgb(16,16,255);margin-left:5px;padding-left:5px;color:rgb(0,0,0);font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt"><b>From: </b>"David Lloyd" <<a href="mailto:david.lloyd@redhat.com" target="_blank">david.lloyd@redhat.com</a>><br><b>To: </b>"Johannes Kuhn" <<a href="mailto:info@j-kuhn.de" target="_blank">info@j-kuhn.de</a>><br><b>Cc: </b>"core-libs-dev" <<a href="mailto:core-libs-dev@openjdk.java.net" target="_blank">core-libs-dev@openjdk.java.net</a>><br><b>Sent: </b>Friday, November 11, 2022 3:38:31 PM<br><b>Subject: </b>Re: Unsigned long to double and back<br></blockquote></div><div><blockquote style="border-left:2px solid rgb(16,16,255);margin-left:5px;padding-left:5px;color:rgb(0,0,0);font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Well, I typed this out from memory so there's an error, of course. `(tmp & 1)` should be `(input & 1)`.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Nov 11, 2022 at 8:31 AM David Lloyd <<a href="mailto:david.lloyd@redhat.com" target="_blank">david.lloyd@redhat.com</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"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">I encountered this issue as well; for now I'm using the following transformation:</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">long tmp = input >>> 1;</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">double output = ((double) tmp) * 2.0 + (tmp & 1);</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">I... *think* it's correct but I'm not 100% sure and have a long-standing TODO to try and figure it out...</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Nov 5, 2022 at 7:17 PM Johannes Kuhn <<a href="mailto:info@j-kuhn.de" target="_blank">info@j-kuhn.de</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">When I tried to implement an WASM transpiler, I noticed some missing <br>
conversion methods from unsigned types to floating point, for example <br>
from unsigned long to a double.<br>
<br>
For the meaning of unsigned long, see Long.toUnsignedString(long i).<br>
<br>
Converting between unsigned long and floating point is not a trivial <br>
task, as it probably requires some bit manipulation.<br>
<br>
In particular, I would love to see the following methods added*:<br>
<br>
- double Double.fromUnsignedLong(long i)<br>
- long Double.toUnsignedLong(double d)<br>
- float Float.fromUnsignedLong(long i)<br>
- long Float.toUnsignedLong(float f)<br>
<br>
* Subject to bikeshedding - I don't care about the name, or if it is <br>
added to the Long class.<br>
<br>
Currently, I don't think that additional methods for unsigned int are <br>
necessary - as it is possible to cast between long and int, but feel <br>
free to correct me.<br>
<br>
In WASM, the specification for those methods can be found here:<br>
<br>
<a href="https://www.w3.org/TR/wasm-core-1/#op-trunc-u" rel="noreferrer" target="_blank">https://www.w3.org/TR/wasm-core-1/#op-trunc-u</a><br>
<a href="https://www.w3.org/TR/wasm-core-1/#op-convert-u" rel="noreferrer" target="_blank">https://www.w3.org/TR/wasm-core-1/#op-convert-u</a><br>
<br>
Note that the WASM specification is undefined for some values, notably <br>
NaN, infinities, and values that fall out of the range.<br>
<br>
As *I* want to use it to implement WASM instructions, I do not have any <br>
strong opinion on the undefined cases - for example, returning the <br>
nearest unsigned long value or throwing an exception is fine for me.<br>
<br>
What do you think?<br>
<br>
- Johannes<br>
<br>
</blockquote></div><br clear="all"><br>-- <br><div dir="ltr"><div dir="ltr">- DML • he/him<br></div></div>
</blockquote></div><br clear="all"><br>-- <br><div dir="ltr"><div dir="ltr">- DML • he/him</div></div><br></blockquote></div></div></div></blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr">- DML • he/him<br></div></div>