<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
p.msonormal0, li.msonormal0, div.msonormal0
{mso-style-name:msonormal;
margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
p.xmsonormal, li.xmsonormal, div.xmsonormal
{mso-style-name:x_msonormal;
margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.EmailStyle21
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The doc Sam referenced seems to be implying that sizeof(_Float16) is allowed to be 4 if the target doesn’t support “native” half precision operations. Is that correct? That would be a showstopper for OpenCL where sizeof(half) must be
2.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Brian<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Anastasia Stulova <Anastasia.Stulova@arm.com> <br>
<b>Sent:</b> Monday, October 22, 2018 3:42 PM<br>
<b>To:</b> Liu, Yaxun (Sam) <Yaxun.Liu@amd.com>; Bader, Alexey <alexey.bader@intel.com>; Sumner, Brian <Brian.Sumner@amd.com>; cfe-dev (cfe-dev@lists.llvm.org) <cfe-dev@lists.llvm.org><br>
<b>Cc:</b> nd <nd@arm.com><br>
<b>Subject:</b> Re: [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div id="divtagdefaultwrapper">
<p><span style="font-size:12.0pt;color:black">Hi Sam,<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">I would disagree regarding the requirements on the half implementation. Section 6.1.1 explicitly says:<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">"The half data type must conform to the IEEE 754-2008 half precision storage format."<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Do you suggest to change the spec to refer to ISO standard instead of IEEE for half type? I am a bit concerned about backwards compatibility though in case current implementations are relying on the higher precision
arithmetic. Do you know the implications on the precision and ulp bounds?<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Cheers,<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">Anastasia<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<div>
<div class="MsoNormal" align="center" style="text-align:center"><span style="font-size:12.0pt;color:black">
<hr size="3" width="98%" align="center">
</span></div>
<div id="divRplyFwdMsg">
<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> Liu, Yaxun (Sam) <<a href="mailto:Yaxun.Liu@amd.com">Yaxun.Liu@amd.com</a>><br>
<b>Sent:</b> 22 October 2018 15:35<br>
<b>To:</b> Bader, Alexey; Anastasia Stulova; Sumner, Brian; cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>)<br>
<b>Subject:</b> RE: [OpenCL] Representing OpenCL half type by _Float16 type</span><span style="font-size:12.0pt;color:black">
<o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
</div>
</div>
<div>
<div>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Right.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Sam<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="xmsonormal"><b><span style="font-size:12.0pt;color:black">From:</span></b><span style="font-size:12.0pt;color:black"> Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>
<br>
<b>Sent:</b> Monday, October 22, 2018 4:53 AM<br>
<b>To:</b> Liu, Yaxun (Sam) <<a href="mailto:Yaxun.Liu@amd.com">Yaxun.Liu@amd.com</a>>; 'anastasia.stulova@arm.com' <<a href="mailto:anastasia.stulova@arm.com">anastasia.stulova@arm.com</a>>; Sumner, Brian <<a href="mailto:Brian.Sumner@amd.com">Brian.Sumner@amd.com</a>>;
cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> RE: [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></span></p>
</div>
</div>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">The proposal sounds good to me.</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">I assume that by changing OpenCL half data type representation from __fp16 to _Float16, we align it with cl_khr_fp16 extension. There should be no functional changes for programs not using this
extension. Right?</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="xmsonormal"><a name="x______replyseparator"></a><b><span style="font-size:12.0pt;color:black">From:</span></b><span style="font-size:12.0pt;color:black"> Liu, Yaxun (Sam) [<a href="mailto:Yaxun.Liu@amd.com">mailto:Yaxun.Liu@amd.com</a>]
<br>
<b>Sent:</b> Friday, October 19, 2018 6:30 PM<br>
<b>To:</b> Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>; 'anastasia.stulova@arm.com' <<a href="mailto:anastasia.stulova@arm.com">anastasia.stulova@arm.com</a>>; Sumner, Brian <<a href="mailto:Brian.Sumner@amd.com">Brian.Sumner@amd.com</a>>;
cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> RE: [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></span></p>
</div>
</div>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Hi Alexey,<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">We have semantic checks to enforce the restrictions on half type when cl_khr_fp16 is not enabled. We could keep these checks if we switch to _Float16.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Sam<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="xmsonormal"><b><span style="font-size:12.0pt;color:black">From:</span></b><span style="font-size:12.0pt;color:black"> Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>
<br>
<b>Sent:</b> Friday, October 19, 2018 9:16 AM<br>
<b>To:</b> Liu, Yaxun (Sam) <<a href="mailto:Yaxun.Liu@amd.com">Yaxun.Liu@amd.com</a>>; 'anastasia.stulova@arm.com' <<a href="mailto:anastasia.stulova@arm.com">anastasia.stulova@arm.com</a>>; Sumner, Brian <<a href="mailto:Brian.Sumner@amd.com">Brian.Sumner@amd.com</a>>;
cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> RE: [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></span></p>
</div>
</div>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">Hi Sam,</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D"> </span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">I assume OpenCL half type mapped to __fp16 as OpenCL specification defines it as “A 16-bit floating-point conforming to the IEEE 754-2008 half precision storage format”. This aligned with __fp16
description from clang documentation.</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D"> </span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">OpenCL cl_khr_fp16 extension enables arithmetic operations on ‘half’ data types and I think it’s reasonable to map ‘half’ data type to _Float16 if cl_khr_fp16 is enabled.</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D"> </span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">Is it possible to map ‘half’ data type to _Float16 and keep the restrictions of OpenCL core specification?</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D"> </span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">Thanks,</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D">Alexey</span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:#1F497D"> </span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="xmsonormal"><b><span style="font-size:12.0pt;color:black">From:</span></b><span style="font-size:12.0pt;color:black"> Liu, Yaxun (Sam) [<a href="mailto:Yaxun.Liu@amd.com">mailto:Yaxun.Liu@amd.com</a>]
<br>
<b>Sent:</b> Wednesday, October 17, 2018 7:31 PM<br>
<b>To:</b> 'anastasia.stulova@arm.com' <<a href="mailto:anastasia.stulova@arm.com">anastasia.stulova@arm.com</a>>; Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>>; Sumner, Brian <<a href="mailto:Brian.Sumner@amd.com">Brian.Sumner@amd.com</a>>;
cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> [OpenCL] Representing OpenCL half type by _Float16 type<o:p></o:p></span></p>
</div>
</div>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Hi,<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Clang supports two 16 bit floating point builtin types: __fp16 and _Float16. Their differences are here<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"><a href="https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point">https://clang.llvm.org/docs/LanguageExtensions.html#half-precision-floating-point</a><o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Currently clang supports OpenCL half type as __fp16, one significant disadvantage of which is that arithmetic operations are emitted as fp32 instead of fp16 instructions in LLVM IR. Another disadvantage
is interoperability with C++ programs, which uses _Float16 mostly since it is an ISO standard whereas __fp16 is not.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">OpenCL spec v 2.0 s 6.1.1.1 (<a href="https://www.khronos.org/registry/OpenCL/specs/opencl-2.0-openclc.pdf">https://www.khronos.org/registry/OpenCL/specs/opencl-2.0-openclc.pdf</a> ) defines half
type. There is no requirement that it has to be __fp16 or _Float16 type in clang. Actually, it seems both __fp16 and _Float16 can be used to represent OpenCL half type.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Considering the advantages of _Float16 type, I am wondering whether we should consider using _Float16 to represent OpenCL half type.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Any comments are welcome.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Thanks.<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">Yaxun (Sam) Liu<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black">AMD<o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p class="xmsonormal"><span style="font-size:12.0pt;color:black"> <o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><br>
--------------------------------------------------------------------<br>
Joint Stock Company Intel A/O<br>
Registered legal address: Krylatsky Hills Business Park, <br>
17 Krylatskaya Str., Bldg 4, Moscow 121614, <br>
Russian Federation<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">This e-mail and any attachments may contain confidential material for<br>
the sole use of the intended recipient(s). Any review or distribution<br>
by others is strictly prohibited. If you are not the intended<br>
recipient, please contact the sender and delete all copies.<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black"><br>
--------------------------------------------------------------------<br>
Joint Stock Company Intel A/O<br>
Registered legal address: Krylatsky Hills Business Park, <br>
17 Krylatskaya Str., Bldg 4, Moscow 121614, <br>
Russian Federation<o:p></o:p></span></p>
<p><span style="font-size:12.0pt;color:black">This e-mail and any attachments may contain confidential material for<br>
the sole use of the intended recipient(s). Any review or distribution<br>
by others is strictly prohibited. If you are not the intended<br>
recipient, please contact the sender and delete all copies.<o:p></o:p></span></p>
</div>
</div>
</div>
</div>
</div>
</body>
</html>