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tidy up and expound more on how half-float works. 

llvm-svn: 98524
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Chris Lattner 2010-03-14 23:03:31 +00:00
parent 9fa851b9d4
commit bbd8bd3257
1 changed files with 21 additions and 14 deletions
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llvm/docs/LangRef.html
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@ -257,8 +257,8 @@
</li>
<li><a href="#int_fp16">Half Precision Floating Point Intrinsics</a>
<ol>
<li><a href="#int_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
<li><a href="#int_from_fp16">'<tt>llvm.conver.from.fp16</tt>' Intrinsic</a></li>
<li><a href="#int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a></li>
<li><a href="#int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a></li>
</ol>
</li>
<li><a href="#int_debugger">Debugger intrinsics</a></li>
@ -6619,16 +6619,23 @@ LLVM</a>.</p>
<div class="doc_text">
<p>Half precision floating point is storage-only format. That is why the values
in such format should be promoted to single precision format before any
operations. LLVM provides intrinsics for conversions to single precision and
back.</p>
<p>Half precision floating point is storage-only format. This means that it is
an encoding (typically for density in memory) but typically does not support
computation in the format.</p>
<p>This means that you code must first load the half-precision floating point
value as an i16, then convert it to float with <a
href="#int_convert_from_fp16"><tt>llvm.convert.from.fp16</tt></a>.
Computation can then be performed on the float value (including extending to
double etc). When the value is ready to be stored back to memory, this is
done by converting to float if needed, then converting to i16 with
<a href="#int_convert_to_fp16"><tt>llvm.convert.to.fp16</tt></a>, then
storing as an i16 value.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="int_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a>
<a name="int_convert_to_fp16">'<tt>llvm.convert.to.fp16</tt>' Intrinsic</a>
</div>
<div class="doc_text">
@ -6650,8 +6657,8 @@ LLVM</a>.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.convert.to.fp16</tt>' intrinsic function performs
a conversion from single precision floating point format to half precision
floating point format. Since the format is storage only the return value is
just an <tt>i16</tt> which contains the converted number.</p>
floating point format. The return value is just an <tt>i16</tt> which
contains the converted number.</p>
<h5>Examples:</h5>
<pre>
@ -6663,7 +6670,7 @@ LLVM</a>.</p>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="int_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a>
<a name="int_convert_from_fp16">'<tt>llvm.convert.from.fp16</tt>' Intrinsic</a>
</div>
<div class="doc_text">
@ -6684,9 +6691,9 @@ LLVM</a>.</p>
<h5>Semantics:</h5>
<p>The '<tt>llvm.convert.from.fp16</tt>' intrinsic function performs a
conversion from half single precision floating point format to signle
precision floating point format. Since the format is storage only the
argument is represented by an <tt>i16</tt> value.</p>
conversion from half single precision floating point format to signgle
precision floating point format. The input half-float value is represented by
an <tt>i16</tt> value.</p>
<h5>Examples:</h5>
<pre>