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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-5E358AB4-03A7-5859-ABF2-A8B64B74AF56" xml:lang="en"><title>Vector
Floating Point Architecture (VFP)</title><shortdesc>Describes the implementation of the ARM Vector Floating Point Architecture
(VFPv2) on Symbian platform. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>ARM provide a hardware floating point coprocessor that provides floating
point computation that is fully compliant with IEEE Std 754-1985.We refer
to the coprocessor as the <i>VFP unit</i>. </p>
<p>Symbian platform supports the use of VFPv2 on platforms where the required
hardware is present in both <i>RunFast</i> mode and in <i>IEEE-without-exceptions</i> mode.
See ARM's Vector Floating-point Coprocessor Technical reference Manual for
more details on the coprocessor, its architecture, and its execution modes. </p>
<p>You should read the information in <xref href="GUID-D525B9A9-6B32-535B-A282-60C85A48D3FB.dita">Floating
point support</xref> about applications and user side code as this is also
applicable to code running on the kernel side. However there are a number
of restrictions that must be observed: </p>
<ul>
<li id="GUID-2205026D-0E6F-54AE-B74F-5478D6047B70"><p>You <i>cannot</i> use
VFP instructions in any interrupt service routine. </p> </li>
<li id="GUID-C8D896E1-CF36-52CD-A984-61D7A8189268"><p>You <i>cannot</i> use
VFP instructions when the kernel is locked, for example, in an IDFC or after
calling <xref href="GUID-3A3C08F3-3D33-3D9E-80E7-7855C7B21E02.dita#GUID-3A3C08F3-3D33-3D9E-80E7-7855C7B21E02/GUID-7CBBF72B-4519-38DD-92CA-38AF636AFD8A"><apiname>NKern::Lock()</apiname></xref>  </p> </li>
<li id="GUID-A7466A83-A8F2-58CE-AB8B-E05607BB6D95"><p>You <i>cannot</i> use
VFP instructions in any section of code which runs with a fast mutex held. </p> </li>
</ul>
<p>Using VFP instructions in these situations can lead to data being corrupted,
or the kernel panicking. If you rely on the compiler to generate VFP instructions,
rather than using inline assembler, it is extremely important that you do
not use any floating point values in these situations. The compiler may generate
VFP instructions for the most trivial floating point operations and even for
simple assignments. </p>
</conbody></concept>