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<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 Floating point support in Symbian^3 Tools Guide
&gt; Building. The guide contains information about applications
and user-side code, which 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>