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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

> 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>