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| <title>SELECT_ROUNDING_MODE</title> |
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| <div xmlns="" class="refnamediv"> |
| <a xmlns="http://www.w3.org/1999/xhtml" id="SELECT_ROUNDING_MODE"></a> |
| <h1>SELECT_ROUNDING_MODE</h1> |
| <p> |
| Specify the rounding mode for an instruction or group of instructions. |
| </p> |
| </div> |
| <div class="refsect2"> |
| <a id="synopsis"></a> |
| <h3> |
| </h3> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
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| <tbody> |
| <tr> |
| <td align="left"> |
| #pragma OPENCL SELECT_ROUNDING_MODE <code class="varname">rounding-mode</code> |
| </td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="parameters"></a> |
| <h2>Parameters</h2> |
| <div class="variablelist"> |
| <dl class="variablelist"> |
| <dt> |
| <span class="term"> |
| <code class="varname"> |
| rounding-mode |
| </code> |
| </span> |
| </dt> |
| <dd> |
| <p> |
| One of the following values: |
| </p> |
| <div class="informaltable"> |
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| <colgroup> |
| <col align="left" class="col1" /> |
| <col align="left" class="col2" /> |
| </colgroup> |
| <thead> |
| <tr> |
| <th align="left"> |
| <span class="emphasis"> |
| <em>rounding-mode</em> |
| </span> |
| </th> |
| <th align="left">Description</th> |
| </tr> |
| </thead> |
| <tbody> |
| <tr> |
| <td align="left">rte</td> |
| <td align="left">round to nearest even</td> |
| </tr> |
| <tr> |
| <td align="left">rtz</td> |
| <td align="left">round to zero</td> |
| </tr> |
| <tr> |
| <td align="left">rtp</td> |
| <td align="left">round to positive infinity</td> |
| </tr> |
| <tr> |
| <td align="left">rtn</td> |
| <td align="left">round to negative infinity</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </dd> |
| </dl> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="description"></a> |
| <h2>Description</h2> |
| <p> |
| OpenCL 1.0 adds support for specifying the rounding mode for an instruction or group of instructions in the program source as an optional extension. An application that wants to use this feature will need to include the <code class="function">#pragma OPENCL EXTENSION |
| <a class="citerefentry" href="cl_khr_select_fprounding_mode.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_select_fprounding_mode</span></span></a> : enable</code> directive. </p> |
| <p>If the <a class="citerefentry" href="cl_khr_select_fprounding_mode.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_select_fprounding_mode</span></span></a> extension is supported, the OpenCL implementation must support all four rounding modes for single precision floating-point i.e. the <code class="constant">CL_DEVICE_SINGLE_FP_CONFIG</code> described in the table of OpenCL Device Queries for <a class="citerefentry" href="clGetDeviceInfo.html"><span class="citerefentry"><span class="refentrytitle">clGetDeviceInfo</span></span></a>. must include |
| <code class="constant">CL_FP_ROUND_TO_ZERO</code> and <code class="constant">CL_FP_ROUND_TO_INF</code>. This is already the case for double |
| precision floating-point. </p> |
| <p>The appropriate rounding mode can be specified using <code class="function">#pragma OPENCL SELECT_ROUNDING_MODE <code class="varname">rounding-mode</code></code> in the program source. |
| </p> |
| <p> |
| The <code class="function">#pragma OPENCL SELECT_ROUNDING_MODE</code> sets the rounding mode for all |
| instructions that operate on floating-point types (scalar or vector types) or produce floating-point |
| values that follow this pragma in the program source until the next <code class="function">#pragma OPENCL SELECT_ROUNDING_MODE</code> is encountered. Note that the rounding mode specified for a block of code is known at compile time. Except where otherwise documented, the callee functions do not inherit the rounding mode of the caller function. |
| </p> |
| <p> |
| If this extension is enabled, the <code class="function">__ROUNDING_MODE__</code> preprocessor symbol shall be defined to be one of the following according to the current rounding mode: |
| </p> |
| <p> |
| <code class="constant"> |
| <div class="literallayout"> |
| <p><br /> |
| #define __ROUNDING_MODE__ rte<br /> |
| #define __ROUNDING_MODE__ rtz<br /> |
| #define __ROUNDING_MODE__ rtp<br /> |
| #define __ROUNDING_MODE__ rtz<br /> |
| <br /> |
| This is intended to let us remap foo() to foo_rte() in the preprocessor using<br /> |
| #define foo foo ## __ROUNDING_MODE__<br /> |
| </p> |
| </div> |
| </code> |
| </p> |
| <p> |
| The default rounding mode is round to nearest even. The built-in <a class="citerefentry" href="mathFunctions.html"><span class="citerefentry"><span class="refentrytitle">math functions</span></span></a>, the <a class="citerefentry" href="commonFunctions.html"><span class="citerefentry"><span class="refentrytitle">common functions</span></span></a>, and the <a class="citerefentry" href="geometricFunctions.html"><span class="citerefentry"><span class="refentrytitle">geometric functions</span></span></a> are implemented with the round to nearest even rounding mode. </p> |
| <p> |
| Various built-in conversions and the <a class="citerefentry" href="vstore_half.html"><span class="citerefentry"><span class="refentrytitle">vstore_half</span></span></a> and |
| <a class="citerefentry" href="vstorea_halfn.html"><span class="citerefentry"><span class="refentrytitle">vstorea_half<span class="emphasis"><em>n</em></span></span></span></a> built-in functions that do not specify a rounding mode inherit the current rounding mode. Conversions from floating-point to integer type always use <code class="constant">rtz</code> mode, except where the user specifically asks for another rounding mode. |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="notes"></a> |
| <h2>Notes</h2> |
| <p> |
| The above four rounding modes are defined by IEEE 754. Floating-point calculations may be carried out internally with extra precision and then rounded to fit into the destination type. <span class="emphasis"><em>Round to nearest even</em></span> is currently the only rounding mode required by the OpenCL specification and is therefore the default rounding mode. In addition, only static selection of rounding mode is supported. Dynamically reconfiguring the rounding modes as specified by the IEEE 754 spec is not a requirement. |
| </p> |
| </div> |
| <div class="refsect2"> |
| <a id="example1"></a> |
| <h3> |
| Example |
| </h3> |
| <div class="informaltable"> |
| <table class="informaltable" border="0"> |
| <colgroup> |
| <col align="left" class="col1" /> |
| </colgroup> |
| <tbody> |
| <tr> |
| <td align="left">#pragma OPENCL SELECT_ROUNDING_MODE rtz |
| float4 a = b * c; // uses round to zero rounding mode. |
| |
| #pragma OPENCL SELECT_ROUNDING_MODE rtp |
| float4 d = foo(a); // function foo uses rounding mode |
| specified where source for foo() is |
| implemented.</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
| </div> |
| <div class="refsect1"> |
| <a id="specification"></a> |
| <h2>Specification</h2> |
| <p> |
| <img src="pdficon_small1.gif" /> |
| |
| <a href="http://www.khronos.org/registry/cl/specs/opencl-1.0.pdf#page=242" target="OpenCL Spec">OpenCL Specification</a> |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a id="seealso"></a> |
| <h2>Also see</h2> |
| <p> |
| <a class="citerefentry" href="cl_khr_select_fprounding_mode.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_select_fprounding_mode</span></span></a> |
| </p> |
| </div> |
| <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2009 The Khronos Group Inc. |
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