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 <a name="Half_002dPrecision"></a>
 <div class="header">
 <p>
 Next: <a href="Decimal-Float.html#Decimal-Float" accesskey="n" rel="next">Decimal Float</a>, Previous: <a href="Floating-Types.html#Floating-Types" accesskey="p" rel="prev">Floating Types</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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 <hr>
 <a name="Half_002dPrecision-Floating-Point"></a>
 <h3 class="section">6.12 Half-Precision Floating Point</h3>
 <a name="index-half_002dprecision-floating-point"></a>
 <a name="index-_005f_005ffp16-data-type"></a>

 <p>On ARM targets, GCC supports half-precision (16-bit) floating point via
 the <code>__fp16</code> type.  You must enable this type explicitly
 with the <samp>-mfp16-format</samp> command-line option in order to use it.
 </p>
 <p>ARM supports two incompatible representations for half-precision
 floating-point values.  You must choose one of the representations and
 use it consistently in your program.
 </p>
 <p>Specifying <samp>-mfp16-format=ieee</samp> selects the IEEE 754-2008 format.
 This format can represent normalized values in the range of <em>2^{-14}</em> to 65504.
 There are 11 bits of significand precision, approximately 3
 decimal digits.
 </p>
 <p>Specifying <samp>-mfp16-format=alternative</samp> selects the ARM
 alternative format.  This representation is similar to the IEEE
 format, but does not support infinities or NaNs.  Instead, the range
 of exponents is extended, so that this format can represent normalized
 values in the range of <em>2^{-14}</em> to 131008.
 </p>
 <p>The <code>__fp16</code> type is a storage format only.  For purposes
 of arithmetic and other operations, <code>__fp16</code> values in C or C++
 expressions are automatically promoted to <code>float</code>.  In addition,
 you cannot declare a function with a return value or parameters
 of type <code>__fp16</code>.
 </p>
 <p>Note that conversions from <code>double</code> to <code>__fp16</code>
 involve an intermediate conversion to <code>float</code>.  Because
 of rounding, this can sometimes produce a different result than a
 direct conversion.
 </p>
 <p>ARM provides hardware support for conversions between
 <code>__fp16</code> and <code>float</code> values
 as an extension to VFP and NEON (Advanced SIMD).  GCC generates
 code using these hardware instructions if you compile with
 options to select an FPU that provides them;
 for example, <samp>-mfpu=neon-fp16 -mfloat-abi=softfp</samp>,
 in addition to the <samp>-mfp16-format</samp> option to select
 a half-precision format.
 </p>
 <p>Language-level support for the <code>__fp16</code> data type is
 independent of whether GCC generates code using hardware floating-point
 instructions.  In cases where hardware support is not specified, GCC
 implements conversions between <code>__fp16</code> and <code>float</code> values
 as library calls.
 </p>
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	<a name="Half_002dPrecision"></a>
	<div class="header">
	<p>
	Next: <a href="Decimal-Float.html#Decimal-Float" accesskey="n" rel="next">Decimal Float</a>, Previous: <a href="Floating-Types.html#Floating-Types" accesskey="p" rel="prev">Floating Types</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Half_002dPrecision-Floating-Point"></a>
	<h3 class="section">6.12 Half-Precision Floating Point</h3>
	<a name="index-half_002dprecision-floating-point"></a>
	<a name="index-_005f_005ffp16-data-type"></a>

	<p>On ARM targets, GCC supports half-precision (16-bit) floating point via
	the <code>__fp16</code> type. You must enable this type explicitly
	with the <samp>-mfp16-format</samp> command-line option in order to use it.
	</p>
	<p>ARM supports two incompatible representations for half-precision
	floating-point values. You must choose one of the representations and
	use it consistently in your program.
	</p>
	<p>Specifying <samp>-mfp16-format=ieee</samp> selects the IEEE 754-2008 format.
	This format can represent normalized values in the range of <em>2^{-14}</em> to 65504.
	There are 11 bits of significand precision, approximately 3
	decimal digits.
	</p>
	<p>Specifying <samp>-mfp16-format=alternative</samp> selects the ARM
	alternative format. This representation is similar to the IEEE
	format, but does not support infinities or NaNs. Instead, the range
	of exponents is extended, so that this format can represent normalized
	values in the range of <em>2^{-14}</em> to 131008.
	</p>
	<p>The <code>__fp16</code> type is a storage format only. For purposes
	of arithmetic and other operations, <code>__fp16</code> values in C or C++
	expressions are automatically promoted to <code>float</code>. In addition,
	you cannot declare a function with a return value or parameters
	of type <code>__fp16</code>.
	</p>
	<p>Note that conversions from <code>double</code> to <code>__fp16</code>
	involve an intermediate conversion to <code>float</code>. Because
	of rounding, this can sometimes produce a different result than a
	direct conversion.
	</p>
	<p>ARM provides hardware support for conversions between
	<code>__fp16</code> and <code>float</code> values
	as an extension to VFP and NEON (Advanced SIMD). GCC generates
	code using these hardware instructions if you compile with
	options to select an FPU that provides them;
	for example, <samp>-mfpu=neon-fp16 -mfloat-abi=softfp</samp>,
	in addition to the <samp>-mfp16-format</samp> option to select
	a half-precision format.
	</p>
	<p>Language-level support for the <code>__fp16</code> data type is
	independent of whether GCC generates code using hardware floating-point
	instructions. In cases where hardware support is not specified, GCC
	implements conversions between <code>__fp16</code> and <code>float</code> values
	as library calls.
	</p>
	<hr>
	<div class="header">
	<p>
	Next: <a href="Decimal-Float.html#Decimal-Float" accesskey="n" rel="next">Decimal Float</a>, Previous: <a href="Floating-Types.html#Floating-Types" accesskey="p" rel="prev">Floating Types</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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