cl_khr_fp16.adoc

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cl_khr_fp16

Optional half floating-point support.

#pragma OPENCL EXTENSION cl_khr_fp16 : enable

Description

This extension adds support for half scalar and vector types as built-in types that can be used for arithmetic operations, conversions, etc. An application that wants to use half and halfn types will need to include the directive shown above.

The list of built-in scalar and vector data types are extended to include the types in the table below.

The built-in vector data types for halfn are also declared as appropriate types in the OpenCL API (and header files) that can be used by an application. The following table describes the built-in vector data types for halfn as defined in the OpenCL C programming language and the corresponding data type available to the application:

Type in OpenCL Language	Description	API type for application
half2	2-component half-precision floating-point vector	cl_half2
half3	3-component half-precision floating-point vector	cl_half3
half4	4-component half-precision floating-point vector	cl_half4
half8	8-component half-precision floating-point vector	cl_half8
half16	16-component half-precision floating-point vector	cl_half16

The relational, equality, logical and logical unary operators can be used with half scalar and halfn vector types and shall produce a scalar int and vector shortn result respectively.

The OpenCL compiler accepts an h and H suffix on floating point literals, indicating the literal is typed as a half.

The macro names given in the following list must use the values specified. These constant expressions are suitable for use in #if preprocessing directives.

The following table also describes the corresponding macro names available to the application.

Macro in OpenCL Language	value	Macro for application
#define HALF_DIG	3	HALF_DIG
#define HALF_MANT_DIG	11	HALF_MANT_DIG
#define HALF_MAX_10_EXP	+4	HALF_MAX_10_EXP
#define HALF_MAX_EXP	+16	HALF_MAX_EXP
#define HALF_MIN_10_EXP	-4	HALF_MIN_10_EXP
#define HALF_MIN_EXP	-13	HALF_MIN_EXP
#define HALF_RADIX	2	HALF_RADIX
#define HALF_MAX	0x1.ffcp15h	HALF_MAX
#define HALF_MIN	0x1.0p-14h	HALF_MIN
#define HALF_EPSILON	0x1.0p-10h	HALF_EPSILON

The following constants are also available. They are of type half and are accurate within the precision of the half type.

Constant	Description
M_E_H	Value of e
M_LOG2E_H	Value of log2 e
M_LOG10E_H	Value of log10 e
M_LN2_H	Value of ln 2
M_LN10_H	Value of ln 10
M_PI_H	Value of π
M_PI_2_H	Value of π / 2
M_PI_4_H	Value of π / 4
M_1_PI_H	Value of 1 / π
M_2_PI_H	Value of 2 / π
M_2_SQRTPI_H	Value of 2 / √π
M_SQRT2_H	Value of √2
M_SQRT1_2_H	Value of 1 / √2

Ann application may query the configuration information using the op-code CL_DEVICE_HALF_FP_CONFIG with clGetDeviceInfo for an OpenCL device that supports half precision floating-point.

Conversions

The implicit conversion rules specified in section 6.2.1 now include the half scalar and halfn vector data types.

The explicit casts described in section 6.2.2 are extended to take a half scalar data type and a halfn vector data type.

The explicit conversion functions described in section 6.2.3 are extended to take a half scalar data type and a halfn vector data type.

The as_typen() function for re-interpreting types as described in section 6.2.4.2 is extended to allow conversion-free casts between shortn, ushortn and halfn scalar and vector data types.

Also see

EXTENSION, clGetDeviceInfo, mathFunctions, commonFunctions, geometricFunctions, relationalFunctions, vectorDataLoadandStoreFunctions, asyncCopyFunctions, imageFunctions

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