#pragma OPENCL EXTENSION cl_khr_fp16 : enable

DESCRIPTION
This extension adds support for half scalar and vector types as builtin 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 builtin scalar and vector data types are extended to include the types in the table below.
The builtin 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 builtin 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  2component halfprecision floatingpoint vector 
cl_half2

half3  3component halfprecision floatingpoint vector 
cl_half3

half4  4component halfprecision floatingpoint vector 
cl_half4

half8  8component halfprecision floatingpoint vector 
cl_half8

half16  16component halfprecision floatingpoint vector 
cl_half16

The relational, equality, logical and logical unary operators(3clc) 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  0x1.0p14h 
HALF_MIN

#define HALF_EPSILON  0x1.0p10h 
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 opcode CL_DEVICE_HALF_FP_CONFIG with clGetDeviceInfo(3clc) for an OpenCL device that supports half precision floatingpoint.
SPECIFICATION
m[blue]OpenCL Specificationm[][1]
AUTHORS
The Khronos Group
COPYRIGHT
Copyright © 20072011 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or associated documentation files (the "Materials"), to deal in the Materials without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to the condition that this copyright notice and permission notice shall be included in all copies or substantial portions of the Materials.
NOTES
 1.

OpenCL Specification
 page 14, section 9.5  Half FloatingPoint