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 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 for an
OpenCL device that supports half precision floatingpoint.
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 reinterpreting types as described in section
6.2.4.2 is extended to allow conversionfree casts between
shortn
,
ushortn
and
halfn
scalar and vector data types.
EXTENSION, clGetDeviceInfo, mathFunctions, commonFunctions, geometricFunctions, relationalFunctions, vectorDataLoadandStoreFunctions, asyncCopyFunctions, imageFunctions