Data Types

OpenCL data types.

Description

These are the data types available in the OpenCL C programming language. Click on a category name in the table below to see information about specific data types.

Data type category Included data types
Scalar data types bool, char, cl_char, unsigned char, uchar, cl_uchar, short, cl_short, unsigned short, ushort, int, unsigned int, uint, long, unsigned long, ulong, float, half, size_t, ptrdiff_t, intptr_t, uintptr_t, void, double, and half floating point types.
Vector data types charn, ucharn, shortn, ushortn, intn, uintn, longn, ulongn, floatn, doublen, and optional halfn types.
Abstract data types cl_platform_id, cl_device_id, cl_context, cl_command_queue, cl_mem, cl_program, cl_kernel, cl_event, and cl_sampler.
Reserved Data Types booln, halfn, quad, quadn, complex half, complex halfn, imaginary half, imaginary halfn, complex float, complex floatn, imaginary float, imaginary floatn, complex double, complex doublen, imaginary double, imaginary doublen, complex quad, complex quadn, imaginary quad, imaginary quadn, floatnxm, doublenxm, long double, long doublen, long long, long longn, unsigned long long, ulong long, and ulong longn.
Other data types image2d_t, image3d_t, image2d_array_t, image1d_t, image31_buffer_t, image1d_array_t, sampler_t, and event_t.

Alignment of Types

A data item declared to be a data type in memory is always aligned to the size of the data type in bytes. For example, a float4 variable will be aligned to a 16-byte boundary, and a char2 variable will be aligned to a 2-byte boundary.

For 3-component vector data types, the size of the data type is 4 * sizeof(component). This means that a 3-component vector data type will be aligned to a 4 * sizeof(component) boundary. The vload3 and vstore3 built-in functions can be used to read and write, respectively, 3-component vector data types from an array of packed scalar data type.

A built-in data type that is not a power of two bytes in size must be aligned to the next larger power of two. This rule applies to built-in types only, not structs or unions.

The OpenCL compiler is responsible for aligning data items to the appropriate alignment as required by the data type. For arguments to a __kernel function declared to be a pointer to a data type, the OpenCL compiler can assume that the pointee is always appropriately aligned as required by the data type. The behavior of an unaligned load or store is undefined, except for the vloadn, vload_halfn, vstoren, and vstore_halfn functions. The vector load functions can read a vector from an address aligned to the element type of the vector. The vector store functions can write a vector to an address aligned to the element type of the vector.

The user is responsible for ensuring that data passed into and out of OpenCL buffers are natively aligned relative to the start of the buffer as described above. This implies that OpenCL buffers created with CL_MEM_USE_HOST_PTR need to provide an appropriately aligned host memory pointer that is aligned to the data types used to access these buffers in a kernel(s). As well, the user is responsible to ensure that data passed into and out of OpenCL images are properly aligned to the granularity of the data representing a single pixel (e.g. image_num_channels * sizeof(image_channel_data_type)) except for CL_RGB and CL_RGBx images where the data must be aligned to the granularity of a single channel in a pixel (i.e. sizeof(image_channel_data_type)).

OpenCL makes no requirement about the alignment of OpenCL application defined data types outside of buffers and images, except that the underlying vector primitives (e.g. __cl_float4) where defined shall be directly accessible as such using appropriate named fields in the cl_type union. Nevertheless, it is recommended that the cl_platform.h header should attempt to naturally align OpenCL defined application data types (e.g. cl_float4) according to their type.

Specification

OpenCL Specification

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