OpenCL C编程语言规格v3.0.5：统一规范与核心特性

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OpenCL是一种由Khronos Group开发的并行计算平台，专为加速高性能计算任务而设计，特别是针对图形处理单元（GPU）和多核处理器。《OpenCL C编程语言规范》（OpenCL™ C Specification）版本3.0.5，发布于2020年9月30日，涵盖了核心特性、可选功能、数据类型、转换和类型转换，以及各种运算符的详细规则。 **6. The OpenCL C Programming Language** **6.1 Unified Specification** OpenCL的核心部分提供了一个统一的编程语言，使得开发者可以编写可在不同设备上运行的代码，包括CPU、GPU和其他硬件加速器。这种跨平台兼容性是其主要优势，有助于简化软件开发流程。 **6.2 Optional Functionality** 除了基础功能，OpenCL还支持一些可选的功能模块，如特定设备或平台特有的扩展（6.2.2 Extensions），这些扩展允许开发者利用设备的独特性能优化特定应用场景。 **6.3 Supported Data Types** 数据类型是OpenCL编程的基础。它包括内置的标量类型（6.3.1 Built-in Scalar Data Types），如整型、浮点型和布尔型，以及向量数据类型（6.3.2 Built-in Vector Data Types），如`char2`, `float4`等。还有其他内建数据类型（6.3.3），如枚举和结构体，以及预留类型（6.3.4）供未来扩展使用。类型对齐（6.3.5）、向量字面量（6.3.6）、向量分量（6.3.7）、aliasing rules（6.3.8）和关键字（6.3.9）也是数据类型定义的重要组成部分。 **6.4 Conversions and Type Casting** OpenCL支持多种类型的转换，包括隐式转换（6.4.1），即在满足条件时自动进行的数据类型转换；显式转换（6.4.2）和显式重新解释数据类型（6.4.3），开发者可以明确指定转换过程；指针转换（6.4.5）用于在不同类型之间移动内存地址。此外，还有通常的算术转换规则（6.4.6），确保在运算时数据类型的兼容性。 **6.5 Operators** OpenCL的运算符分为多种类别：算术运算符（6.5.1）、一元运算符（6.5.2）、前缀和后缀运算符（6.5.3）、关系运算符（6.5.4）、相等运算符（6.5.5）、位操作符（6.5.6）以及逻辑运算符（6.5.7）。这些运算符用于执行基本数学运算、比较、逻辑判断等各种操作，是编写高效并行算法的关键。《OpenCL C编程语言规范》提供了详细的语法和规则，让开发者能够充分利用OpenCL的并行处理能力进行图像处理和其他高性能计算任务。通过理解这些内容，开发者可以写出兼容不同硬件设备的高效代码，并且遵循严格的语法规则，确保程序的正确性和性能。

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complex double, complex doublen A complex 64-bit floating-point scalar and

vector.

imaginary double, imaginary doublen An imaginary 64-bit floating-point scalar and

vector.

complex quad, complex quadn A complex 128-bit floating-point scalar and

vector.

imaginary quad, imaginary quadn An imaginary 128-bit floating-point scalar and

vector.

floatnxm

An n × m matrix of single precision floating-

point values stored in column-major order.

doublenxm

An n × m matrix of double precision floating-

point values stored in column-major order.

long double, long doublen A floating-point scalar and vector type with at

least as much precision and range as a

double

and no more precision and range than a quad.

long long, long longn

A 128-bit signed integer scalar and vector.

unsigned long long, ulong long, ulong longn A 128-bit unsigned integer scalar and vector.

6.3.5. 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, 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

vector data

load and store functions

vloadn, vload_halfn, vstoren, and vstore_halfn. 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.

6.3.6. Vector Literals

Vector literals can be used to create vectors from a list of scalars, vectors or a mixture thereof. A

vector literal can be used either as a vector initializer or as a primary expression. A vector literal

cannot be used as an l-value.

A vector literal is written as a parenthesized vector type followed by a parenthesized comma

delimited list of parameters. A vector literal operates as an overloaded function. The forms of the

function that are available is the set of possible argument lists for which all arguments have the

same element type as the result vector, and the total number of elements is equal to the number of

elements in the result vector. In addition, a form with a single scalar of the same type as the

element type of the vector is available. For example, the following forms are available for

float4:

(float4)( float, float, float, float )

(float4)( float2,

float, float )

(float4)(

float, float2, float )

(float4)(

float, float, float2 )

(float4)( float2, float2 )

(float4)( float3,

float )

(float4)(

float, float3 )

(float4)(

float )

Operands are evaluated by standard rules for function evaluation, except that implicit scalar

widening shall not occur. The order in which the operands are evaluated is undefined. The

operands are assigned to their respective positions in the result vector as they appear in memory

order. That is, the first element of the first operand is assigned to

result.x, the second element of

the first operand (or the first element of the second operand if the first operand was a scalar) is

assigned to

result.y, etc. In the case of the form that has a single scalar operand, the operand is

replicated across all lanes of the vector.

Examples:

float4 f = (float4)(1.0f, 2.0f, 3.0f, 4.0f);

uint4 u = (uint4)(

1); // u will be (1, 1, 1, 1).

float4 f = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));

float4 f = (float4)(

1.0f, (float2)(2.0f, 3.0f), 4.0f);

float4 f = (float4)(

1.0f, 2.0f); // error

6.3.7. Vector Components

The components of vector data types can be addressed as

<vector_data_type>.xyzw. Vector data

types with two or more components, such as

char2, can access .xy elements. Vector data types with

three or more components, such as

uint3, can access .xyz elements. Vector data types with four or

more components, such as

ulong4 or float8, can access .xyzw elements.

In OpenCL C 3.0, the components of vector data types can also be addressed as

<vector_data_type>.rgba. Vector data types with two or more components can access .rg elements.

Vector data types with three or more components can access

.rgb elements. Vector data types with

four or more components can access

.rgba elements.

Accessing components beyond those declared for the vector type is an error so, for example:

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