Vector Class Discussion

This library has much more features than Intel's vector classes:

Features

• vectors of 8, 16, 32 and 64-bit integers, signed and unsigned
• vectors of single and double precision floating point numbers
• total vector size 128 or 256 bits
• defines almost all common operators
• boolean operations and branches on vector elements
• defines many arithmetic functions
• permute, blend and table-lookup functions
• fast integer division
• many mathematical functions (requires external library)
• can build code for different instruction sets from the same source code
• CPU dispatching to utilize higher instruction sets when available
• uses metaprogramming (including preprocessing directives and templates) to find the best implementation for the selected instruction set and parameter values of a given operator or function

Take a look at www.agner.org/optimize/#vectorclass and have fun!

Nice work, but, frankly, this library should have been released somewhen in 1998-99, when AMD and Intel have released their first CPUs with 3DNow! and SSE, respectively. Nowadays, OpenCL is much more relevant.

OpenCL is a cross-platform language while my vector class library is carefully tweaked to the x86 and x86-64 instruction set extensions SSE2 through AVX2. It is intended as a tool to make it easier to use these specific instruction set extensions and get the maximum performance out of them without adding any extra runtime overhead. It works with some of the best optimizing C++ compilers available and can be combined with existing C++ code.

The advantage of OpenCL is that it can utilize the GPU. The main disadvantage is that it is a separate programming language and it doesn't have C++ constructs. A cross-platform language always has to make compromises for the sake of generality and portability.

OpenCL allows you to use types and vector sizes that don't fit the hardware registers. It even allows you to use types that work poorly on a specific platform, such as double precision on platforms that support only single precision.

In conclusion, OpenCL and my vector class library serve very different purposes.

Nice work, but, frankly, this library should have been released somewhen in 1998-99, when AMD and Intel have released their first CPUs with 3DNow! and SSE, respectively. Nowadays, OpenCL is much more relevant.

It won't die out overnight, but OpenCL can only evolve into a fully unrestricted generic programming language. The ironic part is we already have that; it's called C! So why not skip that awkward "evolution to the past", and just use vectorizing compilers? With AVX2 they'll be much more effective than ever before since the gather instruction enables the same kind of parallelization as what's done on the GPU. And it can support many more languages than just C.

So I'm afraid OpenCL is a new standard where none was needed. We just needed homogeneous high throughput computing instruction set extensions like AVX2.

OpenCL might actually be short-lived once AVX2 processors become available.

BTW. My vector class library supports AVX2.

The GPU is still much faster than a CPU with AVX2, so OpenCL will still be useful for some purposes with massively parallel data.

So the raw computing power is a bad indicator for effective performance. It will be much easier to achieve good performance out of AVX2.

BTW. My vector class library supports AVX2.

Agner wrote:

The GPU is still much faster than a CPU with AVX2, so OpenCL will still be useful for some purposes with massively parallel data.

I don't think that's generally true. A quad-core Haswell GT2 chip will have close to 500 GFLOPS on the CPU side, but only about 400 GFLOPS on the GPU side. Also, homogeneous computing is inherently more efficient due to requiring less data movement. And a GPU can easily stall due to a lack of out-of-order execution, insufficient parallelism, register space limits, and/or (shared) data bandwidth bottlenecks. The GTX 680 (3 TFLOPS) even fails to outperform an i7-3820 (230 GFLOPS): LuxMark OpenCL rendering!

So the raw computing power is a bad indicator for effective performance. It will be much easier to achieve good performance out of AVX2.