Editing Vector processor (section)

=== GPU vector processing features ===

With many 3D [[shader]] applications needing [[trigonometric]] operations as well as short vectors for common operations (RGB, ARGB, XYZ, XYZW) support for the following is typically present in modern GPUs, in addition to those found in vector processors:

* '''Sub-vectors''' – elements may typically contain two, three or four sub-elements (vec2, vec3, vec4) where any given bit of a predicate mask applies to the whole vec2/3/4, not the elements in the sub-vector. Sub-vectors are also introduced in RISC-V RVV (termed "LMUL").<ref>[https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#mapping-for-lmul-1-2 LMUL > 1 in RVV]</ref> Subvectors are a critical integral part of the [[Vulkan]] [[SPIR-V]] spec.
* '''Sub-vector Swizzle''' – aka "Lane Shuffling" which allows sub-vector inter-element computations without needing extra (costly, wasteful) instructions to move the sub-elements into the correct SIMD "lanes" and also saves predicate mask bits. Effectively an in-flight [[permute instruction|mini-permute]] of the sub-vector, this heavily features in 3D Shader binaries and is sufficiently important as to be part of the Vulkan SPIR-V spec. The Broadcom [[Videocore]] IV uses the terminology "Lane rotate"<ref>[https://patents.google.com/patent/US20110227920 Abandoned US patent US20110227920-0096]</ref> where the rest of the industry uses the term [[Swizzling (computer graphics)|"swizzle"]].<ref>[https://github.com/hermanhermitage/videocoreiv-qpu Videocore IV QPU]</ref>
* '''Transcendentals''' – [[trigonometric]] operations such as [[sine]], [[cosine]] and [[logarithm]] obviously feature much more predominantly in 3D than in many demanding [[High-performance computing|HPC]] workloads. Of interest, however, is that speed is far more important than accuracy in 3D for GPUs, where computation of pixel coordinates simply do not require high precision. The Vulkan specification recognises this and sets surprisingly low accuracy requirements, so that GPU Hardware can reduce power usage. The concept of reducing accuracy where it is simply not needed is explored in the [[MIPS-3D]] extension.