Editing ARM architecture family (section)

==={{anchor|NEON}}{{anchor|Advanced SIMD (NEON)}}Advanced SIMD (Neon)===
The ''Advanced SIMD'' extension (also known as ''Neon'' or "MPE" Media Processing Engine) is a combined 64- and [[128-bit computing|128-bit]] SIMD instruction set that provides standardised acceleration for media and signal processing applications. Neon is included in all Cortex-A8 devices, but is optional in Cortex-A9 devices.<ref>{{cite web |url=https://www.arm.com/products/processors/cortex-a/cortex-a9.php |title=Cortex-A9 Processor |website=arm.com |access-date=21 November 2011}}</ref> Neon can execute MP3 audio decoding on CPUs running at 10&nbsp;MHz, and can run the [[GSM]] [[adaptive Multi-Rate audio codec|adaptive multi-rate]] (AMR) speech codec at 13&nbsp;MHz. It features a comprehensive instruction set, separate register files, and independent execution hardware.<ref>{{cite web |url=http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0409f/Chdceejc.html |title=About the Cortex-A9 NEON MPE |website=arm.com |access-date=21 November 2011}}</ref> Neon supports 8-, 16-, 32-, and 64-bit integer and single-precision (32-bit) floating-point data and SIMD operations for handling audio and video processing as well as graphics and gaming processing. In Neon, the SIMD supports up to 16&nbsp;operations at the same time. The Neon hardware shares the same floating-point registers as used in VFP. Devices such as the ARM Cortex-A8 and Cortex-A9 support 128-bit vectors, but will execute with 64&nbsp;bits at a time,<ref name="cortex_a9"/> whereas newer Cortex-A15 devices can execute 128&nbsp;bits at a time.<ref>{{cite web |url=https://patents.google.com/patent/US20050125476A1/en |title=US20050125476A1}}</ref><ref>{{cite web |url=https://patents.google.com/patent/US20080141004A1/en |title=US20080141004A1}}</ref>

A quirk of Neon in Armv7 devices is that it flushes all [[subnormal number]]s to zero, and as a result the [[GNU Compiler Collection|GCC]] compiler will not use it unless {{code|-funsafe-math-optimizations}}, which allows losing denormals, is turned on. "Enhanced" Neon defined since Armv8 does not have this quirk, but as of {{nowrap|GCC 8.2}} the same flag is still required to enable Neon instructions.<ref>{{cite web |title=ARM Options |url=https://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html |website=GNU Compiler Collection Manual |access-date=20 September 2019}}</ref> On the other hand, GCC does consider Neon safe on AArch64 for Armv8.

ProjectNe10 is ARM's first open-source project (from its inception; while they acquired an older project, now named [[Mbed TLS]]<!--the sub-project https://github.com/ARMmbed/mbed-crypto seems to have only x86 assembly-->). The Ne10 library is a set of common, useful functions written in both Neon and C (for compatibility). The library was created to allow developers to use Neon optimisations without learning Neon, but it also serves as a set of highly optimised Neon intrinsic and assembly code examples for common DSP, arithmetic, and image processing routines. The source code is available on GitHub.<ref>{{GitHub|projectNe10/Ne10|Ne10: An open optimized software library project for the ARM Architecture}}</ref>