【arm】armv8中通用寄存器的饱和指令实现（对标arm32：ssat,usat,qadd,qsub）

Date: 2018.9.7

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1、参考：

https://community.arm.com/processors/f/discussions/3330/how-aarch32-bit-applications-will-be-supported-on-aarch64
https://community.arm.com/processors/f/discussions/7521/what-is-the-equivalent-instruction-for-qsub-in-armv8
https://community.arm.com/iot/embedded/f/discussions/124/how-to-implement-saturation-instructions-in-armv8-architecture?ReplySortBy=Votes&ReplySortOrder=Descending

2、armv8与aarch32指令集的重要差异

In AArch64, there are no SIMD or saturating arithmetic instructions which operate on general-purpose registers.Such operations use the NEON registers.

QADD,QSUB,SSAT，USAT等饱和指令在ARMv8中不支持，即没有通用寄存器的饱和指令。

ARM32中的SWP指令在ARMv8中也不支持。

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THE END!