问题
What is the difference between NEON SIMD and NEON SIMD version 2 as in Cortex A15?
回答1:
It adds SIMD FMA instruction (VFMA.F32) and also mandates NEON half precision extension. NEONv2 is supported in ARM Cortex-A7, ARM Cortex-A15, and Qualcomm Krait (not sure about ARM Cortex-A5).
回答2:
It is not that much of a difference, from ARM ARM:
(in reverse order of definitions)
Advanced SIMDv2 is an OPTIONAL extension to the ARMv7-A and ARMv7-R profiles. Advanced SIMDv2 adds both the Half-precision Extension and the fused multiply-add instructions to the features of Advanced SIMDv1.
...
Advanced SIMDv1 can be extended by the OPTIONAL Half-precision Extension, that provides conversion functions in both directions between half-precision floating-point and single-precision floating-point.
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The Advanced SIMD architecture extension, its associated implementations, and supporting software, are commonly referred to as NEON™ technology.
来源：https://stackoverflow.com/questions/15227278/arm-neon-simd-version-2