SIMD intrinsics are less C and more assembly with overlong mnemonics and a register allocator, so even reading them is something of a separate skill. Unlike the skill of achieving meaningful speedups by writing them (i.e. low-level optimization), it’s nothing special, but expect to spend a lot of time jumping between the code and the reference manuals[1,2] at first.

[1] https://www.intel.com/content/www/us/en/docs/intrinsics-guid...

[2] https://developer.arm.com/architectures/instruction-sets/int...