Fast byte searching with SIMD without a ton of boilerplate?

TL;DR: I’m looking for a SIMD abstraction layer that will let me do some high-speed byte searching without having to worry about a dozen different instruction sets. Not having luck finding such.

I’m optimizing some JSON-parsing code, and by far the biggest bottleneck is string searching, specifically searching for the next occurrence of one of two or more characters. For example, when scanning a string I search for both double-quote and backslash. (Plus 00 if the JSON has not been validated.)

• C has a function to do this, strcspn, but it’s slow.
• A naive loop testing every char with several == comparisons is faster.
• indexing each byte in a 256-item lookup table is still faster.
• Unrolling the loop to look at 4 bytes in sequence is even faster (stole this from sa-json.)
• “Homemade SIMD” by reading a uint32 or uint64 and doing bitwise tricks to detect any of those bytes is significantly slower, sadly.
• [Goldilocks solution goes here]
• The SIMDJSON library is super fast but has a whole bunch of complex code — it has to implement the core loops six or seven times for specific instruction sets, and then figure out at runtime which of those to call. I would rather avoid dragging all that in.

Yesterday I was experimenting with Apple’s “simd” library, which is based on Clang vector extensions, and it does pretty well, but I am not sure if this is portable to non-Apple systems or non-Clang compilers. (GCC has its own extensions, which Clang partially supports, but when I tried those Clang generated slow non-SIMD code.)