On Wed, 20 Feb 2019, Warren D Smith wrote: > but if I try to replace that with the nicer (since more portable) > c = __builtin_shuffle(a, b); > then > error: use of unknown builtin '__builtin_shuffle' > [-Wimplicit-function-declaration]
Most likely you're on OS X and the 'gcc' command actually invokes Clang/LLVM. Clang does not implement this builtin (there's __builtin_shufflevector with a different interface — see Clang documentation for details). Alexander
