mul in the function name is a hint that this intrinsic uses the
MUL instruction. Based on the types of the arguments and return value, sixteen bytes of signed integers, we might guess this intrinsic maps to the following instruction:
MUL Vd.16B, Vn.16B, Vm.16B
So this function multiplies corresponding elements of
b and returns the result. Checking the definition shows this is indeed true.