64-bit x86 CPUs are defined to support SSE2 as a minimum, and all 64-bit operating systems use it by default. For 32-bit systems, you still theoretically have

64-bit x86 CPUs are defined to support SSE2 as a minimum, and all 64-bit operating systems use it by default. For 32-bit systems, you still theoretically have to check, but I think every halfway modern compiler also uses SSE2 as the default target.