avoid the performance overhead of checking it every time. if godebug.Value("#ppc64aes") == "off" { supportsAES = false } impl.Register("aes", "POWER8", &supportsAES) } } // checkGenericIsExpect is called by the variable-time implementation to make // sure it is not used when hardware support is available. It shouldn't happen, // but this way it's more evidently correct. func checkGenericIsExpect() { if supportsAES { panic("crypto/aes: internal error: using generic implementation despite hardware support")...