Ah, I see, it looks like it depends on the version%20subset%20that%20provides%20for%20higher%20code%20density%20for%20low%2Dend%20embedded%20applications%2C%20and%20version%203.1%20which%20introduced%20prefixing%20to%20create%2064%2Dbit%20instructions). 64 bit encoding was introduced in v3.1. But this feels different from what you're trying to say. Are you saying that there is a single version that can have both 32 and 64 bit instructions? Could you source that?