How about adding another sentence "This, 3 is representable exactly as 0x3p0 or 0x6p-1 or 0xcp-2, but if the first hexadecimal digit is limited to 1, then 3 can only be approximated by 0x1p+1 or 0x1p+2, depending on rounding direction." A single sentence footnote is rapidly exploding into a paragraph.