Do unsigned integral types satisfy RandomAccessIterable?

[ericniebler]

Required expression i += n where n is the (signed) difference type. To evaluate, n is first converted to unsigned ([conv.integral]):

If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2n where n is the number of bits used to represent the unsigned type). [ Note: In a two’s complement representation, this conversion is conceptual and there is no change in the bit pattern (if there is no truncation). —end note ]

Any sane semantics for RandomAccessIterable would give the result of i += n the same result as n applications of ++i (or of -n applications of --i if n is negative). I need to sit down and characterize the situations in which that is not true (if any).

Note that for a type like unsigned char, given the way difference_type_t is defined in the Ranges TS, the difference type will likely have more bits than unsigned char.