Re: [PATCH 1/3] random: replace non-blocking pool with a Chacha20-based CRNG

[Jeffrey Walton]

> +static inline u32 rotl32(u32 v, u8 n)
> +{
> +       return (v << n) | (v >> (sizeof(v) * 8 - n));
> +}

That's undefined behavior when n=0.

I think the portable way to do a rotate that avoids UB is the
following. GCC, Clang and ICC recognize the pattern, and emit a rotate
instruction.

    static const unsigned int MASK=31;
    return (v<<n)|(v>>(-n&MASK));

You should also avoid the following because its not constant time due
to the branch:

    return n == 0 ? v : (v << n) | (v >> (sizeof(v) * 8 - n));

Jeff