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    SubjectRe: [PATCH net-next v5 03/20] zinc: ChaCha20 generic C implementation and selftest
    On Wed, Sep 19, 2018 at 3:08 AM Eric Biggers <ebiggers@kernel.org> wrote:
    > Does this consistently perform as well as an implementation that organizes the
    > operations such that the quarterrounds for all columns/diagonals are
    > interleaved? As-is, there are tight dependencies in QUARTER_ROUND() (as well as
    > in the existing chacha20_block() in lib/chacha20.c, for that matter), so we're
    > heavily depending on the compiler to do the needed interleaving so as to not get
    > potentially disastrous performance. Making it explicit could be a good idea.

    It does perform as well, and the compiler outputs good code, even on
    older compilers. Notably that's all a single statement (via the comma
    operator).

    > > +}
    > > +
    > > +static void chacha20_generic(u8 *out, const u8 *in, u32 len, const u32 key[8],
    > > + const u32 counter[4])
    > > +{
    > > + __le32 buf[CHACHA20_BLOCK_WORDS];
    > > + u32 x[] = {
    > > + EXPAND_32_BYTE_K,
    > > + key[0], key[1], key[2], key[3],
    > > + key[4], key[5], key[6], key[7],
    > > + counter[0], counter[1], counter[2], counter[3]
    > > + };
    > > +
    > > + if (out != in)
    > > + memmove(out, in, len);
    > > +
    > > + while (len >= CHACHA20_BLOCK_SIZE) {
    > > + chacha20_block_generic(buf, x);
    > > + crypto_xor(out, (u8 *)buf, CHACHA20_BLOCK_SIZE);
    > > + len -= CHACHA20_BLOCK_SIZE;
    > > + out += CHACHA20_BLOCK_SIZE;
    > > + }
    > > + if (len) {
    > > + chacha20_block_generic(buf, x);
    > > + crypto_xor(out, (u8 *)buf, len);
    > > + }
    > > +}
    >
    > If crypto_xor_cpy() is used instead of crypto_xor(), and 'in' is incremented
    > along with 'out', then the memmove() is not needed.

    Nice idea, thanks. Implemented.

    Jason

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