Re: [Qemu-devel] [PATCH 4/6] crypto: convert xts_tweak_encdec to use xts_uint128 type

[Alberto Garcia]

On Tue 09 Oct 2018 02:55:39 PM CEST, Daniel P. Berrangé wrote:
> Using 64-bit arithmetic increases the performance for xts-aes-128
> when built with gcrypt:
>
>   Encrypt: 235 MB/s -> 320 MB/s
>   Decrypt: 245 MB/s -> 325 MB/s
>
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
>  crypto/xts.c | 52 +++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 33 insertions(+), 19 deletions(-)
>
> diff --git a/crypto/xts.c b/crypto/xts.c
> index ded4365191..f109c8a3ee 100644
> --- a/crypto/xts.c
> +++ b/crypto/xts.c
> @@ -31,6 +31,12 @@ typedef struct {
>      uint64_t b;
>  } xts_uint128;
>  
> +#define xts_uint128_xor(D, S1, S2)              \
> +    do {                                        \
> +        (D)->a = (S1)->a ^ (S2)->a;             \
> +        (D)->b = (S1)->b ^ (S2)->b;             \
> +    } while (0)
> +
>  static void xts_mult_x(uint8_t *I)
>  {
>      int x;
> @@ -59,25 +65,19 @@ static void xts_mult_x(uint8_t *I)
>   */
>  static void xts_tweak_encdec(const void *ctx,
>                               xts_cipher_func *func,
> -                             const uint8_t *src,
> -                             uint8_t *dst,
> -                             uint8_t *iv)
> +                             const xts_uint128 *src,
> +                             xts_uint128 *dst,
> +                             xts_uint128 *iv)
>  {
> -    unsigned long x;
> -
>      /* tweak encrypt block i */
> -    for (x = 0; x < XTS_BLOCK_SIZE; x++) {
> -        dst[x] = src[x] ^ iv[x];
> -    }
> +    xts_uint128_xor(dst, src, iv);
>  
> -    func(ctx, XTS_BLOCK_SIZE, dst, dst);
> +    func(ctx, XTS_BLOCK_SIZE, (uint8_t *)dst, (uint8_t *)dst);

In the line of what I said earlier, perhaps it's clearer if you leave
everything as uint8_t * and simply make xts_uint128_xor() treat the
array as xts_uint128 internally.

>      for (i = 0; i < lim; i++) {
> -        xts_tweak_encdec(datactx, decfunc, src, dst, (uint8_t *)&T);
> +        xts_uint128 S, D;
> +
> +        memcpy(&S, src, XTS_BLOCK_SIZE);
> +        xts_tweak_encdec(datactx, decfunc, &S, &D, &T);
> +        memcpy(dst, &D, XTS_BLOCK_SIZE);

Why do you need S and D?

Berto