Re: [PATCH] sha256: add support for Nettle

[Jeff King <peff@peff.net>]

On Tue, Jul 05, 2022 at 11:05:18PM +0000, brian m. carlson wrote:

> Let's add another option that's compatible with the GPLv2, which is
> Nettle.  It also has recently gained support for Intel's SHA-NI
> instructions, which compare very favorably to other implementations.
> For example, using this implementation and SHA-1 DC on a machine with
> SHA-NI, hashing a 2 GiB file with SHA-1 takes 7.582 seconds, while
> hashing the same file with SHA-256 takes 2.278 seconds.

Nifty. I was curious about the speed on my machine, since I still had
that sha256 import of linux.git. Sadly, it's not nearly as impressive:

  [blk_sha256]
  $ time git index-pack --verify objects/pack/*.pack
  real	2m40.164s
  user	12m30.626s
  sys	0m31.567s

  [nettle]
  $ time git index-pack --verify objects/pack/*.pack
  real	2m21.346s
  user	10m14.507s
  sys	0m30.943s

which I take to mean that it doesn't support the Intel SHA extensions
(and /proc/cpuinfo confirms that). Still, 12-18% speedup is a nice and
easy win.

>  Makefile        |  7 +++++++
>  hash.h          |  4 +++-
>  sha256/nettle.h | 28 ++++++++++++++++++++++++++++
>  3 files changed, 38 insertions(+), 1 deletion(-)
>  create mode 100644 sha256/nettle.h

The patch itself looks good to me, modulo the guard typo already pointed
out.

-Peff