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From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: "Todd Zullinger" <tmz@pobox.com>, "René Scharfe" <l.s.r@web.de>,
	"Randall S. Becker" <rsbecker@nexbridge.com>,
	"Christian Couder" <chriscool@tuxfamily.org>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	git@vger.kernel.org, git-packagers@googlegroups.com
Subject: Re: [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop
Date: Tue, 30 Jul 2019 13:39:48 -0700	[thread overview]
Message-ID: <xmqqpnlrs1d7.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20190730200203.GA4882@sigill.intra.peff.net> (Jeff King's message of "Tue, 30 Jul 2019 16:02:03 -0400")

Jeff King <peff@peff.net> writes:

> @@ -116,19 +116,11 @@ unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
>   * Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
>   * for use in hash tables. Cryptographic hashes are supposed to have
>   * uniform distribution, so in contrast to `memhash()`, this just copies
> - * the first `sizeof(int)` bytes without shuffling any bits. Note that
> - * the results will be different on big-endian and little-endian
> - * platforms, so they should not be stored or transferred over the net.

;-)

> + * the first `sizeof(int)` bytes without shuffling any bits.
>   */
>  static inline unsigned int oidhash(const struct object_id *oid)
>  {
> -	/*
> -	 * Equivalent to 'return *(unsigned int *)oid->hash;', but safe on
> -	 * platforms that don't support unaligned reads.
> -	 */
> -	unsigned int hash;
> -	memcpy(&hash, oid->hash, sizeof(hash));
> -	return hash;
> +	return get_be32(oid->hash);
>  }
>  
>  /*
> diff --git a/t/t0016-oidmap.sh b/t/t0016-oidmap.sh
> index bbe719e950..6656db9d69 100755
> --- a/t/t0016-oidmap.sh
> +++ b/t/t0016-oidmap.sh
> @@ -93,9 +93,9 @@ put three 3
>  iterate" "NULL
>  NULL
>  NULL
> +$(git rev-parse three) 3
>  $(git rev-parse two) 2
> -$(git rev-parse one) 1
> -$(git rev-parse three) 3"
> +$(git rev-parse one) 1"
>  
>  '
>
> which not only fixes this test but any other hash-based oddities. I
> wonder if it's appreciably less efficient. I'll bet I could nerd-snipe
> René into doing a bunch of measurements and explorations of the
> disassembled code. ;)

I'd rather see us go in the direction of discouraging people from
relying on the hash order.

  reply	other threads:[~2019-07-30 20:39 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 17:08 [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop Randall S. Becker
2019-07-30 17:31 ` Junio C Hamano
2019-07-30 18:09   ` Matheus Tavares Bernardino
2019-07-30 18:10   ` Randall S. Becker
2019-07-30 18:35     ` Junio C Hamano
2019-07-30 19:45 ` Jeff King
2019-07-30 20:25   ` Randall S. Becker
2019-07-30 19:49 ` Todd Zullinger
2019-07-30 20:02   ` Jeff King
2019-07-30 20:39     ` Junio C Hamano [this message]
2019-07-30 20:56     ` SZEDER Gábor
2019-07-31  0:59       ` Jeff King
2019-07-31  1:23         ` Jeff King
2019-07-31  1:27           ` Jeff King
2019-07-31  1:59           ` Todd Zullinger
2019-07-31  3:27             ` Jeff King
2019-07-31  3:53               ` Jeff King
2019-07-31 17:17                 ` Junio C Hamano
2019-07-31 21:22                   ` non-cryptographic hash algorithms in git Jeff King
2019-07-31  4:06               ` [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop René Scharfe
2019-07-31  4:30                 ` Jeff King
2019-07-31  6:04               ` Todd Zullinger
2019-07-31 16:57         ` Junio C Hamano
2019-07-30 20:27   ` Randall S. Becker

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