From: Jonathan Tan <jonathantanmy@google•com>
To: Jonathan Tan via GitGitGadget <gitgitgadget@gmail•com>
Cc: Jonathan Tan <jonathantanmy@google•com>,
git@vger•kernel.org, gitster@pobox•com,
johannes.schindelin@gmx•de, peff@peff•net, ps@pks•im,
me@ttaylorr•com, johncai86@gmail•com, newren@gmail•com,
Derrick Stolee <stolee@gmail•com>
Subject: Re: [PATCH v2 1/8] pack-objects: create new name-hash function version
Date: Mon, 9 Dec 2024 15:15:22 -0800 [thread overview]
Message-ID: <20241209231522.841908-1-jonathantanmy@google.com> (raw)
In-Reply-To: <454b070d5bb0f64e11cab993b126ef5d37a3615b.1733181682.git.gitgitgadget@gmail.com>
"Jonathan Tan via GitGitGadget" <gitgitgadget@gmail•com> writes:
> diff --git a/pack-objects.h b/pack-objects.h
> index b9898a4e64b..15be8368d21 100644
> --- a/pack-objects.h
> +++ b/pack-objects.h
> @@ -207,6 +207,34 @@ static inline uint32_t pack_name_hash(const char *name)
> return hash;
> }
>
> +static inline uint32_t pack_name_hash_v2(const char *name)
> +{
> + uint32_t hash = 0, base = 0, c;
> +
> + if (!name)
> + return 0;
> +
> + while ((c = *name++)) {
> + if (isspace(c))
> + continue;
> + if (c == '/') {
> + base = (base >> 6) ^ hash;
> + hash = 0;
> + } else {
> + /*
> + * 'c' is only a single byte. Reverse it and move
> + * it to the top of the hash, moving the rest to
> + * less-significant bits.
> + */
> + c = (c & 0xF0) >> 4 | (c & 0x0F) << 4;
> + c = (c & 0xCC) >> 2 | (c & 0x33) << 2;
> + c = (c & 0xAA) >> 1 | (c & 0x55) << 1;
> + hash = (hash >> 2) + (c << 24);
> + }
> + }
> + return (base >> 6) ^ hash;
> +}
This works because `c` is masked before any arithmetic is performed on
it, but the cast from potentially signed char to uint32_t still makes
me nervous - if char is signed, it behaves as if it was first cast to
int32_t and only then to uint32_t, as you can see from running the code
below:
#include <stdio.h>
int main() {
signed char c = 128;
unsigned int u = c;
printf("hello %u\n", u);
return 0;
}
I would declare `c` as uint8_t or unsigned char.
next prev parent reply other threads:[~2024-12-09 23:15 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-05 3:05 [PATCH 0/7] pack-objects: Create an alternative name hash algorithm (recreated) Derrick Stolee via GitGitGadget
2024-11-05 3:05 ` [PATCH 1/7] pack-objects: add --full-name-hash option Derrick Stolee via GitGitGadget
2024-11-21 20:08 ` Taylor Blau
2024-11-21 21:35 ` Taylor Blau
2024-11-21 23:32 ` Junio C Hamano
2024-11-22 11:46 ` Derrick Stolee
2024-11-22 11:59 ` Derrick Stolee
2024-11-26 8:26 ` Patrick Steinhardt
2024-11-05 3:05 ` [PATCH 2/7] repack: " Derrick Stolee via GitGitGadget
2024-11-21 20:12 ` Taylor Blau
2024-11-22 12:07 ` Derrick Stolee
2024-11-05 3:05 ` [PATCH 3/7] pack-objects: add GIT_TEST_FULL_NAME_HASH Derrick Stolee via GitGitGadget
2024-11-21 20:15 ` Taylor Blau
2024-11-22 12:09 ` Derrick Stolee
2024-11-22 1:13 ` Jonathan Tan
2024-11-22 3:23 ` Junio C Hamano
2024-11-22 18:01 ` Jonathan Tan
2024-11-25 0:39 ` Junio C Hamano
2024-11-25 19:45 ` Jonathan Tan
2024-11-26 1:29 ` Junio C Hamano
2024-11-26 8:26 ` Patrick Steinhardt
2024-11-05 3:05 ` [PATCH 4/7] git-repack: update usage to match docs Derrick Stolee via GitGitGadget
2024-11-21 20:17 ` Taylor Blau
2024-11-22 15:26 ` Derrick Stolee
2024-11-05 3:05 ` [PATCH 5/7] p5313: add size comparison test Derrick Stolee via GitGitGadget
2024-11-21 20:31 ` Taylor Blau
2024-11-22 15:26 ` Derrick Stolee
2024-11-26 8:26 ` Patrick Steinhardt
2024-11-05 3:05 ` [PATCH 6/7] pack-objects: disable --full-name-hash when shallow Derrick Stolee via GitGitGadget
2024-11-21 20:33 ` Taylor Blau
2024-11-22 15:27 ` Derrick Stolee
2024-11-05 3:05 ` [PATCH 7/7] test-tool: add helper for name-hash values Derrick Stolee via GitGitGadget
2024-11-21 20:42 ` Taylor Blau
2024-11-22 1:23 ` Jonathan Tan
2024-11-21 23:50 ` [PATCH 0/7] pack-objects: Create an alternative name hash algorithm (recreated) Jonathan Tan
2024-11-22 3:01 ` Junio C Hamano
2024-11-22 4:22 ` Junio C Hamano
2024-11-22 15:27 ` Derrick Stolee
2024-11-24 23:57 ` Junio C Hamano
2024-11-22 18:05 ` Jonathan Tan
2024-12-02 23:21 ` [PATCH v2 0/8] " Derrick Stolee via GitGitGadget
2024-12-02 23:21 ` [PATCH v2 1/8] pack-objects: create new name-hash function version Jonathan Tan via GitGitGadget
2024-12-04 20:06 ` karthik nayak
2024-12-04 21:05 ` Junio C Hamano
2024-12-05 9:46 ` karthik nayak
2024-12-09 23:15 ` Jonathan Tan [this message]
2024-12-10 0:01 ` Junio C Hamano
2024-12-02 23:21 ` [PATCH v2 2/8] pack-objects: add --name-hash-version option Derrick Stolee via GitGitGadget
2024-12-04 20:53 ` karthik nayak
2024-12-02 23:21 ` [PATCH v2 3/8] repack: " Derrick Stolee via GitGitGadget
2024-12-04 21:15 ` karthik nayak
2024-12-02 23:21 ` [PATCH v2 4/8] pack-objects: add GIT_TEST_NAME_HASH_VERSION Derrick Stolee via GitGitGadget
2024-12-04 21:21 ` karthik nayak
2024-12-09 23:12 ` Jonathan Tan
2024-12-20 17:03 ` Derrick Stolee
2024-12-02 23:21 ` [PATCH v2 5/8] p5313: add size comparison test Derrick Stolee via GitGitGadget
2024-12-02 23:21 ` [PATCH v2 6/8] test-tool: add helper for name-hash values Derrick Stolee via GitGitGadget
2024-12-02 23:21 ` [PATCH v2 7/8] pack-objects: prevent name hash version change Derrick Stolee via GitGitGadget
2024-12-02 23:21 ` [PATCH v2 8/8] pack-objects: add third name hash version Derrick Stolee via GitGitGadget
2024-12-03 3:23 ` [PATCH v2 0/8] pack-objects: Create an alternative name hash algorithm (recreated) Junio C Hamano
2024-12-04 4:56 ` Derrick Stolee
2024-12-04 5:02 ` Junio C Hamano
2024-12-20 17:19 ` [PATCH v3 " Derrick Stolee via GitGitGadget
2024-12-20 17:19 ` [PATCH v3 1/8] pack-objects: create new name-hash function version Jonathan Tan via GitGitGadget
2025-01-22 22:08 ` Taylor Blau
2024-12-20 17:19 ` [PATCH v3 2/8] pack-objects: add --name-hash-version option Derrick Stolee via GitGitGadget
2025-01-22 22:17 ` Taylor Blau
2025-01-24 17:29 ` Derrick Stolee
2024-12-20 17:19 ` [PATCH v3 3/8] repack: " Derrick Stolee via GitGitGadget
2025-01-22 22:18 ` Taylor Blau
2024-12-20 17:19 ` [PATCH v3 4/8] pack-objects: add GIT_TEST_NAME_HASH_VERSION Derrick Stolee via GitGitGadget
2025-01-22 22:20 ` Taylor Blau
2024-12-20 17:19 ` [PATCH v3 5/8] p5313: add size comparison test Derrick Stolee via GitGitGadget
2024-12-20 17:19 ` [PATCH v3 6/8] test-tool: add helper for name-hash values Derrick Stolee via GitGitGadget
2024-12-20 17:19 ` [PATCH v3 7/8] pack-objects: prevent name hash version change Derrick Stolee via GitGitGadget
2025-01-22 22:22 ` Taylor Blau
2024-12-20 17:19 ` [PATCH v3 8/8] pack-objects: add third name hash version Derrick Stolee via GitGitGadget
2025-01-22 22:37 ` Taylor Blau
2025-01-24 17:34 ` Derrick Stolee
2025-01-21 20:21 ` [PATCH v3 0/8] pack-objects: Create an alternative name hash algorithm (recreated) Derrick Stolee
2025-01-22 23:28 ` Taylor Blau
2025-01-24 17:45 ` Derrick Stolee
2025-01-27 19:02 ` [PATCH v4 0/7] " Derrick Stolee via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 1/7] pack-objects: create new name-hash function version Jonathan Tan via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 2/7] pack-objects: add --name-hash-version option Derrick Stolee via GitGitGadget
2025-01-27 21:18 ` Junio C Hamano
2025-01-29 13:38 ` Derrick Stolee
2025-01-27 19:02 ` [PATCH v4 3/7] repack: " Derrick Stolee via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 4/7] pack-objects: add GIT_TEST_NAME_HASH_VERSION Derrick Stolee via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 5/7] p5313: add size comparison test Derrick Stolee via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 6/7] test-tool: add helper for name-hash values Derrick Stolee via GitGitGadget
2025-01-27 19:02 ` [PATCH v4 7/7] pack-objects: prevent name hash version change Derrick Stolee via GitGitGadget
2025-01-31 21:39 ` [PATCH v4 0/7] pack-objects: Create an alternative name hash algorithm (recreated) Taylor Blau
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