From: Jeff King <peff@peff•net>
To: Taylor Blau <me@ttaylorr•com>
Cc: Patrick Steinhardt <ps@pks•im>,
Junio C Hamano <gitster@pobox•com>,
git@vger•kernel.org, Elijah Newren <newren@gmail•com>
Subject: Re: [PATCH v2 11/18] git-compat-util.h: introduce `u32_add()`
Date: Mon, 23 Feb 2026 08:49:35 -0500 [thread overview]
Message-ID: <20260223134935.GA271392@coredump.intra.peff.net> (raw)
In-Reply-To: <aXFni2tE7vn1dKFp@nand.local>
On Wed, Jan 21, 2026 at 06:55:55PM -0500, Taylor Blau wrote:
> I had considered this approach when writing, but ultimately decided
> against it, since it felt a little clunky to have to pass a pointer in
> to do a simple arithmetic operation. But I think your point about
> ensuring that we actually do:
>
> if (unsigned_mult_overflows(a, b))
> die(...);
> result = a * b;
>
> and not "result = a * c" or some other expression which is not "a * b"
> is a good one.
It is clunky, but it's how the compiler intrinsics work (if we ever
chose to use them).
> I dunno. The spots in this patch are the only uses of u64_mult() and
> u64_add(), so I'm hesitant to keep a helper function around just for
> that sole use-case. I wonder if we should do what you suggest here for
> the much more frequently used st_add() / st_mult() / st_sub() functions?
I am to blame for the crappy interface of the st_add() etc functions. It
did make conversion _much_ easier, because you can do stuff like:
-foo = malloc(nr * size);
+foo = malloc(st_mult(nr, size));
as opposed to:
size_t total;
...
st_mult(&total, nr, size));
foo = malloc(total);
My rationale was that size_t computations like this are OK to die() with
very little useful error reporting up the chain because:
1. The result is generally just passed along to malloc() anyway, where
we likewise find it OK to die() without much info. So you can
imagine a world where we just do 128-bit size computations and then
let malloc() fail, and it would look the same. ;)
2. They don't happen in practice unless there is a bug or a malicious
input. Which is mostly true for 64-bit systems. Maybe less so for
32-bit ones, where you might conceivably wish to have 4 billion of
something.
I don't think any of that holds true for u32 values like counts of
objects. It's conceivable that you might want to try to write a midx for
two packs with 2.1 billion objects each (though from my experience, such
a repo would be unusable).
Anyway. My point is mostly that I think we can design u32_add() to be
what we want and not worry too much about going back to fix st_add(),
etc.
-Peff
next prev parent reply other threads:[~2026-02-23 13:49 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-06 20:30 [PATCH 00/17] midx: incremental MIDX/bitmap layer compaction Taylor Blau
2025-12-06 20:31 ` [PATCH 01/17] midx: mark `get_midx_checksum()` arguments as const Taylor Blau
2025-12-08 18:26 ` Patrick Steinhardt
2025-12-09 1:41 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 02/17] midx: split `get_midx_checksum()` by adding `get_midx_hash()` Taylor Blau
2025-12-08 18:25 ` Patrick Steinhardt
2025-12-09 1:42 ` Taylor Blau
2025-12-09 1:50 ` Taylor Blau
2025-12-09 6:27 ` Patrick Steinhardt
2026-01-13 22:46 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 03/17] builtin/multi-pack-index.c: make '--progress' a common option Taylor Blau
2025-12-06 20:31 ` [PATCH 04/17] git-multi-pack-index(1): remove non-existent incompatibility Taylor Blau
2025-12-06 20:31 ` [PATCH 05/17] git-multi-pack-index(1): align SYNOPSIS with 'git multi-pack-index -h' Taylor Blau
2025-12-06 20:31 ` [PATCH 06/17] t/t5319-multi-pack-index.sh: fix copy-and-paste error in t5319.39 Taylor Blau
2025-12-06 20:31 ` [PATCH 07/17] midx-write.c: don't use `pack_perm` when assigning `bitmap_pos` Taylor Blau
2025-12-08 18:26 ` Patrick Steinhardt
2025-12-09 1:59 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 08/17] midx-write.c: introduce `struct write_midx_opts` Taylor Blau
2025-12-08 18:26 ` Patrick Steinhardt
2025-12-09 2:04 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 09/17] midx: do not require packs to be sorted in lexicographic order Taylor Blau
2025-12-08 18:26 ` Patrick Steinhardt
2025-12-09 2:07 ` Taylor Blau
2025-12-09 2:11 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 10/17] git-compat-util.h: introduce `u32_add()` Taylor Blau
2025-12-08 18:27 ` Patrick Steinhardt
2025-12-09 2:13 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 11/17] midx-write.c: introduce `midx_pack_perm()` helper Taylor Blau
2025-12-06 20:31 ` [PATCH 12/17] midx-write.c: extract `fill_pack_from_midx()` Taylor Blau
2025-12-06 20:31 ` [PATCH 13/17] midx-write.c: enumerate `pack_int_id` values directly Taylor Blau
2025-12-08 18:27 ` Patrick Steinhardt
2025-12-09 2:14 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 14/17] midx-write.c: factor fanout layering from `compute_sorted_entries()` Taylor Blau
2025-12-06 20:31 ` [PATCH 15/17] t/helper/test-read-midx.c: plug memory leak when selecting layer Taylor Blau
2025-12-08 18:27 ` Patrick Steinhardt
2025-12-09 2:16 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 16/17] midx: implement MIDX compaction Taylor Blau
2025-12-09 7:21 ` Patrick Steinhardt
2026-01-13 23:32 ` Taylor Blau
2025-12-06 20:31 ` [PATCH 17/17] midx: enable reachability bitmaps during " Taylor Blau
2025-12-09 7:21 ` Patrick Steinhardt
2026-01-13 23:47 ` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 00/18] midx: incremental MIDX/bitmap layer compaction Taylor Blau
2026-01-14 19:54 ` [PATCH v2 01/18] midx: mark `get_midx_checksum()` arguments as const Taylor Blau
2026-01-14 19:54 ` [PATCH v2 02/18] midx: rename `get_midx_checksum()` to `midx_get_checksum_hash()` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 03/18] midx: introduce `midx_get_checksum_hex()` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 04/18] builtin/multi-pack-index.c: make '--progress' a common option Taylor Blau
2026-01-14 19:54 ` [PATCH v2 05/18] git-multi-pack-index(1): remove non-existent incompatibility Taylor Blau
2026-01-14 19:54 ` [PATCH v2 06/18] git-multi-pack-index(1): align SYNOPSIS with 'git multi-pack-index -h' Taylor Blau
2026-01-14 19:54 ` [PATCH v2 07/18] t/t5319-multi-pack-index.sh: fix copy-and-paste error in t5319.39 Taylor Blau
2026-01-14 19:54 ` [PATCH v2 08/18] midx-write.c: don't use `pack_perm` when assigning `bitmap_pos` Taylor Blau
2026-01-14 21:13 ` Junio C Hamano
2026-01-14 21:40 ` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 09/18] midx-write.c: introduce `struct write_midx_opts` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 10/18] midx: do not require packs to be sorted in lexicographic order Taylor Blau
2026-01-14 21:28 ` Junio C Hamano
2026-01-14 21:44 ` Taylor Blau
2026-01-27 7:34 ` Patrick Steinhardt
2026-02-24 18:47 ` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 11/18] git-compat-util.h: introduce `u32_add()` Taylor Blau
2026-01-14 21:49 ` Junio C Hamano
2026-01-14 22:03 ` Taylor Blau
2026-01-15 0:11 ` Taylor Blau
2026-01-21 8:51 ` Patrick Steinhardt
2026-01-21 23:55 ` Taylor Blau
2026-01-22 2:26 ` rsbecker
2026-01-22 17:07 ` Junio C Hamano
2026-02-23 13:49 ` Jeff King [this message]
2026-02-24 18:53 ` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 12/18] midx-write.c: introduce `midx_pack_perm()` helper Taylor Blau
2026-01-14 19:54 ` [PATCH v2 13/18] midx-write.c: extract `fill_pack_from_midx()` Taylor Blau
2026-01-14 19:54 ` [PATCH v2 14/18] midx-write.c: enumerate `pack_int_id` values directly Taylor Blau
2026-01-14 19:55 ` [PATCH v2 15/18] midx-write.c: factor fanout layering from `compute_sorted_entries()` Taylor Blau
2026-01-14 19:55 ` [PATCH v2 16/18] t/helper/test-read-midx.c: plug memory leak when selecting layer Taylor Blau
2026-01-14 19:55 ` [PATCH v2 17/18] midx: implement MIDX compaction Taylor Blau
2026-01-27 7:35 ` Patrick Steinhardt
2026-01-27 22:13 ` Taylor Blau
2026-01-14 19:55 ` [PATCH v2 18/18] midx: enable reachability bitmaps during " Taylor Blau
2026-02-20 22:24 ` [PATCH v2 00/18] midx: incremental MIDX/bitmap layer compaction Junio C Hamano
2026-02-23 14:08 ` Jeff King
2026-02-24 5:25 ` Taylor Blau
2026-02-24 18:59 ` [PATCH v3 00/17] " Taylor Blau
2026-02-24 18:59 ` [PATCH v3 01/17] midx: mark `get_midx_checksum()` arguments as const Taylor Blau
2026-02-24 18:59 ` [PATCH v3 02/17] midx: rename `get_midx_checksum()` to `midx_get_checksum_hash()` Taylor Blau
2026-02-24 18:59 ` [PATCH v3 03/17] midx: introduce `midx_get_checksum_hex()` Taylor Blau
2026-02-24 18:59 ` [PATCH v3 04/17] builtin/multi-pack-index.c: make '--progress' a common option Taylor Blau
2026-02-24 18:59 ` [PATCH v3 05/17] git-multi-pack-index(1): remove non-existent incompatibility Taylor Blau
2026-02-24 18:59 ` [PATCH v3 06/17] git-multi-pack-index(1): align SYNOPSIS with 'git multi-pack-index -h' Taylor Blau
2026-02-24 19:00 ` [PATCH v3 07/17] t/t5319-multi-pack-index.sh: fix copy-and-paste error in t5319.39 Taylor Blau
2026-02-24 19:00 ` [PATCH v3 08/17] midx-write.c: don't use `pack_perm` when assigning `bitmap_pos` Taylor Blau
2026-02-24 19:00 ` [PATCH v3 09/17] midx-write.c: introduce `struct write_midx_opts` Taylor Blau
2026-02-24 19:00 ` [PATCH v3 10/17] midx: do not require packs to be sorted in lexicographic order Taylor Blau
2026-02-24 19:00 ` [PATCH v3 11/17] midx-write.c: introduce `midx_pack_perm()` helper Taylor Blau
2026-02-24 19:00 ` [PATCH v3 12/17] midx-write.c: extract `fill_pack_from_midx()` Taylor Blau
2026-02-24 19:00 ` [PATCH v3 13/17] midx-write.c: enumerate `pack_int_id` values directly Taylor Blau
2026-02-24 19:00 ` [PATCH v3 14/17] midx-write.c: factor fanout layering from `compute_sorted_entries()` Taylor Blau
2026-02-24 19:00 ` [PATCH v3 15/17] t/helper/test-read-midx.c: plug memory leak when selecting layer Taylor Blau
2026-02-24 19:00 ` [PATCH v3 16/17] midx: implement MIDX compaction Taylor Blau
2026-02-24 19:00 ` [PATCH v3 17/17] midx: enable reachability bitmaps during " Taylor Blau
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