From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: "Derrick Stolee" <stolee@gmail.com>,
"SZEDER Gábor" <szeder.dev@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Stefan Beller" <sbeller@google.com>, git <git@vger.kernel.org>,
"Duy Nguyen" <pclouds@gmail.com>
Subject: Re: [PoC -- do not apply 3/3] test-tree-bitmap: replace ewah with custom rle encoding
Date: Wed, 10 Oct 2018 09:58:51 +0900 [thread overview]
Message-ID: <xmqqr2gyobw4.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20181009231441.GC23730@sigill.intra.peff.net> (Jeff King's message of "Tue, 9 Oct 2018 19:14:41 -0400")
Jeff King <peff@peff.net> writes:
> +static void strbuf_add_varint(struct strbuf *out, uintmax_t val)
> +{
> + size_t len;
> + strbuf_grow(out, 16); /* enough for any varint */
> + len = encode_varint(val, (unsigned char *)out->buf + out->len);
> + strbuf_setlen(out, out->len + len);
> +}
> +
> +static void bitmap_to_rle(struct strbuf *out, struct bitmap *bitmap)
> +{
> + int curval = 0; /* count zeroes, then ones, then zeroes, etc */
> + size_t run = 0;
> + size_t word;
> + size_t orig_len = out->len;
> +
> + for (word = 0; word < bitmap->word_alloc; word++) {
> + int bit;
> +
> + for (bit = 0; bit < BITS_IN_EWORD; bit++) {
> + int val = !!(bitmap->words[word] & (((eword_t)1) << bit));
> + if (val == curval)
> + run++;
> + else {
> + strbuf_add_varint(out, run);
> + curval = 1 - curval; /* flip 0/1 */
> + run = 1;
> + }
> + }
OK. I find it a bit disturbing to see that the loop knows a bit too
much about how "struct bitmap" is implemented, but that is a complaint
against the bitmap API, not this new user of the API.
We do not try to handle the case where bitmap has bits that is not
multiple of BITS_IN_EWORD and instead pretend that size of such a
bitmap can be rounded up, because we ignore trailing 0-bit anyway,
and we know the "struct bitmap" would pad with 0-bit at the tail?
> + }
> +
> + /*
> + * complete the run, but do not bother with trailing zeroes, unless we
> + * failed to write even an initial run of 0's.
> + */
> + if (curval && run)
> + strbuf_add_varint(out, run);
> + else if (orig_len == out->len)
> + strbuf_add_varint(out, 0);
> +
> + /* signal end-of-input with an empty run */
> + strbuf_add_varint(out, 0);
> +}
OK.
> +static size_t rle_each_bit(const unsigned char *in, size_t len,
> + void (*fn)(size_t, void *), void *data)
> +{
> + int curval = 0; /* look for zeroes first, then ones, etc */
> + const unsigned char *cur = in;
> + const unsigned char *end = in + len;
> + size_t pos;
> +
> + /* we always have a first run, even if it's 0 zeroes */
> + pos = decode_varint(&cur);
> +
> + /*
> + * ugh, varint does not seem to have a way to prevent reading past
> + * the end of the buffer. We'll do a length check after each one,
> + * so the worst case is bounded.
> + */
Sorry about that :-).
> + if (cur > end) {
> + error("input underflow in rle");
> + return len;
> + }
> +
> + while (1) {
> + size_t run = decode_varint(&cur);
> +
> + if (cur > end) {
> + error("input underflow in rle");
> + return len;
> + }
> +
> + if (!run)
> + break; /* empty run signals end */
> +
> + curval = 1 - curval; /* flip 0/1 */
> + if (curval) {
> + /* we have a run of 1's; deliver them */
> + size_t i;
> + for (i = 0; i < run; i++)
> + fn(pos + i, data);
> + }
> + pos += run;
> + }
> +
> + return cur - in;
> +}
Makes sense.
next prev parent reply other threads:[~2018-10-10 0:58 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-03 13:23 We should add a "git gc --auto" after "git clone" due to commit graph Ævar Arnfjörð Bjarmason
2018-10-03 13:36 ` SZEDER Gábor
2018-10-03 13:42 ` Derrick Stolee
2018-10-03 14:18 ` Ævar Arnfjörð Bjarmason
2018-10-03 14:01 ` Ævar Arnfjörð Bjarmason
2018-10-03 14:17 ` SZEDER Gábor
2018-10-03 14:22 ` Ævar Arnfjörð Bjarmason
2018-10-03 14:53 ` SZEDER Gábor
2018-10-03 15:19 ` Ævar Arnfjörð Bjarmason
2018-10-03 16:59 ` SZEDER Gábor
2018-10-05 6:09 ` Junio C Hamano
2018-10-10 22:07 ` SZEDER Gábor
2018-10-10 23:01 ` Ævar Arnfjörð Bjarmason
2018-10-03 19:08 ` Stefan Beller
2018-10-03 19:21 ` Jeff King
2018-10-03 20:35 ` Ævar Arnfjörð Bjarmason
2018-10-03 17:47 ` Stefan Beller
2018-10-03 18:47 ` Ævar Arnfjörð Bjarmason
2018-10-03 18:51 ` Jeff King
2018-10-03 18:59 ` Derrick Stolee
2018-10-03 19:18 ` Jeff King
2018-10-08 16:41 ` SZEDER Gábor
2018-10-08 16:57 ` Derrick Stolee
2018-10-08 18:10 ` SZEDER Gábor
2018-10-08 18:29 ` Derrick Stolee
2018-10-09 3:08 ` Jeff King
2018-10-09 13:48 ` Bloom Filters (was Re: We should add a "git gc --auto" after "git clone" due to commit graph) Derrick Stolee
2018-10-09 18:45 ` Ævar Arnfjörð Bjarmason
2018-10-09 18:46 ` Jeff King
2018-10-09 19:03 ` Derrick Stolee
2018-10-09 21:14 ` Jeff King
2018-10-09 23:12 ` Bloom Filters Jeff King
2018-10-09 23:13 ` [PoC -- do not apply 1/3] initial tree-bitmap proof of concept Jeff King
2018-10-09 23:14 ` [PoC -- do not apply 2/3] test-tree-bitmap: add "dump" mode Jeff King
2018-10-10 0:48 ` Junio C Hamano
2018-10-11 3:13 ` Jeff King
2018-10-09 23:14 ` [PoC -- do not apply 3/3] test-tree-bitmap: replace ewah with custom rle encoding Jeff King
2018-10-10 0:58 ` Junio C Hamano [this message]
2018-10-11 3:20 ` Jeff King
2018-10-11 12:33 ` Bloom Filters Derrick Stolee
2018-10-11 13:43 ` Jeff King
2018-10-09 21:30 ` We should add a "git gc --auto" after "git clone" due to commit graph SZEDER Gábor
2018-10-09 19:34 ` [PATCH 0/4] Bloom filter experiment SZEDER Gábor
2018-10-09 19:34 ` [PATCH 1/4] Add a (very) barebones Bloom filter implementation SZEDER Gábor
2018-10-09 19:34 ` [PATCH 2/4] commit-graph: write a Bloom filter containing changed paths for each commit SZEDER Gábor
2018-10-09 21:06 ` Jeff King
2018-10-09 21:37 ` SZEDER Gábor
2018-10-09 19:34 ` [PATCH 3/4] revision.c: use the Bloom filter to speed up path-limited revision walks SZEDER Gábor
2018-10-09 19:34 ` [PATCH 4/4] revision.c: add GIT_TRACE_BLOOM_FILTER for a bit of statistics SZEDER Gábor
2018-10-09 19:47 ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-11 1:21 ` [PATCH 0/2] Per-commit filter proof of concept Jonathan Tan
2018-10-11 1:21 ` [PATCH 1/2] One filter per commit Jonathan Tan
2018-10-11 12:49 ` Derrick Stolee
2018-10-11 19:11 ` [PATCH] Per-commit and per-parent filters for 2 parents Jonathan Tan
2018-10-11 1:21 ` [PATCH 2/2] Only make bloom filter for first parent Jonathan Tan
2018-10-11 7:37 ` [PATCH 0/2] Per-commit filter proof of concept Ævar Arnfjörð Bjarmason
2018-10-15 14:39 ` [PATCH 0/4] Bloom filter experiment Derrick Stolee
2018-10-16 4:45 ` Junio C Hamano
2018-10-16 11:13 ` Derrick Stolee
2018-10-16 12:57 ` Ævar Arnfjörð Bjarmason
2018-10-16 13:03 ` Derrick Stolee
2018-10-18 2:00 ` Junio C Hamano
2018-10-16 23:41 ` Jonathan Tan
2018-10-08 23:02 ` We should add a "git gc --auto" after "git clone" due to commit graph Junio C Hamano
2018-10-03 14:32 ` Duy Nguyen
2018-10-03 16:45 ` Duy Nguyen
2018-10-04 21:42 ` [RFC PATCH] " Ævar Arnfjörð Bjarmason
2018-10-05 12:05 ` Derrick Stolee
2018-10-05 13:05 ` Ævar Arnfjörð Bjarmason
2018-10-05 13:45 ` Derrick Stolee
2018-10-05 14:04 ` Ævar Arnfjörð Bjarmason
2018-10-05 19:21 ` Jeff King
2018-10-05 19:41 ` Derrick Stolee
2018-10-05 19:47 ` Jeff King
2018-10-05 20:00 ` Derrick Stolee
2018-10-05 20:02 ` Jeff King
2018-10-05 20:01 ` Ævar Arnfjörð Bjarmason
2018-10-05 20:09 ` Jeff King
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