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fill_sha1_file: write into a strbuf

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It's currently the responsibility of the caller to give
fill_sha1_file() enough bytes to write into, leading them to
manually compute the required lengths. Instead, let's just
write into a strbuf so that it's impossible to get this
wrong.

The alt_odb caller already has a strbuf, so this makes
things strictly simpler. The other caller, sha1_file_name(),
uses a static PATH_MAX buffer and dies when it would
overflow. We can convert this to a static strbuf, which
means our allocation cost is amortized (and as a bonus, we
no longer have to worry about PATH_MAX being too short for
normal use).

This does introduce some small overhead in fill_sha1_file(),
as each strbuf_addchar() will check whether it needs to
grow. However, between the optimization in fec501d
(strbuf_addch: avoid calling strbuf_grow, 2015-04-16) and
the fact that this is not generally called in a tight loop
(after all, the next step is typically to access the file!)
this probably doesn't matter. And even if it did, the right
place to micro-optimize is inside fill_sha1_file(), by
calling a single strbuf_grow() there.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2016-10-03 16:36:09 -04:00 committed by Junio C Hamano
parent 38dbe5f078
commit f7b7774f34
1 changed files with 10 additions and 24 deletions
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34
sha1_file.c
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@ -172,36 +172,28 @@ enum scld_error safe_create_leading_directories_const(const char *path)
return result;
}
static void fill_sha1_path(char *pathbuf, const unsigned char *sha1)
static void fill_sha1_path(struct strbuf *buf, const unsigned char *sha1)
{
int i;
for (i = 0; i < 20; i++) {
static char hex[] = "0123456789abcdef";
unsigned int val = sha1[i];
*pathbuf++ = hex[val >> 4];
*pathbuf++ = hex[val & 0xf];
strbuf_addch(buf, hex[val >> 4]);
strbuf_addch(buf, hex[val & 0xf]);
if (!i)
*pathbuf++ = '/';
strbuf_addch(buf, '/');
}
*pathbuf = '\0';
}
const char *sha1_file_name(const unsigned char *sha1)
{
static char buf[PATH_MAX];
const char *objdir;
int len;
static struct strbuf buf = STRBUF_INIT;
objdir = get_object_directory();
len = strlen(objdir);
strbuf_reset(&buf);
strbuf_addf(&buf, "%s/", get_object_directory());
/* '/' + sha1(2) + '/' + sha1(38) + '\0' */
if (len + 43 > PATH_MAX)
die("insanely long object directory %s", objdir);
memcpy(buf, objdir, len);
buf[len] = '/';
fill_sha1_path(buf + len + 1, sha1);
return buf;
fill_sha1_path(&buf, sha1);
return buf.buf;
}
struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
@ -213,14 +205,8 @@ struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
static const char *alt_sha1_path(struct alternate_object_database *alt,
const unsigned char *sha1)
{
/* hex sha1 plus internal "/" */
size_t len = GIT_SHA1_HEXSZ + 1;
struct strbuf *buf = alt_scratch_buf(alt);
strbuf_grow(buf, len);
fill_sha1_path(buf->buf + buf->len, sha1);
strbuf_setlen(buf, buf->len + len);
fill_sha1_path(buf, sha1);
return buf->buf;
}