Re: [PATCH] hex: use unsigned index for ring buffer
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Oct 25, 2016, 18:28 UTC
- Message-ID
- <xmqqd1ios2p3.fsf@gitster.mtv.corp.google.com>
- In-Reply-To
- <20161025003023.6vaqofsixana3zno@sigill.intra.peff.net>
Jeff King <peff@peff.net> writes:
Show 9 quoted lines
> On Mon, Oct 24, 2016 at 04:53:50PM -0700, Junio C Hamano wrote: > >> > So how about this? It gets rid of magic number 3 and works for array >> > size that's not a power of two. And as a nice side effect it can't >> > trigger a signed overflow anymore. >> >> Looks good to me. Peff? > > Any of the variants discussed in this thread is fine by me.
OK, here is what I'll queue then. I assumed that René wants to sign it off ;-).
-- >8 -- From: René Scharfe <l.s.r@web.de> Date: Sun, 23 Oct 2016 19:57:30 +0200 Subject: [PATCH] hex: make wraparound of the index into ring-buffer explicit
Overflow is defined for unsigned integers, but not for signed ones.
We could make the ring-buffer index in sha1_to_hex() and get_pathname() unsigned to be on the safe side to resolve this, but let's make it explicit that we are wrapping around at whatever the number of elements the ring-buffer has. The compiler is smart enough to turn modulus into bitmask for these codepaths that use ring-buffers of a size that is a power of 2.
Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com> --- hex.c | 3 ++- path.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/hex.c b/hex.c index ab2610e498..845b01a874 100644 --- a/hex.c +++ b/hex.c @@ -78,7 +78,8 @@ char *sha1_to_hex(const unsigned char *sha1) { static int bufno; static char hexbuffer[4][GIT_SHA1_HEXSZ + 1]; - return sha1_to_hex_r(hexbuffer[3 & ++bufno], sha1); + bufno = (bufno + 1) % ARRAY_SIZE(hexbuffer); + return sha1_to_hex_r(hexbuffer[bufno], sha1); } char *oid_to_hex(const struct object_id *oid) diff --git a/path.c b/path.c index fe3c4d96c6..9bfaeda207 100644 --- a/path.c +++ b/path.c @@ -24,7 +24,8 @@ static struct strbuf *get_pathname(void) STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT }; static int index; - struct strbuf *sb = &pathname_array[3 & ++index]; + struct strbuf *sb = &pathname_array[index]; + index = (index + 1) % ARRAY_SIZE(pathname_array); strbuf_reset(sb); return sb; }
-- 2.10.1-777-gd068e6bde7