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[31.211.229.121]) by smtp.gmail.com with ESMTPSA id c19sm32835lfg.86.2018.10.28.08.32.11 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Oct 2018 08:32:12 -0700 (PDT) From: =?utf-8?q?Martin_=C3=85gren?= To: git@vger.kernel.org Cc: Johannes Schindelin Subject: [PATCH] sequencer: clarify intention to break out of loop Date: Sun, 28 Oct 2018 16:31:45 +0100 Message-Id: <20181028153145.25734-1-martin.agren@gmail.com> X-Mailer: git-send-email 2.19.1.593.gc670b1f876.dirty MIME-Version: 1.0 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When we find a space, we set `len = i`, which gives us the answer we are looking for, but which also breaks out of the loop through these steps: 1. `len = i` 2. `i = i + 1` 3. Is `i < len`? No, so break out. Since `i` is signed, step 2 is undefined if `i` has the value `INT_MAX`. It can't actually have that value, but that doesn't stop my copy of gcc 7.3.0 from throwing the following: > sequencer.c:2853:3: error: assuming signed overflow does not occur when > assuming that (X + c) < X is always false [-Werror=strict-overflow] > for (i = 0; i < len; i++) > ^~~ That is, the compiler has realized that the code is essentially evaluating "(len + 1) < len" and that for `len = INT_MAX`, this is undefined behavior. What it hasn't figured out is that if `i` and `len` are both `INT_MAX` after step 1, then `len` must have had a value larger than `INT_MAX` before that step, which it can't have had. Let's be explicit about breaking out of the loop. This helps the compiler grok our intention. As a bonus, it might make it (even) more obvious to human readers that the loop stops at the first space. While at it, reduce the scope of `i`. Signed-off-by: Martin Ågren --- sequencer.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/sequencer.c b/sequencer.c index 0c164d5f98..a351638ad9 100644 --- a/sequencer.c +++ b/sequencer.c @@ -2829,7 +2829,7 @@ static int do_reset(const char *name, int len, struct replay_opts *opts) struct tree_desc desc; struct tree *tree; struct unpack_trees_options unpack_tree_opts; - int ret = 0, i; + int ret = 0; if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0) return -1; @@ -2849,10 +2849,14 @@ static int do_reset(const char *name, int len, struct replay_opts *opts) } oidcpy(&oid, &opts->squash_onto); } else { + int i; /* Determine the length of the label */ - for (i = 0; i < len; i++) - if (isspace(name[i])) + for (i = 0; i < len; i++) { + if (isspace(name[i])) { len = i; + break; + } + } strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name); if (get_oid(ref_name.buf, &oid) &&