Re: [PATCH 3/3] wrapper: use a loop instead of repetitive statements

From: Jeff King <peff@peff.net>
Date: Sep 27, 2019, 02:45 UTC
Message-ID: <20190927024502.GC23736@sigill.intra.peff.net>
In-Reply-To: <20190925020158.751492-4-alexhenrie24@gmail.com>

On Tue, Sep 24, 2019 at 08:01:58PM -0600, Alex Henrie wrote:

Show 20 quoted lines

> diff --git a/wrapper.c b/wrapper.c
> index c55d7722d7..c23ac6adcd 100644
> --- a/wrapper.c
> +++ b/wrapper.c
> @@ -469,13 +469,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
>  	filename_template = &pattern[len - 6 - suffix_len];
>  	for (count = 0; count < TMP_MAX; ++count) {
>  		uint64_t v = value;
> +		int i;
>  		/* Fill in the random bits. */
> -		filename_template[0] = letters[v % num_letters]; v /= num_letters;
> -		filename_template[1] = letters[v % num_letters]; v /= num_letters;
> -		filename_template[2] = letters[v % num_letters]; v /= num_letters;
> -		filename_template[3] = letters[v % num_letters]; v /= num_letters;
> -		filename_template[4] = letters[v % num_letters]; v /= num_letters;
> -		filename_template[5] = letters[v % num_letters]; v /= num_letters;
> +		for (i = 0; i < 6; i++) {
> +			filename_template[i] = letters[v % num_letters];
> +			v /= num_letters;
> +		}

I'm not sure the readability is changed much either way. But it does enable this additional cleanup on top:

-- >8 --
Subject: git_mkstemps_mode(): replace magic numbers with computed value

The magic number "6" appears several times in the function, and is related to the size of the "XXXXXX" string we expect to find in the template. Let's pull that "XXXXXX" into a constant array, whose size we can get at compile time with ARRAY_SIZE().

Note that we probably can't just change this value, since callers will be feeding us a certain number of X's, but it hopefully makes the function itself easier to follow.

While we're here, let's do the same with the "letters" array (which we _could_ modify if we wanted to include more characters).

Signed-off-by: Jeff King <peff@peff.net>
---
 wrapper.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/wrapper.c b/wrapper.c
index c23ac6adcd..e1eaef2e16 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -441,7 +441,9 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 		"abcdefghijklmnopqrstuvwxyz"
 		"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 		"0123456789";
-	static const int num_letters = 62;
+	static const int num_letters = ARRAY_SIZE(letters) - 1;
+	static const char x_pattern[] = "XXXXXX";
+	static const int num_x = ARRAY_SIZE(x_pattern) - 1;
 	uint64_t value;
 	struct timeval tv;
 	char *filename_template;
@@ -450,12 +452,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 
 	len = strlen(pattern);
 
-	if (len < 6 + suffix_len) {
+	if (len < num_x + suffix_len) {
 		errno = EINVAL;
 		return -1;
 	}
 
-	if (strncmp(&pattern[len - 6 - suffix_len], "XXXXXX", 6)) {
+	if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) {
 		errno = EINVAL;
 		return -1;
 	}
@@ -466,12 +468,12 @@ int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 	 */
 	gettimeofday(&tv, NULL);
 	value = ((uint64_t)tv.tv_usec << 16) ^ tv.tv_sec ^ getpid();
-	filename_template = &pattern[len - 6 - suffix_len];
+	filename_template = &pattern[len - num_x - suffix_len];
 	for (count = 0; count < TMP_MAX; ++count) {
 		uint64_t v = value;
 		int i;
 		/* Fill in the random bits. */
-		for (i = 0; i < 6; i++) {
+		for (i = 0; i < num_x; i++) {
 			filename_template[i] = letters[v % num_letters];
 			v /= num_letters;
 		}

-- 
2.23.0.765.g1fc3e247e7