Re: [PATCH 1/3] compat: add qsort_s()

["René Scharfe" <l.s.r@web.de>]

Am 01.12.2016 um 17:26 schrieb René Scharfe:
> The function qsort_s() was introduced with C11 Annex K; it provides the
> ability to pass a context pointer to the comparison function, supports
> the convention of using a NULL pointer for an empty array and performs a
> few safety checks.
> 
> Add an implementation based on compat/qsort.c for platforms that lack a
> native standards-compliant qsort_s() (i.e. basically everyone).  It
> doesn't perform the full range of possible checks: It uses size_t
> instead of rsize_t and doesn't check nmemb and size against RSIZE_MAX
> because we probably don't have the restricted size type defined.  For
> the same reason it returns int instead of errno_t.
> 
> Signed-off-by: Rene Scharfe <l.s.r@web.de>
> ---
>  Makefile          | 10 ++++++++
>  compat/qsort_s.c  | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  git-compat-util.h |  6 +++++
>  3 files changed, 85 insertions(+)
>  create mode 100644 compat/qsort_s.c

And here's the diff for compat/qsort_s.c with copy detection (-C -C):
---
 compat/{qsort.c => qsort_s.c} | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/compat/qsort.c b/compat/qsort_s.c
similarity index 62%
copy from compat/qsort.c
copy to compat/qsort_s.c
index 7d071afb7..52d1f0a73 100644
--- a/compat/qsort.c
+++ b/compat/qsort_s.c
@@ -3,11 +3,12 @@
 /*
  * A merge sort implementation, simplified from the qsort implementation
  * by Mike Haertel, which is a part of the GNU C Library.
+ * Added context pointer, safety checks and return value.
  */
 
 static void msort_with_tmp(void *b, size_t n, size_t s,
-			   int (*cmp)(const void *, const void *),
-			   char *t)
+			   int (*cmp)(const void *, const void *, void *),
+			   char *t, void *ctx)
 {
 	char *tmp;
 	char *b1, *b2;
@@ -21,13 +22,13 @@ static void msort_with_tmp(void *b, size_t n, size_t s,
 	b1 = b;
 	b2 = (char *)b + (n1 * s);
 
-	msort_with_tmp(b1, n1, s, cmp, t);
-	msort_with_tmp(b2, n2, s, cmp, t);
+	msort_with_tmp(b1, n1, s, cmp, t, ctx);
+	msort_with_tmp(b2, n2, s, cmp, t, ctx);
 
 	tmp = t;
 
 	while (n1 > 0 && n2 > 0) {
-		if (cmp(b1, b2) <= 0) {
+		if (cmp(b1, b2, ctx) <= 0) {
 			memcpy(tmp, b1, s);
 			tmp += s;
 			b1 += s;
@@ -44,19 +45,25 @@ static void msort_with_tmp(void *b, size_t n, size_t s,
 	memcpy(b, t, (n - n2) * s);
 }
 
-void git_qsort(void *b, size_t n, size_t s,
-	       int (*cmp)(const void *, const void *))
+int git_qsort_s(void *b, size_t n, size_t s,
+		int (*cmp)(const void *, const void *, void *), void *ctx)
 {
 	const size_t size = st_mult(n, s);
 	char buf[1024];
 
+	if (!n)
+		return 0;
+	if (!b || !cmp)
+		return -1;
+
 	if (size < sizeof(buf)) {
 		/* The temporary array fits on the small on-stack buffer. */
-		msort_with_tmp(b, n, s, cmp, buf);
+		msort_with_tmp(b, n, s, cmp, buf, ctx);
 	} else {
 		/* It's somewhat large, so malloc it.  */
 		char *tmp = xmalloc(size);
-		msort_with_tmp(b, n, s, cmp, tmp);
+		msort_with_tmp(b, n, s, cmp, tmp, ctx);
 		free(tmp);
 	}
+	return 0;
 }