merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 62 insertions, 0 deletions

diff --git a/third_party/git/stable-qsort.c b/third_party/git/stable-qsort.c
new file mode 100644
index 0000000000..6cbaf39f7b
--- /dev/null
+++ b/third_party/git/stable-qsort.c
@@ -0,0 +1,62 @@
+#include "git-compat-util.h"
+
+/*
+ * A merge sort implementation, simplified from the qsort implementation
+ * by Mike Haertel, which is a part of the GNU C Library.
+ */
+
+static void msort_with_tmp(void *b, size_t n, size_t s,
+			   int (*cmp)(const void *, const void *),
+			   char *t)
+{
+	char *tmp;
+	char *b1, *b2;
+	size_t n1, n2;
+
+	if (n <= 1)
+		return;
+
+	n1 = n / 2;
+	n2 = n - n1;
+	b1 = b;
+	b2 = (char *)b + (n1 * s);
+
+	msort_with_tmp(b1, n1, s, cmp, t);
+	msort_with_tmp(b2, n2, s, cmp, t);
+
+	tmp = t;
+
+	while (n1 > 0 && n2 > 0) {
+		if (cmp(b1, b2) <= 0) {
+			memcpy(tmp, b1, s);
+			tmp += s;
+			b1 += s;
+			--n1;
+		} else {
+			memcpy(tmp, b2, s);
+			tmp += s;
+			b2 += s;
+			--n2;
+		}
+	}
+	if (n1 > 0)
+		memcpy(tmp, b1, n1 * s);
+	memcpy(b, t, (n - n2) * s);
+}
+
+void git_stable_qsort(void *b, size_t n, size_t s,
+		      int (*cmp)(const void *, const void *))
+{
+	const size_t size = st_mult(n, s);
+	char buf[1024];
+
+	if (size < sizeof(buf)) {
+		/* The temporary array fits on the small on-stack buffer. */
+		msort_with_tmp(b, n, s, cmp, buf);
+	} else {
+		/* It's somewhat large, so malloc it.  */
+		char *tmp = xmalloc(size);
+		msort_with_tmp(b, n, s, cmp, tmp);
+		free(tmp);
+	}
+}