util: do not perform allocations in insertsort

Our hand-rolled fallback sorting function `git__insertsort_r` does an
in-place sort of the given array. As elements may not necessarily be
pointers, it needs a way of swapping two values of arbitrary size, which
is currently implemented by allocating a temporary buffer of the
element's size. This is problematic, though, as the emulated `qsort`
interface doesn't provide any return values and thus cannot signal an
error if allocation of that temporary buffer has failed.

Convert the function to swap via a temporary buffer allocated on the
stack. Like this, it can `memcpy` contents of both elements in small
batches without requiring a heap allocation. The buffer size has been
chosen such that in most cases, a single iteration of copying will
suffice. Most importantly, it can fully contain `git_oid` structures and
pointers.

Add a bunch of tests for the `git__qsort_r` interface to verify nothing
breaks. Furthermore, this removes the declaration of `git__insertsort_r`
and makes it static as it is not used anywhere else.

1 files changed, 90 insertions, 0 deletions

diff --git a/tests/core/qsort.c b/tests/core/qsort.c
new file mode 100644
index 000000000..efb79e6e9
--- /dev/null
+++ b/tests/core/qsort.c
@@ -0,0 +1,90 @@
+#include "clar_libgit2.h"
+
+#define assert_sorted(a, cmp) \
+	_assert_sorted(a, ARRAY_SIZE(a), sizeof(*a), cmp)
+
+struct big_entries {
+	char c[311];
+};
+
+static void _assert_sorted(void *els, size_t n, size_t elsize, git__sort_r_cmp cmp)
+{
+	int8_t *p = els;
+
+	git__qsort_r(p, n, elsize, cmp, NULL);
+	while (n-- > 1) {
+		cl_assert(cmp(p, p + elsize, NULL) <= 0);
+		p += elsize;
+	}
+}
+
+static int cmp_big(const void *_a, const void *_b, void *payload)
+{
+	const struct big_entries *a = (const struct big_entries *)_a, *b = (const struct big_entries *)_b;
+	GIT_UNUSED(payload);
+	return (a->c[0] < b->c[0]) ? -1 : (a->c[0] > b->c[0]) ? +1 : 0;
+}
+
+static int cmp_int(const void *_a, const void *_b, void *payload)
+{
+	int a = *(const int *)_a, b = *(const int *)_b;
+	GIT_UNUSED(payload);
+	return (a < b) ? -1 : (a > b) ? +1 : 0;
+}
+
+static int cmp_str(const void *_a, const void *_b, void *payload)
+{
+	GIT_UNUSED(payload);
+	return strcmp((const char *) _a, (const char *) _b);
+}
+
+void test_core_qsort__array_with_single_entry(void)
+{
+	int a[] = { 10 };
+	assert_sorted(a, cmp_int);
+}
+
+void test_core_qsort__array_with_equal_entries(void)
+{
+	int a[] = { 4, 4, 4, 4 };
+	assert_sorted(a, cmp_int);
+}
+
+void test_core_qsort__sorted_array(void)
+{
+	int a[] = { 1, 10 };
+	assert_sorted(a, cmp_int);
+}
+
+void test_core_qsort__unsorted_array(void)
+{
+	int a[] = { 123, 9, 412938, 10, 234, 89 };
+	assert_sorted(a, cmp_int);
+}
+
+void test_core_qsort__sorting_strings(void)
+{
+	char *a[] = { "foo", "bar", "baz" };
+	assert_sorted(a, cmp_str);
+}
+
+void test_core_qsort__sorting_big_entries(void)
+{
+	struct big_entries a[5];
+
+	memset(&a, 0, sizeof(a));
+
+	memset(a[0].c, 'w', sizeof(a[0].c) - 1);
+	memset(a[1].c, 'c', sizeof(a[1].c) - 1);
+	memset(a[2].c, 'w', sizeof(a[2].c) - 1);
+	memset(a[3].c, 'h', sizeof(a[3].c) - 1);
+	memset(a[4].c, 'a', sizeof(a[4].c) - 1);
+
+	assert_sorted(a, cmp_big);
+
+	cl_assert_equal_i(strspn(a[0].c, "a"), sizeof(a[0].c) - 1);
+	cl_assert_equal_i(strspn(a[1].c, "c"), sizeof(a[1].c) - 1);
+	cl_assert_equal_i(strspn(a[2].c, "h"), sizeof(a[2].c) - 1);
+	cl_assert_equal_i(strspn(a[3].c, "w"), sizeof(a[3].c) - 1);
+	cl_assert_equal_i(strspn(a[4].c, "w"), sizeof(a[4].c) - 1);
+}