Fix a POSIX violation for swab

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/test_swab_negative.c b/tests/test_swab_negative.c
new file mode 100644
index 0000000..f9c182b
--- /dev/null
+++ b/tests/test_swab_negative.c
@@ -0,0 +1,19 @@
+#include "common.h"
+
+#include <unistd.h>
+
+int main(int argc, char** argv) {
+  char src[8] = "ABCDEFG";
+  char dst[8] = {0};
+
+  /* Positive case: normal swab works */
+  swab(src, dst, 6);
+  puts(dst);
+
+  /* Negative n: POSIX says swab does nothing, must NOT trap */
+  swab(src, dst, -1);
+  swab(src, dst, -100);
+
+  puts(dst);
+  return ret;
+}