1 files changed, 56 insertions, 0 deletions
diff --git a/portable/reallocarray.c b/portable/reallocarray.c
new file mode 100644
index 0000000..e9404e9
--- /dev/null
+++ b/portable/reallocarray.c
@@ -0,0 +1,56 @@
+/*
+ * Replacement for a missing reallocarray.
+ *
+ * Provides the same functionality as the OpenBSD library function
+ * reallocarray for those systems that don't have it.  This function is the
+ * same as realloc, but takes the size arguments in the same form as calloc
+ * and checks for overflow so that the caller doesn't need to.
+ *
+ * The canonical version of this file is maintained in the rra-c-util package,
+ * which can be found at <http://www.eyrie.org/~eagle/software/rra-c-util/>.
+ *
+ * Written by Russ Allbery <eagle@eyrie.org>
+ *
+ * The authors hereby relinquish any claim to any copyright that they may have
+ * in this work, whether granted under contract or by operation of law or
+ * international treaty, and hereby commit to the public, at large, that they
+ * shall not, at any time in the future, seek to enforce any copyright in this
+ * work against any person or entity, or prevent any person or entity from
+ * copying, publishing, distributing or creating derivative works of this
+ * work.
+ */
+
+#include <config.h>
+#include <portable/system.h>
+
+#include <errno.h>
+
+/*
+ * If we're running the test suite, rename reallocarray to avoid conflicts
+ * with the system version.  #undef it first because some systems may define
+ * it to another name.
+ */
+#if TESTING
+# undef reallocarray
+# define reallocarray test_reallocarray
+void *test_reallocarray(void *, size_t, size_t);
+#endif
+
+/*
+ * nmemb * size cannot overflow if both are smaller than sqrt(SIZE_MAX).  We
+ * can calculate that value statically by using 2^(sizeof(size_t) * 8) as the
+ * value of SIZE_MAX and then taking the square root, which gives
+ * 2^(sizeof(size_t) * 4).  Compute the exponentiation with shift.
+ */
+#define CHECK_THRESHOLD (1UL << (sizeof(size_t) * 4))
+
+void *
+reallocarray(void *ptr, size_t nmemb, size_t size)
+{
+    if (nmemb >= CHECK_THRESHOLD || size >= CHECK_THRESHOLD)
+        if (nmemb > 0 && SIZE_MAX / nmemb <= size) {
+            errno = ENOMEM;
+            return NULL;
+        }
+    return realloc(ptr, nmemb * size);
+}