Add VLA compatibility macro for C89-ish compilers.

1 files changed, 43 insertions, 0 deletions

diff --git a/toxcore/ccompat.h b/toxcore/ccompat.h
new file mode 100644
index 00000000..e72e66ae
--- /dev/null
+++ b/toxcore/ccompat.h
@@ -0,0 +1,43 @@
+/*
+ * C language compatibility macros for varying compiler support.
+ */
+#ifndef CCOMPAT_H
+#define CCOMPAT_H
+
+// Marking GNU extensions to avoid warnings.
+#if defined(__GNUC__)
+#define GNU_EXTENSION __extension__
+#else
+#define GNU_EXTENSION
+#endif
+
+// Variable length arrays.
+// VLA(type, name, size) allocates a variable length array with automatic
+// storage duration. VLA_SIZE(name) evaluates to the runtime size of that array
+// in bytes.
+//
+// If C99 VLAs are not available, an emulation using alloca (stack allocation
+// "function") is used. Note the semantic difference: alloca'd memory does not
+// get freed at the end of the declaration's scope. Do not use VLA() in loops or
+// you may run out of stack space.
+#if !defined(_MSC_VER) && __STDC_VERSION__ >= 199901L
+// C99 VLAs.
+#define VLA(type, name, size) type name[size]
+#define SIZEOF_VLA sizeof
+#else
+
+// Emulation using alloca.
+#ifdef _WIN32
+#include <malloc.h>
+#else
+#include <alloca.h>
+#endif
+
+#define VLA(type, name, size)                           \
+  const size_t name##_size = (size) * sizeof(type);     \
+  type *const name = (type *)alloca(name##_size)
+#define SIZEOF_VLA(name) name##_size
+
+#endif
+
+#endif /* CCOMPAT_H */