[PATCH 1/3] build_assert: add ccan build_assert.h header

[David Disseldorp <ddiss@suse.de>]

Obtained from https://github.com/rustyrussell/ccan with HEAD
050dc66dc2de3d8b150817c6bba648f74b12cccf .
build_assert.h is licensed CC0 (Public domain).

Signed-off-by: David Disseldorp <ddiss@suse.de>
---
 build_assert.h | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 build_assert.h

diff --git a/build_assert.h b/build_assert.h
new file mode 100644
index 0000000..b9ecd84
--- /dev/null
+++ b/build_assert.h
@@ -0,0 +1,40 @@
+/* CC0 (Public domain) - see LICENSE file for details */
+#ifndef CCAN_BUILD_ASSERT_H
+#define CCAN_BUILD_ASSERT_H
+
+/**
+ * BUILD_ASSERT - assert a build-time dependency.
+ * @cond: the compile-time condition which must be true.
+ *
+ * Your compile will fail if the condition isn't true, or can't be evaluated
+ * by the compiler.  This can only be used within a function.
+ *
+ * Example:
+ *	#include <stddef.h>
+ *	...
+ *	static char *foo_to_char(struct foo *foo)
+ *	{
+ *		// This code needs string to be at start of foo.
+ *		BUILD_ASSERT(offsetof(struct foo, string) == 0);
+ *		return (char *)foo;
+ *	}
+ */
+#define BUILD_ASSERT(cond) \
+	do { (void) sizeof(char [1 - 2*!(cond)]); } while(0)
+
+/**
+ * BUILD_ASSERT_OR_ZERO - assert a build-time dependency, as an expression.
+ * @cond: the compile-time condition which must be true.
+ *
+ * Your compile will fail if the condition isn't true, or can't be evaluated
+ * by the compiler.  This can be used in an expression: its value is "0".
+ *
+ * Example:
+ *	#define foo_to_char(foo)					\
+ *		 ((char *)(foo)						\
+ *		  + BUILD_ASSERT_OR_ZERO(offsetof(struct foo, string) == 0))
+ */
+#define BUILD_ASSERT_OR_ZERO(cond) \
+	(sizeof(char [1 - 2*!(cond)]) - 1)
+
+#endif /* CCAN_BUILD_ASSERT_H */
-- 
2.51.0