Build everything as C++ (#1176)

include/helpers.hpp

@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: MIT */
+
+#ifndef HELPERS_H
+#define HELPERS_H
+
+// Ideally, we'd use `__has_attribute` and `__has_builtin`, but these were only introduced in GCC 9
+#ifdef __GNUC__ // GCC or compatible
+	#define format_(archetype, str_index, first_arg) \
+		__attribute__ ((format (archetype, str_index, first_arg)))
+	#define attr_(...) __attribute__ ((__VA_ARGS__))
+	// In release builds, define "unreachable" as such, but trap in debug builds
+	#ifdef NDEBUG
+		#define unreachable_	__builtin_unreachable
+	#else
+		#define unreachable_	__builtin_trap
+	#endif
+#else
+	// Unsupported, but no need to throw a fit
+	#define format_(archetype, str_index, first_arg)
+	#define attr_(...)
+	// This seems to generate similar code to __builtin_unreachable, despite different semantics
+	// Note that executing this is undefined behavior (declared [[noreturn]], but does return)
+	[[noreturn]] static inline void unreachable_(void) {}
+#endif
+
+// Use builtins whenever possible, and shim them otherwise
+#ifdef __GNUC__ // GCC or compatible
+	#define ctz __builtin_ctz
+	#define clz __builtin_clz
+
+#elif defined(_MSC_VER)
+	#include <assert.h>
+	#include <intrin.h>
+	#pragma intrinsic(_BitScanReverse, _BitScanForward)
+	static inline int ctz(unsigned int x)
+	{
+		unsigned long cnt;
+
+		assert(x != 0);
+		_BitScanForward(&cnt, x);
+		return cnt;
+	}
+	static inline int clz(unsigned int x)
+	{
+		unsigned long cnt;
+
+		assert(x != 0);
+		_BitScanReverse(&cnt, x);
+		return 31 - cnt;
+	}
+
+#else
+	#include <limits.h>
+	static inline int ctz(unsigned int x)
+	{
+		int cnt = 0;
+
+		while (!(x & 1)) {
+			x >>= 1;
+			cnt++;
+		}
+		return cnt;
+	}
+
+	static inline int clz(unsigned int x)
+	{
+		int cnt = 0;
+
+		while (x <= UINT_MAX / 2) {
+			x <<= 1;
+			cnt++;
+		}
+		return cnt;
+	}
+#endif
+
+// Macros for stringification
+#define STR(x) #x
+#define EXPAND_AND_STR(x) STR(x)
+
+// Obtaining the size of an array; `arr` must be an expression, not a type!
+// (Having two instances of `arr` is OK because the contents of `sizeof` are not evaluated.)
+#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof *(arr))
+
+#endif // HELPERS_H