1 files changed, 50 insertions, 0 deletions
diff --git a/compat/bswap.h b/compat/bswap.h
new file mode 100644
index 0000000000..5061214f73
--- /dev/null
+++ b/compat/bswap.h
@@ -0,0 +1,50 @@
+/*
+ * Let's make sure we always have a sane definition for ntohl()/htonl().
+ * Some libraries define those as a function call, just to perform byte
+ * shifting, bringing significant overhead to what should be a simple
+ * operation.
+ */
+
+/*
+ * Default version that the compiler ought to optimize properly with
+ * constant values.
+ */
+static inline uint32_t default_swab32(uint32_t val)
+{
+	return (((val & 0xff000000) >> 24) |
+		((val & 0x00ff0000) >>  8) |
+		((val & 0x0000ff00) <<  8) |
+		((val & 0x000000ff) << 24));
+}
+
+#undef bswap32
+
+#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
+
+#define bswap32 git_bswap32
+static inline uint32_t git_bswap32(uint32_t x)
+{
+	uint32_t result;
+	if (__builtin_constant_p(x))
+		result = default_swab32(x);
+	else
+		__asm__("bswap %0" : "=r" (result) : "0" (x));
+	return result;
+}
+
+#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
+
+#include <stdlib.h>
+
+#define bswap32(x) _byteswap_ulong(x)
+
+#endif
+
+#ifdef bswap32
+
+#undef ntohl
+#undef htonl
+#define ntohl(x) bswap32(x)
+#define htonl(x) bswap32(x)
+
+#endif