Use optimized byte swap operations for Microsoft and GNU [Snyder].

1 files changed, 13 insertions, 0 deletions

diff --git a/zutil.h b/zutil.h
index dff1112..2f4d14d 100644
--- a/zutil.h
+++ b/zutil.h
@@ -245,4 +245,17 @@ extern const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 #define ZFREE(strm, addr)  (*((strm)->zfree))((strm)->opaque, (voidpf)(addr))
 #define TRY_FREE(s, p) {if (p) ZFREE(s, p);}
 
+/* Reverse the bytes in a 64-bit or 32-bit or 16-bit value */
+#if defined(_WIN32) && (_MSC_VER >= 1300) && (defined(_M_IX86) || defined(_M_X64))
+#  include <stdlib.h>
+#  pragma intrinsic(_byteswap_ulong)
+#  define ZSWAP32(q) _byteswap_ulong(q)
+#elif defined(__GNUC__) && ((__GNUC__ > 4) || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
+#  include <byteswap.h>
+#  define ZSWAP32(q) __builtin_bswap32(q)
+#else
+#  define ZSWAP32(q) ((((q) >> 24) & 0xff) + (((q) >> 8) & 0xff00) + \
+                              (((q) & 0xff00) << 8) + (((q) & 0xff) << 24))
+#endif
+
 #endif /* ZUTIL_H */