add bswap32/bswap64

include/bitops-emulated/generic-bswap.h

@@ -0,0 +1,38 @@
+/* generic-bswap.h - generic bswap implementations.
+ *
+ * Copyright (C) 2024 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+#ifndef _GENERIC_BSWAP_H_
+#define _GENERIC_BSWAP_H_
+
+#include "brlib.h"
+
+/* Adapted from: http://www-graphics.stanford.edu/%7Eseander/bithacks.html
+ */
+static __always_inline u32 __bswap32_emulated(u32 n)
+{
+   const u32 k = 0x00FF00FF;
+   n = ((n >>  8) & k) | ((n & k) <<  8);
+   n = ( n >> 16)      | ( n      << 16);
+   return n;
+}
+
+static __always_inline u64 __bswap64_emulated(u64 n)
+{
+   const u64 k1 = 0x00FF00FF00FF00FFull;
+   const u64 k2 = 0x0000FFFF0000FFFFull;
+   n = ((n >>  8) & k1) | ((n & k1) <<  8);
+   n = ((n >> 16) & k2) | ((n & k2) << 16);
+   n = ( n >> 32)       | ( n       << 32);
+   return n;
+}
+
+#endif  /* _GENERIC_BSWAP_H_ */

include/bitops.h

@@ -16,6 +16,7 @@
 #include "brlib.h"
 #include "bitops-emulated/generic-ctz.h"
 #include "bitops-emulated/generic-clz.h"
+#include "bitops-emulated/generic-bswap.h"
 
 #ifndef __has_builtin
 #define __has_builtin(x) 0
@@ -35,7 +36,9 @@
 #if __has_builtin(__builtin_ffs)
 #   define HAS_FFS
 #endif
-
+#if __has_builtin(__builtin_bswap32)
+#   define HAS_BSWAP
+#endif
 
 /**
  * print_bitops_impl() - print bitops implementation.
@@ -174,6 +177,24 @@ void print_bitops_impl(void);
 #define ffz32(n)  ffs32(~(n))
 #define ffz64(n)  ffs64(~(n))
 
+/**
+ * bswap32, bswap64 - reverse bytes: 0x01020304 -> 0x04030201
+ * @n: unsigned 32 or 64 bits integer.
+ *
+ * ffs(n) is similar to ctz(n) + 1, but returns 0 if n == 0 (except
+ * for ctz version, where ffs(0) is undefined).
+ * ffz(n) is ffz(~n), with undefine value if n = 0.
+ */
+#if defined(HAS_BSWAP)
+#   define __bswap32_native(n)  __builtin_bswap32(n)
+#   define __bswap64_native(n)  __builtin_bswap64(n)
+#   define bswap32(n) __bswap32_native(n)
+#   define bswap64(n) __bswap64_native(n)
+#else
+#   define bswap32(n) __bswap32_emulated(n)
+#   define bswap64(n) __bswap64_emulated(n)
+#endif
+
 /**
  * fls32, fls64 - return one plus MSB index: 00101000 -> 6
  * @n: unsigned 32 or 64 bits integer.