System: Add SwapByteOrder and update Support/MathExtras.h to use it.

This time correctly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116247 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 101 insertions, 0 deletions

diff --git a/include/llvm/System/SwapByteOrder.h b/include/llvm/System/SwapByteOrder.h
new file mode 100644
index 0000000000..64a8acb019
--- /dev/null
+++ b/include/llvm/System/SwapByteOrder.h
@@ -0,0 +1,101 @@
+//===- SwapByteOrder.h - Generic and optimized byte swaps -------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares generic and optimized functions to swap the byte order of
+// an integral type.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SYSTEM_SWAP_BYTE_ORDER_H
+#define LLVM_SYSTEM_SWAP_BYTE_ORDER_H
+
+#include "llvm/Support/type_traits.h"
+#include "llvm/System/DataTypes.h"
+#include <cstddef>
+#include <limits>
+
+namespace llvm {
+namespace sys {
+
+template<typename value_type>
+inline
+typename enable_if_c<sizeof(value_type) == 1
+                     && std::numeric_limits<value_type>::is_integer,
+                     value_type>::type
+SwapByteOrder(value_type Value) {
+  // No swapping needed.
+  return Value;
+}
+
+template<typename value_type>
+inline
+typename enable_if_c<sizeof(value_type) == 2
+                     && std::numeric_limits<value_type>::is_integer,
+                     value_type>::type
+SwapByteOrder(value_type Value) {
+  // Cast signed types to unsigned before swapping.
+  uint16_t value = static_cast<uint16_t>(Value);
+#if defined(_MSC_VER) && !defined(_DEBUG)
+  // The DLL version of the runtime lacks these functions (bug!?), but in a
+  // release build they're replaced with BSWAP instructions anyway.
+  return _byteswap_ushort(value);
+#else
+  uint16_t Hi = value << 8;
+  uint16_t Lo = value >> 8;
+  return value_type(Hi | Lo);
+#endif
+}
+
+template<typename value_type>
+inline
+typename enable_if_c<sizeof(value_type) == 4
+                     && std::numeric_limits<value_type>::is_integer,
+                     value_type>::type
+SwapByteOrder(value_type Value) {
+  // Cast signed types to unsigned before swapping.
+  uint32_t value = static_cast<uint32_t>(Value);
+#if defined(__llvm__) || \
+    (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)) && !defined(__ICC)
+  return __builtin_bswap32(value);
+#elif defined(_MSC_VER) && !defined(_DEBUG)
+  return _byteswap_ulong(value);
+#else
+  uint32_t Byte0 = value & 0x000000FF;
+  uint32_t Byte1 = value & 0x0000FF00;
+  uint32_t Byte2 = value & 0x00FF0000;
+  uint32_t Byte3 = value & 0xFF000000;
+  return value_type(
+    (Byte0 << 24) | (Byte1 << 8) | (Byte2 >> 8) | (Byte3 >> 24));
+#endif
+}
+
+template<typename value_type>
+inline
+typename enable_if_c<sizeof(value_type) == 8
+                     && std::numeric_limits<value_type>::is_integer,
+                     value_type>::type
+SwapByteOrder(value_type Value) {
+  // Cast signed types to unsigned before swapping.
+  uint64_t value = static_cast<uint64_t>(Value);
+#if defined(__llvm__) || \
+    (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)) && !defined(__ICC)
+  return __builtin_bswap64(value);
+#elif defined(_MSC_VER) && !defined(_DEBUG)
+  return _byteswap_uint64(value);
+#else
+  uint64_t Hi = SwapByteOrder<uint32_t>(uint32_t(value));
+  uint32_t Lo = SwapByteOrder<uint32_t>(uint32_t(value >> 32));
+  return value_type((Hi << 32) | Lo);
+#endif
+}
+
+} // end namespace sys
+} // end namespace llvm
+
+#endif