Rework swapping code.

1 files changed, 350 insertions, 0 deletions

diff --git a/elfcpp/elfcpp_swap.h b/elfcpp/elfcpp_swap.h
new file mode 100644
index 0000000..979108e
--- /dev/null
+++ b/elfcpp/elfcpp_swap.h
@@ -0,0 +1,350 @@
+// elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
+
+// This header file defines basic template classes to efficiently swap
+// numbers between host form and target form.  When the host and
+// target have the same endianness, these turn into no-ops.
+
+#ifndef ELFCPP_SWAP_H
+#define ELFCPP_SWAP_H
+
+#include <stdint.h>
+#include <endian.h>
+#include <byteswap.h>
+
+namespace elfcpp
+{
+
+// Endian simply indicates whether the host is big endian or not.
+
+struct Endian
+{
+ public:
+  // Used for template specializations.
+  static const bool host_big_endian = __BYTE_ORDER == __BIG_ENDIAN;
+};
+
+// Valtype_base is a template based on size (8, 16, 32, 64) which
+// defines the type Valtype as the unsigned integer of the specified
+// size.
+
+template<int size>
+struct Valtype_base;
+
+template<>
+struct Valtype_base<8>
+{
+  typedef unsigned char Valtype;
+};
+
+template<>
+struct Valtype_base<16>
+{
+  typedef uint16_t Valtype;
+};
+
+template<>
+struct Valtype_base<32>
+{
+  typedef uint32_t Valtype;
+};
+
+template<>
+struct Valtype_base<64>
+{
+  typedef uint64_t Valtype;
+};
+
+// Convert_endian is a template based on size and on whether the host
+// and target have the same endianness.  It defines the type Valtype
+// as Valtype_base does, and also defines a function convert_host
+// which takes an argument of type Valtype and returns the same value,
+// but swapped if the host and target have different endianness.
+
+template<int size, bool same_endian>
+struct Convert_endian;
+
+template<int size>
+struct Convert_endian<size, true>
+{
+  typedef typename Valtype_base<size>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  { return v; }
+};
+
+template<>
+struct Convert_endian<8, false>
+{
+  typedef Valtype_base<8>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  { return v; }
+};
+
+template<>
+struct Convert_endian<16, false>
+{
+  typedef Valtype_base<16>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  { return bswap_16(v); }
+};
+
+template<>
+struct Convert_endian<32, false>
+{
+  typedef Valtype_base<32>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  { return bswap_32(v); }
+};
+
+template<>
+struct Convert_endian<64, false>
+{
+  typedef Valtype_base<64>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  { return bswap_64(v); }
+};
+
+// Convert is a template based on size and on whether the target is
+// big endian.  It defines Valtype and convert_host like
+// Convert_endian.  That is, it is just like Convert_endian except in
+// the meaning of the second template parameter.
+
+template<int size, bool big_endian>
+struct Convert
+{
+  typedef typename Valtype_base<size>::Valtype Valtype;
+
+  static inline Valtype
+  convert_host(Valtype v)
+  {
+    return Convert_endian<size, big_endian == Endian::host_big_endian>
+      ::convert_host(v);
+  }
+};
+
+// Swap is a template based on size and on whether the target is big
+// endian.  It defines the type Valtype and the functions readval and
+// writeval.  The functions read and write values of the appropriate
+// size out of buffers, swapping them if necessary.  readval and
+// writeval are overloaded to take pointers to the appropriate type or
+// pointers to unsigned char.
+
+template<int size, bool big_endian>
+struct Swap
+{
+  typedef typename Valtype_base<size>::Valtype Valtype;
+
+  static inline Valtype
+  readval(const Valtype* wv)
+  { return Convert<size, big_endian>::convert_host(*wv); }
+
+  static inline void
+  writeval(Valtype* wv, Valtype v)
+  { *wv = Convert<size, big_endian>::convert_host(v); }
+
+  static inline Valtype
+  readval(const unsigned char* wv)
+  { return readval(reinterpret_cast<const Valtype*>(wv)); }
+
+  static inline void
+  writeval(unsigned char* wv, Valtype v)
+  { writeval(reinterpret_cast<Valtype*>(wv), v); }
+};
+
+// We need to specialize the 8-bit version of Swap to avoid
+// conflicting overloads, since both versions of readval and writeval
+// will have the same type parameters.
+
+template<bool big_endian>
+struct Swap<8, big_endian>
+{
+  typedef typename Valtype_base<8>::Valtype Valtype;
+
+  static inline Valtype
+  readval(const Valtype* wv)
+  { return *wv; }
+
+  static inline void
+  writeval(Valtype* wv, Valtype v)
+  { *wv = v; }
+};
+
+// Swap_unaligned is a template based on size and on whether the
+// target is big endian.  It defines the type Valtype and the
+// functions readval_unaligned and writeval_unaligned.  The functions
+// read and write values of the appropriate size out of buffers which
+// may be misaligned.
+
+template<int size, bool big_endian>
+struct Swap_unaligned;
+
+template<bool big_endian>
+struct Swap_unaligned<8, big_endian>
+{
+  typedef typename Valtype_base<8>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  { return *wv; }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  { *wv = v; }
+};
+
+template<>
+struct Swap_unaligned<16, false>
+{
+  typedef Valtype_base<16>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return (wv[1] << 8) | wv[0];
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[1] = v >> 8;
+    wv[0] = v;
+  }
+};
+
+template<>
+struct Swap_unaligned<16, true>
+{
+  typedef Valtype_base<16>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return (wv[0] << 8) | wv[1];
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[0] = v >> 8;
+    wv[1] = v;
+  }
+};
+
+template<>
+struct Swap_unaligned<32, false>
+{
+  typedef Valtype_base<32>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return (wv[3] << 24) | (wv[2] << 16) | (wv[1] << 8) | wv[0];
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[3] = v >> 24;
+    wv[2] = v >> 16;
+    wv[1] = v >> 8;
+    wv[0] = v;
+  }
+};
+
+template<>
+struct Swap_unaligned<32, true>
+{
+  typedef Valtype_base<32>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return (wv[0] << 24) | (wv[1] << 16) | (wv[2] << 8) | wv[3];
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[0] = v >> 24;
+    wv[1] = v >> 16;
+    wv[2] = v >> 8;
+    wv[3] = v;
+  }
+};
+
+template<>
+struct Swap_unaligned<64, false>
+{
+  typedef Valtype_base<64>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return ((static_cast<Valtype>(wv[7]) << 56)
+	    | (static_cast<Valtype>(wv[6]) << 48)
+	    | (static_cast<Valtype>(wv[5]) << 40)
+	    | (static_cast<Valtype>(wv[4]) << 32)
+	    | (static_cast<Valtype>(wv[3]) << 24)
+	    | (static_cast<Valtype>(wv[2]) << 16)
+	    | (static_cast<Valtype>(wv[1]) << 8)
+	    | static_cast<Valtype>(wv[0]));
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[7] = v >> 56;
+    wv[6] = v >> 48;
+    wv[5] = v >> 40;
+    wv[4] = v >> 32;
+    wv[3] = v >> 24;
+    wv[2] = v >> 16;
+    wv[1] = v >> 8;
+    wv[0] = v;
+  }
+};
+
+template<>
+struct Swap_unaligned<64, true>
+{
+  typedef Valtype_base<64>::Valtype Valtype;
+
+  static inline Valtype
+  readval_unaligned(const unsigned char* wv)
+  {
+    return ((static_cast<Valtype>(wv[0]) << 56)
+	    | (static_cast<Valtype>(wv[1]) << 48)
+	    | (static_cast<Valtype>(wv[2]) << 40)
+	    | (static_cast<Valtype>(wv[3]) << 32)
+	    | (static_cast<Valtype>(wv[4]) << 24)
+	    | (static_cast<Valtype>(wv[5]) << 16)
+	    | (static_cast<Valtype>(wv[6]) << 8)
+	    | static_cast<Valtype>(wv[7]));
+  }
+
+  static inline void
+  writeval_unaligned(unsigned char* wv, Valtype v)
+  {
+    wv[7] = v >> 56;
+    wv[6] = v >> 48;
+    wv[5] = v >> 40;
+    wv[4] = v >> 32;
+    wv[3] = v >> 24;
+    wv[2] = v >> 16;
+    wv[1] = v >> 8;
+    wv[0] = v;
+  }
+};
+
+} // End namespace elfcpp.
+
+#endif // !defined(ELFCPP_SWAP_H)