bpo-40302: Add pycore_byteswap.h header file (GH-19552)

Add a new internal pycore_byteswap.h header file with the following
functions:

* _Py_bswap16()
* _Py_bswap32()
* _Py_bswap64()

Use these functions in _ctypes, sha256 and sha512 modules,
and also use in the UTF-32 encoder.

sha256, sha512 and _ctypes modules are now built with the internal
C API.

2 files changed, 93 insertions, 4 deletions

diff --git a/Include/internal/pycore_byteswap.h b/Include/internal/pycore_byteswap.h
new file mode 100644
index 0000000..5e64704
--- /dev/null
+++ b/Include/internal/pycore_byteswap.h
@@ -0,0 +1,89 @@
+/* Bytes swap functions, reverse order of bytes:
+
+   - _Py_bswap16(uint16_t)
+   - _Py_bswap32(uint32_t)
+   - _Py_bswap64(uint64_t)
+*/
+
+#ifndef Py_INTERNAL_BSWAP_H
+#define Py_INTERNAL_BSWAP_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+#if defined(__clang__) || \
+    (defined(__GNUC__) && \
+     ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8)))
+   /* __builtin_bswap16() is available since GCC 4.8,
+      __builtin_bswap32() is available since GCC 4.3,
+      __builtin_bswap64() is available since GCC 4.3. */
+#  define _PY_HAVE_BUILTIN_BSWAP
+#endif
+
+#ifdef _MSC_VER
+   /* Get _byteswap_ushort(), _byteswap_ulong(), _byteswap_uint64() */
+#  include <intrin.h>
+#endif
+
+static inline uint16_t
+_Py_bswap16(uint16_t word)
+{
+#ifdef _PY_HAVE_BUILTIN_BSWAP
+    return __builtin_bswap16(word);
+#elif defined(_MSC_VER)
+    Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned short));
+    return _byteswap_ushort(word);
+#else
+    // Portable implementation which doesn't rely on circular bit shift
+    return ( ((word & UINT16_C(0x00FF)) << 8)
+           | ((word & UINT16_C(0xFF00)) >> 8));
+#endif
+}
+
+static inline uint32_t
+_Py_bswap32(uint32_t word)
+{
+#ifdef _PY_HAVE_BUILTIN_BSWAP
+    return __builtin_bswap32(word);
+#elif defined(_MSC_VER)
+    Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned long));
+    return _byteswap_ulong(word);
+#else
+    // Portable implementation which doesn't rely on circular bit shift
+    return ( ((word & UINT32_C(0x000000FF)) << 24)
+           | ((word & UINT32_C(0x0000FF00)) <<  8)
+           | ((word & UINT32_C(0x00FF0000)) >>  8)
+           | ((word & UINT32_C(0xFF000000)) >> 24));
+#endif
+}
+
+static inline uint64_t
+_Py_bswap64(uint64_t word)
+{
+#ifdef _PY_HAVE_BUILTIN_BSWAP
+    return __builtin_bswap64(word);
+#elif defined(_MSC_VER)
+    return _byteswap_uint64(word);
+#else
+    // Portable implementation which doesn't rely on circular bit shift
+    return ( ((word & UINT64_C(0x00000000000000FF)) << 56)
+           | ((word & UINT64_C(0x000000000000FF00)) << 40)
+           | ((word & UINT64_C(0x0000000000FF0000)) << 24)
+           | ((word & UINT64_C(0x00000000FF000000)) <<  8)
+           | ((word & UINT64_C(0x000000FF00000000)) >>  8)
+           | ((word & UINT64_C(0x0000FF0000000000)) >> 24)
+           | ((word & UINT64_C(0x00FF000000000000)) >> 40)
+           | ((word & UINT64_C(0xFF00000000000000)) >> 56));
+#endif
+}
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_BSWAP_H */
+
diff --git a/Include/pyport.h b/Include/pyport.h
index 72e74e0..63d3b81 100644
--- a/Include/pyport.h
+++ b/Include/pyport.h
@@ -768,11 +768,11 @@ extern char * _getpty(int *, int, mode_t, int);
  */
 
 #ifdef WORDS_BIGENDIAN
-#define PY_BIG_ENDIAN 1
-#define PY_LITTLE_ENDIAN 0
+#  define PY_BIG_ENDIAN 1
+#  define PY_LITTLE_ENDIAN 0
 #else
-#define PY_BIG_ENDIAN 0
-#define PY_LITTLE_ENDIAN 1
+#  define PY_BIG_ENDIAN 0
+#  define PY_LITTLE_ENDIAN 1
 #endif
 
 #ifdef Py_BUILD_CORE