update shift_r8.c example

ilanschnell · Dec 22, 2023 · 2386799 · 2386799
1 parent 3cbb19a
commit 2386799
Showing 1 changed file with 23 additions and 11 deletions.
diff --git a/examples/shift_r8.c b/examples/shift_r8.c
@@ -18,11 +18,23 @@
 
 #define Py_ssize_t ssize_t
 
-#if (defined(__clang__) || defined(__GNUC__))
-#define IS_GNUC 1
+static inline uint64_t
+builtin_bswap64(uint64_t word)
+{
+#if (defined(__clang__) || \
+ (defined(__GNUC__) \
+ && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 3))))
+ /* __builtin_bswap64() is available since GCC 4.3. */
+# define HAVE_BUILTIN_BSWAP64 1
+ return __builtin_bswap64(word);
+#elif defined(_MSC_VER)
+# define HAVE_BUILTIN_BSWAP64 1
+ return _byteswap_uint64(word);
 #else
-#define IS_GNUC 0
+# define HAVE_BUILTIN_BSWAP64 0
+ abort()
 #endif
+}
 
 /* machine byte-order */
 #define PY_LITTLE_ENDIAN 1
@@ -48,7 +60,7 @@ shift_r8le(unsigned char *buff, Py_ssize_t n, int k)
 {
  Py_ssize_t w = 0;
 
-#if IS_GNUC || PY_LITTLE_ENDIAN /* use shift word */
+#if HAVE_BUILTIN_BSWAP64 || PY_LITTLE_ENDIAN /* use shift word */
  w = n / 8; /* number of words used for shifting */
  n %= 8; /* number of remaining bytes */
 #endif
@@ -60,10 +72,10 @@ shift_r8le(unsigned char *buff, Py_ssize_t n, int k)
  }
  while (w--) { /* shift in word-range(0, w) */
  uint64_t *p = ((uint64_t *) buff) + w;
-#if IS_GNUC && PY_BIG_ENDIAN
- *p = __builtin_bswap64(*p);
+#if HAVE_BUILTIN_BSWAP64 && PY_BIG_ENDIAN
+ *p = builtin_bswap64(*p);
  *p <<= k;
- *p = __builtin_bswap64(*p);
+ *p = builtin_bswap64(*p);
 #else
  *p <<= k;
 #endif
@@ -77,7 +89,7 @@ shift_r8be(unsigned char *buff, Py_ssize_t n, int k)
 {
  Py_ssize_t w = 0;
 
-#if IS_GNUC || PY_BIG_ENDIAN /* use shift word */
+#if HAVE_BUILTIN_BSWAP64 || PY_BIG_ENDIAN /* use shift word */
  w = n / 8; /* number of words used for shifting */
  n %= 8; /* number of remaining bytes */
 #endif
@@ -89,10 +101,10 @@ shift_r8be(unsigned char *buff, Py_ssize_t n, int k)
  }
  while (w--) { /* shift in word-range(0, w) */
  uint64_t *p = ((uint64_t *) buff) + w;
-#if IS_GNUC && PY_LITTLE_ENDIAN
- *p = __builtin_bswap64(*p);
+#if HAVE_BUILTIN_BSWAP64 && PY_LITTLE_ENDIAN
+ *p = builtin_bswap64(*p);
  *p >>= k;
- *p = __builtin_bswap64(*p);
+ *p = builtin_bswap64(*p);
 #else
  *p >>= k;
 #endif