[ViewVC] Diff of: cvs/libecb/ecb.h

Comparing libecb/ecb.h (file contents):
Revision 1.204 by root, Fri Mar 25 08:44:14 2022 UTC vs.
Revision 1.205 by root, Fri Mar 25 14:21:14 2022 UTC

     _BitScanForward (&r, x);
     return (int)r;
 #else
     int r = 0;
+    /* todo: use david seal's algorithm */
     x &= ~x + 1; /* this isolates the lowest bit */
 #if ECB_branchless_on_i386
     r += !!(x & 0xaaaaaaaa) << 0;
     r += !!(x & 0xcccccccc) << 1;
   x = ( x >> 16              ) | ( x               << 16);
   return x;
 }
-/* popcount64 is only available on 64 bit cpus as gcc builtin */
-/* so for this version we are lazy */
 ecb_function_ ecb_const int ecb_popcount64 (uint64_t x);
 ecb_function_ ecb_const int
 ecb_popcount64 (uint64_t x)
 {
+  /* popcount64 is only available on 64 bit cpus as gcc builtin. */
+  /* also, gcc/clang make this surprisingly difficult to use */
+#if __LP64__ && (ECB_GCC_VERSION(3,4) || ECB_CLANG_BUILTIN (__builtin_popcountl))
+  return __builtin_popcountl (x);
+#else
   return ecb_popcount32 (x) + ecb_popcount32 (x >> 32);
+#endif
 }
 ecb_inline ecb_const uint8_t  ecb_rotl8  (uint8_t  x, unsigned int count);
 ecb_inline ecb_const uint8_t  ecb_rotr8  (uint8_t  x, unsigned int count);
 ecb_inline ecb_const uint16_t ecb_rotl16 (uint16_t x, unsigned int count);

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