Optimize bit counting using __builtin_popcount

Use the __builtin_popcount intrinsic to optimize the bit counting
function if the compiler supports it. This change replaces the manual
bit counting algorithm with the more efficient built-in function, which
leverages hardware support on compatible processors.

This modification ensures that the code remains backward-compatible by
falling back to the original implementation when __builtin_popcount is
not available.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/afl-fuzz-bitmap.c b/src/afl-fuzz-bitmap.c
index 03bc5d6c..405d2dd6 100644
--- a/src/afl-fuzz-bitmap.c
+++ b/src/afl-fuzz-bitmap.c
@@ -75,9 +75,13 @@ u32 count_bits(afl_state_t *afl, u8 *mem) {
 
     }
 
+#if __has_builtin(__builtin_popcount)
+    ret += __builtin_popcount(v);
+#else
     v -= ((v >> 1) & 0x55555555);
     v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
     ret += (((v + (v >> 4)) & 0xF0F0F0F) * 0x01010101) >> 24;
+#endif
 
   }