Use uint64_t array and fewer branches in BitSet

ConflictSet.cpp

@@ -93,62 +93,47 @@ private:
 };
 
 struct BitSet {
-  bool test(int i) const {
-    assert(0 <= i);
-    assert(i < 256);
-    if (i < 128) {
-      return (lo >> i) & 1;
-    } else {
-      return (hi >> (i - 128)) & 1;
-    }
-  }
-
-  void set(int i) {
-    assert(0 <= i);
-    assert(i < 256);
-    if (i < 128) {
-      lo |= __uint128_t(1) << i;
-    } else {
-      hi |= __uint128_t(1) << (i - 128);
-    }
-  }
-
-  void reset(int i) {
-    assert(0 <= i);
-    assert(i < 256);
-    if (i < 128) {
-      lo &= ~(__uint128_t(1) << i);
-    } else {
-      hi &= ~(__uint128_t(1) << (i - 128));
-    }
-  }
-
-  int firstSetGeq(int i) const {
-    assert(0 <= i);
-    if (i >= 256) {
-      return -1;
-    }
-    if (i < 128) {
-      int a = std::countr_zero(lo >> i);
-      if (a < 128) {
-        assert(i + a < 128);
-        return i + a;
-      }
-      i = 128;
-    }
-    int b = std::countr_zero(hi >> (i - 128));
-    if (b < 128) {
-      assert(i + b < 256);
-      return i + b;
-    }
-    return -1;
-  }
+  bool test(int i) const;
+  void set(int i);
+  void reset(int i);
+  int firstSetGeq(int i) const;
 
 private:
-  __uint128_t lo = 0;
-  __uint128_t hi = 0;
+  uint64_t words[4] = {};
 };
 
+bool BitSet::test(int i) const {
+  assert(0 <= i);
+  assert(i < 256);
+  return words[i >> 6] & (uint64_t(1) << (i & 63));
+}
+
+void BitSet::set(int i) {
+  assert(0 <= i);
+  assert(i < 256);
+  words[i >> 6] |= uint64_t(1) << (i & 63);
+}
+
+void BitSet::reset(int i) {
+  assert(0 <= i);
+  assert(i < 256);
+  words[i >> 6] &= ~(uint64_t(1) << (i & 63));
+}
+
+int BitSet::firstSetGeq(int i) const {
+  assert(0 <= i);
+  // i may be >= 256
+  uint64_t mask = uint64_t(-1) << (i & 63);
+  for (int j = i >> 6; j < 4; ++j) {
+    uint64_t masked = mask & words[j];
+    if (masked) {
+      return (j << 6) + std::countr_zero(masked);
+    }
+    mask = -1;
+  }
+  return -1;
+}
+
 enum class Type : int8_t {
   Node4,
   Node16,