implemented bounded_bitset::find_first(...)

lib/include/srsran/adt/bounded_bitset.h

@@ -26,6 +26,31 @@ constexpr uint32_t ceil_div(uint32_t x, uint32_t y)
   return (x + y - 1) / y;
 }
 
+template <typename Integer>
+Integer mask_trailing_ones(size_t N)
+{
+  static_assert(std::is_unsigned<Integer>::value, "T must be unsigned integer");
+  return N == 0 ? 0 : (static_cast<Integer>(-1) >> (sizeof(Integer) * 8U - N));
+}
+
+template <typename Integer>
+Integer mask_leading_ones(size_t N)
+{
+  return ~mask_trailing_ones<Integer>(8U * sizeof(Integer) - N);
+}
+
+template <typename Integer>
+Integer mask_trailing_zeros(size_t N)
+{
+  return mask_leading_ones<Integer>(8U * sizeof(Integer) - N);
+}
+
+template <typename Integer>
+Integer mask_leading_zeros(size_t N)
+{
+  return mask_trailing_ones<Integer>(8U * sizeof(Integer) - N);
+}
+
 template <size_t N, bool reversed = false>
 class bounded_bitset
 {
@@ -100,8 +125,7 @@ public:
 
   bounded_bitset<N, reversed>& fill(size_t startpos, size_t endpos, bool value = true)
   {
-    assert_within_bounds_(startpos, false);
-    assert_within_bounds_(endpos, false);
+    assert_range_bounds_(startpos, endpos);
     // NOTE: can be optimized
     if (value) {
       for (size_t i = startpos; i < endpos; ++i) {
@@ -115,6 +139,37 @@ public:
     return *this;
   }
 
+  int find_first(size_t startpos, size_t endpos, bool value = true) const noexcept
+  {
+    assert_range_bounds_(startpos, endpos);
+    if (startpos == endpos) {
+      return -1;
+    }
+
+    size_t startword = startpos / bits_per_word;
+    size_t lastword  = (endpos - 1) / bits_per_word;
+
+    for (size_t i = startword; i <= lastword; ++i) {
+      word_t w = buffer[i];
+      if (not value) {
+        w = ~w;
+      }
+
+      if (i == startword) {
+        size_t offset = startpos % bits_per_word;
+        w &= mask_trailing_zeros<word_t>(offset);
+      }
+      if (i == lastword) {
+        size_t offset = (endpos - 1) % bits_per_word;
+        w &= mask_trailing_ones<word_t>(offset + 1);
+      }
+      if (w != 0) {
+        return static_cast<int>(i * bits_per_word + (bits_per_word - __builtin_clzl(w) - 1));
+      }
+    }
+    return -1;
+  }
+
   bool all() const noexcept
   {
     const size_t nw = nof_words_();
@@ -307,6 +362,15 @@ private:
                   size());
   }
 
+  void assert_range_bounds_(size_t startpos, size_t endpos) const
+  {
+    srsran_assert(startpos <= endpos and endpos <= size(),
+                  "ERROR: range [%zd, %zd) out-of-bounds for bitsize of size=%zd",
+                  startpos,
+                  endpos,
+                  size());
+  }
+
   static word_t maskbit(size_t pos) { return (static_cast<word_t>(1)) << (pos % bits_per_word); }
 
   static size_t max_nof_words_() { return (N - 1) / bits_per_word + 1; }

lib/test/adt/bounded_bitset_test.cc

@@ -13,6 +13,14 @@
 #include "srsran/adt/bounded_bitset.h"
 #include "srsran/common/test_common.h"
 
+void test_bit_operations()
+{
+  TESTASSERT(0 == srsran::mask_trailing_ones<uint32_t>(0));
+  TESTASSERT(0b11 == srsran::mask_trailing_ones<uint32_t>(2));
+  TESTASSERT(0b11111111 == srsran::mask_trailing_ones<uint8_t>(8));
+  TESTASSERT(0b1111 == srsran::mask_trailing_ones<uint8_t>(4));
+}
+
 int test_zero_bitset()
 {
   srsran::bounded_bitset<25> mask;
@@ -176,14 +184,34 @@ int test_bitset_resize()
   return SRSRAN_SUCCESS;
 }
 
+void test_bitset_find()
+{
+  {
+    srsran::bounded_bitset<25> bitset(6);
+    bitset.set(2);
+    TESTASSERT(bitset.find_first(0, 6) == 2);
+    TESTASSERT(bitset.find_first(3, 6) == -1);
+    bitset.set(5);
+    TESTASSERT(bitset.find_first(3, 6) == 5);
+  }
+  {
+    srsran::bounded_bitset<100> bitset(95);
+    bitset.set(94);
+    TESTASSERT(bitset.find_first(0, 93) == -1);
+    TESTASSERT(bitset.find_first(0, bitset.size()) == 94);
+  }
+}
+
 int main()
 {
+  test_bit_operations();
   TESTASSERT(test_zero_bitset() == SRSRAN_SUCCESS);
   TESTASSERT(test_ones_bitset() == SRSRAN_SUCCESS);
   TESTASSERT(test_bitset_set() == SRSRAN_SUCCESS);
   TESTASSERT(test_bitset_bitwise_oper() == SRSRAN_SUCCESS);
   TESTASSERT(test_bitset_print() == SRSRAN_SUCCESS);
   TESTASSERT(test_bitset_resize() == SRSRAN_SUCCESS);
+  test_bitset_find();
   printf("Success\n");
   return 0;
 }