Add a new method roaring_bitmap_range_bool_array.

.gitignore

@@ -40,6 +40,8 @@ tests/config.h
 # CMake
 build
 
+# clangd
+.cache/clangd/
 
 
 #############BEGIN VISUAL STUDIO############

README.md

@@ -805,6 +805,39 @@ You should be aware that a convention bitset (`bitset_t *`) may use much more
 memory than a Roaring bitmap in some cases. You should run benchmarks to determine
 whether the conversion to a bitset has performance benefits in your case.
 
+
+# Convert to boolean array (C)
+
+This example shows how to convert a range of a Roaring bitmap to a boolean array using `roaring_bitmap_range_bool_array`:
+
+```c
+roaring_bitmap_t *r1 = roaring_bitmap_create();
+for (uint32_t i = 100; i < 100000; i+= 1 + (i%5)) {
+     roaring_bitmap_add(r1, i);
+}
+for (uint32_t i = 100000; i < 500000; i+= 100) {
+     roaring_bitmap_add(r1, i);
+}
+roaring_bitmap_add_range(r1, 500000, 600000);
+
+// Convert a range to boolean array
+uint32_t range_start = 50;  // Start from the 50th element
+uint32_t range_end = 1000; // End at the 1000th element (not included)
+bool *bool_array = malloc((range_end - range_start) * sizeof(bool));
+
+// Convert range to boolean array
+roaring_bitmap_range_bool_array(r1, range_start, range_end, bool_array);
+
+// The bool_array now contains true/false for elements at positions [range_start, range_end)
+// bool_array[i] is true if the (range_start+i) exists in the bitmap
+
+// you must free the memory:
+free(bool_array);
+roaring_bitmap_free(r1);
+```
+
+This function stores each element's presence in a single byte as a boolean value, which can be useful when you need to work with boolean arrays directly for a specific range of the bitmap.
+
 # Example (C++)
 
 

benchmarks/bitset_container_benchmark.c

@@ -6,7 +6,7 @@
 #include "benchmark.h"
 #include "random.h"
 
-#define DIV_CEIL_64K(denom) (((1 << 16) + ((denom)-1)) / (denom))
+#define DIV_CEIL_64K(denom) (((1 << 16) + ((denom) - 1)) / (denom))
 
 const int repeat = 500;
 

include/roaring/containers/array.h

@@ -466,6 +466,20 @@ inline int array_container_index_equalorlarger(const array_container_t *arr,
     }
 }
 
+/**
+ * Reads values from the array container into a boolean buffer.
+ *
+ * @param ac The array container to read from
+ * @param it Iterator state (index into the array)
+ * @param buf Boolean buffer to write to
+ * @param max_value Stop reading when it->current_value >= this value.
+ * @param value_out Output parameter for the next value
+ * @return true if there are more values to read, false otherwise
+ */
+bool array_container_iterator_read_into_bool(
+    const array_container_t *ac, struct roaring_container_iterator_s *it,
+    bool *buf, uint32_t max_value, uint16_t *value_out);
+
 /*
  * Adds all values in range [min,max] using hint:
  *   nvals_less is the number of array values less than $min

include/roaring/containers/bitset.h

@@ -505,6 +505,20 @@ int bitset_container_get_index(const bitset_container_t *container, uint16_t x);
 int bitset_container_index_equalorlarger(const bitset_container_t *container,
                                          uint16_t x);
 
+/**
+ * Reads values from the bitset container into a boolean buffer.
+ *
+ * @param bc The bitset container to read from
+ * @param it Iterator state (index into the bitset)
+ * @param buf Boolean buffer to write to
+ * @param max_value Stop reading when it->current_value >= this value.
+ * @param value_out Output parameter for the next value
+ * @return true if there are more values to read, false otherwise
+ */
+bool bitset_container_iterator_read_into_bool(
+    const bitset_container_t *bc, struct roaring_container_iterator_s *it,
+    bool *buf, uint32_t max_value, uint16_t *value_out);
+
 #ifdef __cplusplus
 }
 }

include/roaring/containers/containers.h

@@ -2477,6 +2477,24 @@ bool container_iterator_read_into_uint64(const container_t *c, uint8_t typecode,
                                          uint32_t count, uint32_t *consumed,
                                          uint16_t *value_out);
 
+/**
+ * Iterate all entries within [it->current_value, max_value), and sets
+ * corresponding positions in `buf` to true.
+ *
+ * The `buf` array is filled starting from index 0, which corresponds to the
+ * initial iterator position `it`. For subsequent iterator positions `it_new`,
+ * set `buf[it_new->current_value - it->current_value]` to true.
+ *
+ * Returns true and sets `value_out` if a value is present after reading the
+ * entries.
+ *
+ * The initial `it` should have a value.
+ */
+bool container_iterator_read_into_bool(const container_t *c, uint8_t typecode,
+                                       roaring_container_iterator_t *it,
+                                       bool *buf, uint32_t max_value,
+                                       uint16_t *value_out);
+
 /**
  * Skips the next `skip_count` entries in the container iterator. Returns true
  * and sets `value_out` if a value is present after skipping. Returns false if

include/roaring/containers/run.h

@@ -46,7 +46,7 @@ typedef struct rle16_s rle16_t;
 
 #ifdef __cplusplus
 #define CROARING_MAKE_RLE16(val, len) \
-    { (uint16_t)(val), (uint16_t)(len) }  // no tagged structs until c++20
+    {(uint16_t)(val), (uint16_t)(len)}  // no tagged structs until c++20
 #else
 #define CROARING_MAKE_RLE16(val, len) \
     (rle16_t) { .value = (uint16_t)(val), .length = (uint16_t)(len) }
@@ -709,6 +709,20 @@ static inline void run_container_remove_range(run_container_t *run,
     }
 }
 
+/**
+ * Reads values from the run container into a boolean buffer.
+ *
+ * @param rc The run container to read from
+ * @param it Iterator state (index into the runs array)
+ * @param buf Boolean buffer to write to
+ * @param max_value Stop reading when it->current_value >= this value.
+ * @param value_out Output parameter for the current/next value
+ * @return true if there are more values to read, false otherwise
+ */
+bool run_container_iterator_read_into_bool(
+    const run_container_t *rc, struct roaring_container_iterator_s *it,
+    bool *buf, uint32_t max_value, uint16_t *value_out);
+
 #ifdef __cplusplus
 }
 }

include/roaring/roaring.h

@@ -555,6 +555,24 @@ void roaring_bitmap_to_uint32_array(const roaring_bitmap_t *r, uint32_t *ans);
  */
 bool roaring_bitmap_to_bitset(const roaring_bitmap_t *r, bitset_t *bitset);
 
+/**
+ * Convert the bitmap within the range [range_start, range_end) to a dense bool
+ * array and output in `ans`.
+ *
+ * For each value at position `i` (where i ranges from 0 to
+ * range_end-range_start) in the output array, `ans[i]` is set to true if the
+ * (range_start + i)-th element in the bitmap exists, and false otherwise.
+ *
+ * Caller is responsible to ensure that there is enough memory allocated, e.g.
+ *
+ *     ans = malloc((range_end - range_start) * sizeof(bool));
+ *
+ * For more control, see `roaring_uint32_iterator_move_equalorlarger` and
+ * `roaring_uint32_iterator_read_into_bool`.
+ */
+void roaring_bitmap_range_bool_array(const roaring_bitmap_t *r,
+                                     uint32_t range_start, uint32_t range_end,
+                                     bool *ans);
 /**
  * Convert the bitmap to a sorted array from `offset` by `limit`, output in
  * `ans`.
@@ -1208,6 +1226,35 @@ CROARING_DEPRECATED static inline void roaring_free_uint32_iterator(
 uint32_t roaring_uint32_iterator_read(roaring_uint32_iterator_t *it,
                                       uint32_t *buf, uint32_t count);
 
+/**
+ * Iterate over `it` in range [it->current_value, max_value) and fill bool array
+ * `buf` from its beginning.
+ *
+ * This function satisfies semantics of iteration and can be used together with
+ * other iterator functions.
+ *
+ * Let `init_it` be the initial iterator and it has value, then for every
+ * iterated `it`, buf[init_it.current_value - it.current_value] will be set to
+ * true; other positions will remain to be false. The final `it` will be invalid
+ * or point to the first value >= max_value.
+ *
+ * User should ensure that `buf` has enough space for holding the bool values.
+ *
+ * Here is an example:
+ *                                     final_it(8)
+ *                         init_it(4)  max_value(8)
+ *                              │       │
+ *                              ▼       ▼
+ *              Values:   1 2 3 4 5 6 7 8 9
+ *              Roaring:    x   x     x x x
+ * The result bool array:      [1 0 0 1]
+ * Size of the bool array: 4    ▲
+ *                              │
+ *                 Beginning of the bool array
+ */
+void roaring_uint32_iterator_read_into_bool(roaring_uint32_iterator_t *it,
+                                            bool *buf, uint32_t max_value);
+
 /** DEPRECATED, use `roaring_uint32_iterator_read`. */
 CROARING_DEPRECATED static inline uint32_t roaring_read_uint32_iterator(
     roaring_uint32_iterator_t *it, uint32_t *buf, uint32_t count) {

microbenchmarks/bench.cpp

@@ -237,6 +237,21 @@ struct to_array64 {
 auto ToArray64 = BasicBench<to_array64>;
 BENCHMARK(ToArray64);
 
+struct to_array_bool {
+    static uint64_t run() {
+        uint64_t marker = 0;
+        for (size_t i = 0; i < count; ++i) {
+            uint64_t card = roaring_bitmap_get_cardinality(bitmaps[i]);
+            roaring_bitmap_range_bool_array(bitmaps[i], 0, card,
+                                            array_buffer_bool);
+            marker += array_buffer_bool[0];
+        }
+        return marker;
+    }
+};
+auto ToArrayBool = BasicBench<to_array_bool>;
+BENCHMARK(ToArrayBool);
+
 struct iterate_all {
     static uint64_t run() {
         uint64_t marker = 0;

microbenchmarks/bench.h

@@ -42,6 +42,7 @@ roaring64_bitmap_t **bitmaps64 = NULL;
 Roaring64Map **bitmaps64cpp = NULL;
 uint32_t *array_buffer;
 uint64_t *array_buffer64;
+bool *array_buffer_bool;
 uint32_t maxvalue = 0;
 uint32_t maxcard = 0;
 
@@ -200,6 +201,7 @@ static roaring_bitmap_t **create_all_bitmaps(size_t *howmany,
     }
     array_buffer = (uint32_t *)malloc(maxcard * sizeof(uint32_t));
     array_buffer64 = (uint64_t *)malloc(maxcard * sizeof(uint64_t));
+    array_buffer_bool = (bool *)malloc(maxvalue + 1);
     return answer;
 }
 

src/containers/array.c

@@ -562,6 +562,34 @@ bool array_container_iterate64(const array_container_t *cont, uint32_t base,
     return true;
 }
 
+CROARING_ALLOW_UNALIGNED
+bool array_container_iterator_read_into_bool(const array_container_t *ac,
+                                             roaring_container_iterator_t *it,
+                                             bool *buf, uint32_t max_value,
+                                             uint16_t *value_out) {
+    int32_t initial_index = it->index;
+
+    if (max_value > UINT16_MAX) {
+        // TODO: SIMD optimization
+        while (it->index < ac->cardinality) {
+            buf[ac->array[it->index] - ac->array[initial_index]] = true;
+            it->index++;
+        }
+        return false;
+    }
+
+    while (it->index < ac->cardinality &&
+           (uint32_t)ac->array[it->index] < max_value) {
+        buf[ac->array[it->index] - ac->array[initial_index]] = true;
+        it->index++;
+    }
+    if (it->index < ac->cardinality) {
+        *value_out = ac->array[it->index];
+        return true;
+    }
+    return false;
+}
+
 #ifdef __cplusplus
 }
 }

src/containers/bitset.c

@@ -245,6 +245,55 @@ bool bitset_container_intersect(const bitset_container_t *src_1,
     return false;
 }
 
+CROARING_ALLOW_UNALIGNED
+bool bitset_container_iterator_read_into_bool(const bitset_container_t *bc,
+                                              roaring_container_iterator_t *it,
+                                              bool *buf, uint32_t max_value,
+                                              uint16_t *value_out) {
+    uint32_t max_wordindex = max_value / 64;
+    if (max_wordindex >= BITSET_CONTAINER_SIZE_IN_WORDS) {
+        max_wordindex = BITSET_CONTAINER_SIZE_IN_WORDS - 1;
+    }
+    uint32_t wordindex = it->index / 64;
+    uint64_t word = bc->words[wordindex] & (UINT64_MAX << (it->index % 64));
+    uint16_t initial_value = it->index;
+    // Remain the last word to process out of loop for reducing `if` branches
+    while (wordindex < max_wordindex) {
+        // TODO: SIMD optimization
+        while (word != 0) {
+            it->index = wordindex * 64 + roaring_trailing_zeroes(word);
+            buf[it->index - initial_value] = true;
+            word = word & (word - 1);
+        }
+        wordindex++;
+        if (wordindex < BITSET_CONTAINER_SIZE_IN_WORDS) {
+            word = bc->words[wordindex];
+        }
+    }
+    // Process the last word (which is at max_wordindex)
+    while (word != 0) {
+        it->index = wordindex * 64 + roaring_trailing_zeroes(word);
+        if ((uint32_t)it->index >= max_value) {
+            *value_out = it->index;
+            return true;
+        }
+        buf[it->index - initial_value] = true;
+        word = word & (word - 1);
+    }
+
+    /// If the bitset is not drained, iterate to the next set bit.
+    while (word == 0 && (wordindex + 1 < BITSET_CONTAINER_SIZE_IN_WORDS)) {
+        wordindex++;
+        word = bc->words[wordindex];
+    }
+    if (word != 0) {
+        it->index = wordindex * 64 + roaring_trailing_zeroes(word);
+        *value_out = it->index;
+        return true;
+    }
+    return false;
+}
+
 #if CROARING_IS_X64
 #ifndef CROARING_WORDS_IN_AVX2_REG
 #define CROARING_WORDS_IN_AVX2_REG sizeof(__m256i) / sizeof(uint64_t)

src/containers/containers.c

@@ -706,6 +706,28 @@ bool container_iterator_read_into_uint64(const container_t *c, uint8_t typecode,
     }
 }
 
+bool container_iterator_read_into_bool(const container_t *c, uint8_t typecode,
+                                       roaring_container_iterator_t *it,
+                                       bool *buf, uint32_t max_value,
+                                       uint16_t *value_out) {
+    c = container_unwrap_shared(c, &typecode);
+    switch (typecode) {
+        case BITSET_CONTAINER_TYPE:
+            return bitset_container_iterator_read_into_bool(
+                const_CAST_bitset(c), it, buf, max_value, value_out);
+        case ARRAY_CONTAINER_TYPE:
+            return array_container_iterator_read_into_bool(
+                const_CAST_array(c), it, buf, max_value, value_out);
+        case RUN_CONTAINER_TYPE:
+            return run_container_iterator_read_into_bool(
+                const_CAST_run(c), it, buf, max_value, value_out);
+        default:
+            assert(false);
+            roaring_unreachable;
+            return false;
+    }
+}
+
 bool container_iterator_skip(const container_t *c, uint8_t typecode,
                              roaring_container_iterator_t *it,
                              uint32_t skip_count, uint32_t *consumed_count,