Implement a sparse array / set.

CMakeLists.txt

@@ -4,7 +4,7 @@ project(libds)
 set_property(GLOBAL PROPERTY C_STANDARD 90)
 ADD_COMPILE_OPTIONS(-pedantic -Wall)
 
-add_library(ds STATIC src/libds.c src/vec.c src/ht.c src/ll.c)
+add_library(ds STATIC src/libds.c src/vec.c src/ht.c src/ll.c src/sprs.c)
 add_executable(libds src/main.c)
 
 target_include_directories(ds PUBLIC include)

include/sprs.h

@@ -0,0 +1,142 @@
+#ifndef LIBDS_SPRS_HEADER
+#define LIBDS_SPRS_HEADER
+
+#include "libds.h"
+
+/**
+ * Sparse set implementation with the capacity to store data.
+ * Sparse sets are initially defined as having two arrays of integers,
+ * one "dense" array, into which new elements are added sequentially, and another
+ * "sparse" array into which the elements' indexes in the dense array are put at
+ * their index.
+ *
+ * For instance, after adding the elements 1, 0, and 3 to a sparse array,
+ * it may look like:
+ *           (Size)    (Capacity)
+ *             |           |
+ * [1 ][0 ][3 ][..][..][..] (Dense)
+ * [1 ][0 ][..][2 ][..][..] (Sparse)
+ * As seen in the above representation, the element in the dense array at index 0 is 1,
+ * and the element at index 1 in the sparse array points to its location in the dense array.
+ * It's very quick to check whether an element is part of this sparse set:
+ * if sparse[element] < size && dense[sparse[element]] == element.
+ * Iteration is also O(n), thanks to the dense array, and no initial memory clearing is required.
+ *
+ * The below implementation adds an additional piece of data to the sparse array, a void* so that an item
+ * can be associated with an integer index and stored / retrieved / ismember'ed together with it.
+ */
+
+/**
+ * A single element in a sparse array.
+ */
+struct sprs_element_s {
+  /**
+   * The index of this element in the dense array.
+   */
+  int index;
+  /**
+   * A piece of data (optional) associated with this index.
+   */
+  void* data;
+};
+
+/**
+ * A sparse array / set.
+ */
+struct sprs_s {
+  /**
+   * The maximum size of the set. This is the limit for integer indices.
+   */
+  int capacity;
+  /**
+   * The current size of the sparse set, and the next available index in the dense array.
+   */
+  int size;
+
+  /**
+   * The dense array.
+   * This is a pointer so that an array of a certain size can be allocated as needed.
+   */
+  int* dense;
+  /**
+   * The sparse array.
+   * This is a pointer so that an array of a certain size can be allocated as needed.
+   */
+  struct sprs_element_s* sparse;
+};
+
+typedef struct sprs_s sprs;
+
+/**
+ * Initializes a sparse set with default values.
+ * This does not allocate any memory for the arrays.
+ * @param sprs the sparse set / array to initialize.
+ */
+void sprs_init(sprs* sprs);
+/**
+ * Allocates the necessary memory for a sparse set's
+ * dense and sparse arrays.
+ * @param sprs the sparse set for which memory should be allocated.
+ * @param size the maximum capacity of the sparse set to use.
+ * @return LIBDS_SUCCESS if all goes well, or LIBDS_MALLOC if an allocation failed.
+ */
+libds_result sprs_setup(sprs* sprs, int size);
+/**
+ * Frees memory allocated by the sparse set, and resets its capacity and size.
+ * @param sprs the sparse set to free.
+ */
+void sprs_free(sprs* sprs);
+
+/**
+ * Stores a value in the sparse set under a given index.
+ * @param sprs the sparse set into which to store the value.
+ * @param index the index at which to store the value
+ * @param data the value to store.
+ */
+void sprs_put(sprs* sprs, int index, void* data);
+/**
+ * Checks if the sparse set contains data under a given index.
+ * @param sprs the sparse set to check.
+ * @param index the index for which to check.
+ * @return 1 if the index exists, 0 if not.
+ */
+int sprs_contains(sprs* sprs, int index);
+/**
+ * Gets the value stored under the given sparse set index.
+ * This will check for whether the index is in the sparse set first,
+ * and return NULL if it's not.
+ * Please not that this exhibit the !exact same! behavior if a NULL was stored
+ * under the index or if the index was never populated. use sprs_contains to
+ * check whether the index is populated if this is important.
+ * @param sprs the sparse set to check.
+ * @param index the index from under which to retrieve the value.
+ * @return the value stored under the index, or NULL if there is nothing there.
+ */
+void* sprs_get(sprs* sprs, int index);
+
+/**
+ * Runs through every element in the sparse set, and compares it against the
+ * given data using the given comparison function. If the comparison function returns
+ * true, returns the element that was passed to it. If the comparison function returns
+ * true for no element, returns NULL.
+ * @param sprs the sparse set to iterate through.
+ * @param data the data to compare elements against
+ * @param compare the comparison function
+ * @return the first element that is matched by the comparison function, or NULL if none are matched.
+ */
+void* sprs_find(sprs* sprs, void* data, compare_func compare);
+/**
+ * Runs through every element in the sparse set, and compares it against the
+ * given data using the given comparison function. If the comparison function returns
+ * true, calls the foreach function, passing it the element and the variable argument list.
+ * Stops if any foreach function returns a nonzero code.
+ * @param sprs the sparse set to perform the operation on
+ * @param data the data to pass the comparison function
+ * @param compare the comparison function operating on the data and each element in the list.
+ * @param foreach the function to be called on every element recognized by the comparison function
+ * @param ... variable arguments to be passed on to the foreach function
+ * @return 0 if all goes well, or the first nonzero code returned by foreach.
+ */
+int sprs_foreach(sprs* sprs, void* data, compare_func compare, foreach_func foreach, ...);
+
+#endif

src/sprs.c

@@ -0,0 +1,70 @@
+#include "sprs.h"
+#include <stdlib.h>
+
+void sprs_init(sprs* sprs){
+  sprs->capacity = 0;
+  sprs->size = 0;
+  sprs->dense = NULL;
+  sprs->sparse = NULL;
+}
+libds_result sprs_setup(sprs* sprs, int size){
+  libds_result result = LIBDS_SUCCESS;
+  sprs->sparse = malloc(sizeof(*(sprs->sparse)) * size);
+  sprs->dense = malloc(sizeof(*(sprs->dense)) * size);
+  if(sprs->sparse == NULL || sprs->dense == NULL){
+    free(sprs->sparse);
+    free(sprs->dense);
+    result = LIBDS_MALLOC;
+  } else {
+    sprs->capacity = size;
+  }
+  return result;
+}
+void sprs_free(sprs* sprs){
+  free(sprs->sparse);
+  free(sprs->dense);
+  sprs->capacity = 0;
+  sprs->size = 0;
+  sprs->dense = NULL;
+  sprs->sparse = NULL;
+}
+void sprs_put(sprs* sprs, int index, void* data){
+  if(index < sprs->capacity && sprs->size < sprs->capacity){
+    sprs->dense[sprs->size++] = index;
+    sprs->sparse[index].index = sprs->size - 1;
+    sprs->sparse[index].data = data;
+  }
+}
+int sprs_contains(sprs* sprs, int index){
+  return sprs->sparse[index].index < sprs->size && sprs->dense[sprs->sparse[index].index] == index;
+}
+void* sprs_get(sprs* sprs, int index){
+  void* data = NULL;
+  if(sprs_contains(sprs, index)){
+    data = sprs->sparse[index].data;
+  }
+  return data;
+}
+void* sprs_find(sprs* sprs, void* data, compare_func compare){
+  int index = 0;
+  void* to_return = NULL;
+  for(; index < sprs->size && to_return == NULL; index++){
+    if(compare(data, sprs->sparse[sprs->dense[index]].data)) {
+      to_return = sprs->sparse[sprs->dense[index]].data;
+    }
+  }
+  return to_return;
+}
+int sprs_foreach(sprs* sprs, void* data, compare_func compare, foreach_func foreach, ...){
+  int index = 0;
+  int return_code = 0;
+  va_list args;
+  for(; index < sprs->size && return_code == 0; index++){
+    if(compare(data, sprs->sparse[sprs->dense[index]].data)) {
+      va_start(args, foreach);
+      return_code = foreach(sprs->sparse[sprs->dense[index]].data, args);
+      va_end(args);
+    }
+  }
+  return return_code;
+}