--- /dev/null
+#include <string.h>
+#include <stdio.h>
+#include "config.h"
+
+/**
+ * sparse_bsearch - search a sorted array with some invalid entries
+ *
+ * bsearch() is great for searching an array, but if you are deleting from
+ * the array, you then need to memmove() to keep it dense.
+ *
+ * Sometimes there is a useful invalid value which can be used to mark deleted
+ * entries, but such a "gappy" array breaks bsearch. This function allows
+ * "invalid" entries in your array, which are ignored for the search.
+ *
+ * Example:
+ * #include <ccan/sparse_bsearch/sparse_bsearch.h>
+ *
+ * static bool val_valid(unsigned int *val)
+ * {
+ * return *val != 0;
+ * }
+ * static int val_cmp(const unsigned int *a, const unsigned int *b)
+ * {
+ * return (int)((*a) - (*b));
+ * }
+ * static unsigned int values[] = { 1, 7, 11, 1235, 99999 };
+ *
+ * // Return true if this value is in set, and remove it.
+ * bool remove_from_values(unsigned int val)
+ * {
+ * unsigned int *p;
+ * // We use 5 here, but ccan/array_size.h is better!
+ * p = sparse_bsearch(&val, values, 5, val_cmp, val_valid);
+ * if (!p)
+ * return false;
+ * *p = 0;
+ * return true;
+ * }
+ *
+ * int main(int argc, char *argv[])
+ * {
+ * int i, val;
+ * for (i = 1; i < argc; i++) {
+ * val = atoi(argv[i]);
+ * if (remove_from_values(val))
+ * printf("%i removed.\n", val);
+ * else
+ * printf("%i wasn't there.\n", val);
+ * }
+ * return 0;
+ * }
+ */
+int main(int argc, char *argv[])
+{
+ /* Expect exactly one argument */
+ if (argc != 2)
+ return 1;
+
+ if (strcmp(argv[1], "depends") == 0) {
+ printf("ccan/typesafe_cb\n"
+ "ccan/check_type\n");
+ return 0;
+ }
+
+ return 1;
+}
--- /dev/null
+#include "sparse_bsearch.h"
+
+void *_sparse_bsearch(const void *key, const void *base,
+ size_t nmemb, size_t size,
+ int (*cmpfn)(const void *, const void *),
+ bool (*validfn)(const void *))
+{
+ ssize_t start = 0, end = nmemb - 1;
+ const char *p = base;
+
+ while (start <= end) {
+ ssize_t next = (start + end) / 2;
+ int result;
+
+ while (!validfn(p + next * size)) {
+ /* Try the next one along. */
+ next++;
+ if (next > end) {
+ /* Hmm, none of these were valid. */
+ next = (start + end) / 2;
+ goto trim;
+ }
+ }
+
+ result = cmpfn(key, p + next * size);
+ if (result == 0)
+ return (void *)(p + next * size);
+ else if (result > 0)
+ start = next + 1;
+ else {
+ trim:
+ end = next - 1;
+ }
+ }
+ return NULL;
+}
--- /dev/null
+#ifndef SPARSE_BSEARCH_H
+#define SPARSE_BSEARCH_H
+#include <stdbool.h>
+#include <stdlib.h>
+#include <ccan/typesafe_cb/typesafe_cb.h>
+#include <ccan/check_type/check_type.h>
+
+/**
+ * sparse_bsearch - binary search of a sorted array with gaps.
+ * @key: the key to search for
+ * @base: the head of the array
+ * @nmemb: the number of elements in the array
+ * @cmpfn: the compare function (qsort/bsearch style)
+ * @validfn: whether this element is valid.
+ *
+ * Binary search of a sorted array, which may have some invalid entries.
+ *
+ * Example:
+ * static bool val_valid(unsigned int *val)
+ * {
+ * return *val != 0;
+ * }
+ * static int val_cmp(const unsigned int *a, const unsigned int *b)
+ * {
+ * return (int)((*a) - (*b));
+ * }
+ * static unsigned int values[] = { 1, 7, 11, 1235, 99999 };
+ *
+ * // Return true if this value is in set, and remove it.
+ * bool remove_from_values(unsigned int val)
+ * {
+ * unsigned int *p;
+ * p = sparse_bsearch(&val, values, 5, val_cmp, val_valid);
+ * if (!p)
+ * return false;
+ * *p = 0;
+ * return true;
+ * }
+ */
+#define sparse_bsearch(key, base, nmemb, cmpfn, validfn) \
+ _sparse_bsearch((key)+check_types_match((key), &(base)[0]), \
+ (base), (nmemb), sizeof((base)[0]), \
+ typesafe_cb_cmp(int, (cmpfn), (base)), \
+ typesafe_cb_const(bool, (validfn), (base)))
+
+void *_sparse_bsearch(const void *key, const void *base,
+ size_t nmemb, size_t size,
+ int (*cmpfn)(const void *, const void *),
+ bool (*validfn)(const void *));
+#endif /* SPARSE_BSEARCH_H */
--- /dev/null
+/* Include the main header first, to test it works */
+#include <ccan/sparse_bsearch/sparse_bsearch.h>
+/* Include the C files directly. */
+#include <ccan/sparse_bsearch/sparse_bsearch.c>
+#include <ccan/tap/tap.h>
+
+static int cmp(const unsigned int *a, const unsigned int *b)
+{
+ return (*a) - (*b);
+}
+
+static bool valid(const unsigned int *a)
+{
+ return *a != 0;
+}
+
+int main(void)
+{
+ unsigned int i, j, master[4] = { 1, 2, 3, 4 }, arr[4];
+
+ plan_tests((1 << 4) * 4+ (1 << 3) * 3);
+
+ /* We test all possibilities of an even and an odd array len. */
+ for (i = 0; i < (1 << 4); i++) {
+ /* Setup partial arr[] */
+ for (j = 0; j < 4; j++) {
+ if (i & (1 << j))
+ arr[j] = master[j];
+ else
+ arr[j] = 0;
+ }
+
+ for (j = 1; j <= 4; j++) {
+ unsigned int *ptr;
+ ptr = sparse_bsearch(&j, arr, 4, cmp, valid);
+ if (i & (1 << (j-1)))
+ ok1(ptr && *ptr == j);
+ else
+ ok1(!ptr);
+ }
+ }
+
+ for (i = 0; i < (1 << 3); i++) {
+ /* Setup partial arr[] */
+ for (j = 0; j < 3; j++) {
+ if (i & (1 << j))
+ arr[j] = master[j];
+ else
+ arr[j] = 0;
+ }
+
+ for (j = 1; j <= 3; j++) {
+ unsigned int *ptr;
+ ptr = sparse_bsearch(&j, arr, 3, cmp, valid);
+ if (i & (1 << (j-1)))
+ ok1(ptr && *ptr == j);
+ else
+ ok1(!ptr);
+ }
+ }
+
+ /* This exits depending on whether all tests passed */
+ return exit_status();
+}
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