+#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 */