sparse_bsearch: new module

ccan/sparse_bsearch/_info

+#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;
+}

ccan/sparse_bsearch/sparse_bsearch.c

+#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;
+}

ccan/sparse_bsearch/sparse_bsearch.h

+#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 */

ccan/sparse_bsearch/test/run.c

+/* 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();
+}