order: Module for comparison callbacks

Many common algorithms take a callback for comparing items - effectively
giving the items a user defined order.

For example, the standard library qsort() and bsearch() routines take such
a callback.  The ccan/avl module takes an identical one.  The ccan/asort
and ccan/asearch modules use a different variant: their callback takes an
additional context parameter, and is also typed via use of macros and
typesafe_cb.

This module provides helper types and macros for easily declaring any of
the common variants on comparison functions: the 2-parameter untyped form
(as used by qsort), the 3-parameter untyped form (used by the asort back
end) and the 3-parameter typed form (used by the asort front end).  It
provides a wrapper macro for doing the typesafe_cb conversion from
3-parameter typed to 3-parameter untyped.

It also provides a container struct to describe both a comparison callback
and a context value as a single structure.  This also comes in both
untyped and typed variants.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/order/LICENSE

@@ -0,0 +1 @@
+../../licenses/CC0

ccan/order/_info

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+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * order - Simple, common value comparison functions
+ *
+ * This implements a number of commonly useful comparison functions in
+ * a form which can be used with qsort() and bsearch() in the standard
+ * library, or asort() and asearch() in ccan amongst other places.
+ *
+ * License: CC0
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ */
+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");
+		return 0;
+	}
+	if (strcmp(argv[1], "testdepends") == 0) {
+		return 0;
+	}
+
+	return 1;
+}

ccan/order/order.h

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+/* CC0 license (public domain) - see LICENSE file for details */
+#ifndef CCAN_ORDER_H
+#define CCAN_ORDER_H
+
+#include <stdint.h>
+#include <assert.h>
+
+#include <ccan/typesafe_cb/typesafe_cb.h>
+
+typedef int (*_total_order_cb)(const void *, const void *, void *);
+typedef int (*total_order_noctx_cb)(const void *, const void *);
+
+#define total_order_cb(_name, _item, _ctx)		\
+	int (*_name)(const __typeof__(_item) *,		\
+		     const __typeof__(_item) *,		\
+		     __typeof__(_ctx))
+
+#define total_order_cast(cmp, item, ctx)				\
+	typesafe_cb_cast(_total_order_cb, total_order_cb(, item, ctx),	\
+			 (cmp))
+
+struct _total_order {
+	_total_order_cb cb;
+	void *ctx;
+};
+
+#define total_order(_name, _item, _ctx)			\
+	struct {					\
+		total_order_cb(cb, _item, _ctx);	\
+		_ctx ctx;				\
+	} _name
+
+#endif /* CCAN_ORDER_H */

ccan/order/test/compile_fail_1.c

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+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include <ccan/order/order.h>
+
+#include "fancy_cmp.h"
+
+#ifdef FAIL
+typedef int item_t;
+#else
+typedef struct item item_t;
+#endif
+
+int main(int argc, char *argv[])
+{
+	total_order_cb(cb0, struct item, struct cmp_info *) = fancy_cmp;
+	_total_order_cb cb1 = total_order_cast(fancy_cmp,
+					       item_t, struct cmp_info *);
+
+	printf("%p %p\n", cb0, cb1);
+
+	exit(0);
+}

ccan/order/test/compile_fail_2.c

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+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include <ccan/order/order.h>
+
+#include "fancy_cmp.h"
+
+#ifdef FAIL
+typedef int ctx_t;
+#else
+typedef struct cmp_info ctx_t;
+#endif
+
+int main(int argc, char *argv[])
+{
+	total_order_cb(cb0, struct item, struct cmp_info *) = fancy_cmp;
+	_total_order_cb cb1 = total_order_cast(fancy_cmp, struct item,
+					       ctx_t *);
+
+	printf("%p %p\n", cb0, cb1);
+
+	exit(0);
+
+}

ccan/order/test/compile_ok.c

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+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include <ccan/order/order.h>
+
+#include "fancy_cmp.h"
+
+int main(int argc, char *argv[])
+{
+	total_order_cb(cb0, struct item, struct cmp_info *) = fancy_cmp;
+	_total_order_cb cb1 = total_order_cast(fancy_cmp,
+					       struct item, struct cmp_info *);
+	total_order_noctx_cb cb_noctx = fancy_cmp_noctx;
+
+	printf("%p %p %p\n", cb0, cb1, cb_noctx);
+
+	exit(0);
+}

ccan/order/test/fancy_cmp.h

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+#ifndef _FANCY_CMP_H
+#define _FANCY_CMP_H
+
+struct cmp_info {
+	unsigned xcode;
+	int offset;
+};
+
+struct item {
+	unsigned value;
+	char *str;
+};
+
+static inline int fancy_cmp(const struct item *a, const struct item *b,
+			    struct cmp_info *ctx)
+{
+	unsigned vala = a->value ^ ctx->xcode;
+	unsigned valb = b->value ^ ctx->xcode;
+	const char *stra, *strb;
+
+	if (vala < valb)
+		return -1;
+	else if (valb < vala)
+		return 1;
+
+	stra = a->str + ctx->offset;
+	strb = b->str + ctx->offset;
+
+	return strcmp(stra, strb);
+}
+
+static inline int fancy_cmp_noctx(const void *av, const void *bv)
+{
+	const struct item *a = (const struct item *)av;
+	const struct item *b = (const struct item *)bv;
+	struct cmp_info ctx_default = {
+		.xcode = 0x1234,
+		.offset = 3,
+	};
+	total_order(default_order, struct item, struct cmp_info *) = {
+		fancy_cmp, &ctx_default,
+	};
+
+	return default_order.cb(a, b, default_order.ctx);
+}
+
+#endif /* _FANCY_CMP_H */