Add the QP interface as a possible replacement for patricia tries.

For "quadbit patricia tries", inspired by the work of Tony Finch:
https://dotat.at/prog/qp/README.html

Radix 16 tries, examining a nibble at a time, to make the tries
smaller and reduce pointer chasing.

configure.ac

@@ -78,6 +78,9 @@ AC_FUNC_REALLOC
 AC_TYPE_SIZE_T
 AC_TYPE_UINT64_T
 
+# Check if gcc has this builtin (clang has a has_builtin() macro).
+AX_GCC_BUILTIN(__builtin_popcount)
+
 # --enable-stack-protector
 AC_ARG_ENABLE(stack-protector,
        AS_HELP_STRING([--enable-stack-protector],[enable stack protector (default is YES)]),

src/Makefile.am

@@ -8,7 +8,10 @@ vmod_LTLIBRARIES = libvmod_selector.la
 libvmod_selector_la_SOURCES = \
 	vmod_selector.c \
 	patricia.h \
-	patricia.c
+	patricia.c \
+	qp.h \
+	qp.c \
+	popcnt_compat.h
 
 nodist_libvmod_selector_la_SOURCES = \
 	vcc_if.c \
@@ -22,6 +25,8 @@ dist_man_MANS = vmod_selector.3
 
 vmod_selector.c patricia.c: patricia.h
 
+qp.c: qp.h popcnt_compat.h
+
 vmod_selector.lo: $(nodist_libvmod_selector_la_SOURCES)
 
 vcc_if.h vmod_selector.rst vmod_selector.man.rst: vcc_if.c

src/popcnt_compat.h

+/*-
+ * Copyright (c) 2020 UPLEX Nils Goroll Systemoptimierung
+ * All rights reserved
+ *
+ * Author: Geoffrey Simmons <geoffrey.simmons@uplex.de>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#ifndef __has_builtin
+#define __has_builtin(b) 0
+#endif
+
+#if defined(__POPCNT__) && \
+	(HAVE___BUILTIN_POPCOUNT || __has_builtin(__builtin_popcount))
+
+static inline int
+popcount (unsigned int x)
+{
+	return (__builtin_popcount(x));
+}
+
+#else
+
+/* Table from Stanford Bit Twiddling Hacks */
+
+static const unsigned char popcnt_tbl[256] = 
+{
+#   define B2(n) n,     n+1,     n+1,     n+2
+#   define B4(n) B2(n), B2(n+1), B2(n+1), B2(n+2)
+#   define B6(n) B4(n), B4(n+1), B4(n+1), B4(n+2)
+    B6(0), B6(1), B6(1), B6(2)
+};
+
+static inline int
+popcount(uint16_t n)
+{
+	return (popcnt_tbl[n >> 8] + popcnt_tbl[n & 0xff]);
+}
+
+#endif

src/qp.h

+/*-
+ * Copyright (c) 2020 UPLEX Nils Goroll Systemoptimierung
+ * All rights reserved
+ *
+ * Author: Geoffrey Simmons <geoffrey.simmons@uplex.de>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <limits.h>
+#include <unistd.h>
+
+#include "vsb.h"
+
+struct pt_y;
+
+struct match_data {
+	unsigned	magic;
+#define MATCH_DATA_MAGIC 0x0d9a845e
+	unsigned	*indices;
+	unsigned	limit;
+	unsigned	n;
+	unsigned	exact;
+	unsigned	min;
+	unsigned	max;
+};
+
+struct qp_stats {
+	unsigned	magic;
+#define QP_STATS_MAGIC 0x06d2b30c
+	uint64_t	nodes;
+	uint64_t	leaves;
+	uint64_t	terms;
+	uint64_t	nodesz;
+	uint64_t	dmin;
+	uint64_t	dmax;
+	double		davg;
+	uint64_t	fmin;
+	uint64_t	fmax;
+	double		favg;
+};
+
+int QP_Insert(struct pt_y * * restrict root, unsigned idx,
+	      char * const restrict * const restrict strings);
+unsigned QP_Lookup(const struct pt_y * const restrict root,
+		   char * const restrict * const restrict strings,
+		   const char * const restrict subject);
+int QP_Prefixes(const struct pt_y * const restrict root,
+		char * const restrict * const restrict strings,
+		const char * const restrict subject,
+		struct match_data * const restrict match);
+void QP_Stats(const struct pt_y * const restrict root,
+	      char * const restrict * const restrict strings,
+	      struct qp_stats * const restrict stats);
+void QP_Free(struct pt_y *y);
+struct vsb * QP_Dump(struct pt_y *root, char **strings);