Move bsearch_arg to src/port

Until now the bsearch_arg function was used only in extended statistics
code, so it was defined in that code.  But we already have qsort_arg in
src/port, so let's move it next to it.

src/port/Makefile

@@ -40,6 +40,7 @@ LIBS += $(PTHREAD_LIBS)
 OBJS = \
 	$(LIBOBJS) \
 	$(PG_CRC32C_OBJS) \
+	bsearch_arg.o \
 	chklocale.o \
 	erand48.o \
 	inet_net_ntop.o \

src/port/bsearch_arg.c

@@ -0,0 +1,78 @@
+/*
+ * bsearch_arg.c: bsearch variant with a user-supplied pointer
+ *
+ * Copyright (c) 2021, PostgreSQL Global Development Group
+ * Copyright (c) 1990 Regents of the University of California.
+ * All rights reserved.
+ *
+ * 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.
+ * 3. [rescinded 22 July 1999]
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 THE REGENTS 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.
+ *
+ * src/port/bsearch_arg.c
+ */
+
+#include "c.h"
+
+/*
+ * Perform a binary search.
+ *
+ * The code below is a bit sneaky.  After a comparison fails, we
+ * divide the work in half by moving either left or right. If lim
+ * is odd, moving left simply involves halving lim: e.g., when lim
+ * is 5 we look at item 2, so we change lim to 2 so that we will
+ * look at items 0 & 1.  If lim is even, the same applies.  If lim
+ * is odd, moving right again involes halving lim, this time moving
+ * the base up one item past p: e.g., when lim is 5 we change base
+ * to item 3 and make lim 2 so that we will look at items 3 and 4.
+ * If lim is even, however, we have to shrink it by one before
+ * halving: e.g., when lim is 4, we still looked at item 2, so we
+ * have to make lim 3, then halve, obtaining 1, so that we will only
+ * look at item 3.
+ */
+void *
+bsearch_arg(const void *key, const void *base0,
+			size_t nmemb, size_t size,
+			int (*compar) (const void *, const void *, void *),
+			void *arg)
+{
+	const char *base = (const char *) base0;
+	int			lim,
+				cmp;
+	const void *p;
+
+	for (lim = nmemb; lim != 0; lim >>= 1)
+	{
+		p = base + (lim >> 1) * size;
+		cmp = (*compar) (key, p, arg);
+		if (cmp == 0)
+			return (void *) p;
+		if (cmp > 0)
+		{						/* key > p: move right */
+			base = (const char *) p + size;
+			lim--;
+		}						/* else move left */
+	}
+	return (NULL);
+}