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+.TH IPSEC_RANGETOSUBNET 3 "8 Sept 2000"
+.\" RCSID $Id: rangetosubnet.3,v 1.1 2004/03/15 20:35:26 as Exp $
+.SH NAME
+ipsec rangetosubnet \- convert address range to subnet
+.SH SYNOPSIS
+.B "#include <freeswan.h>"
+.sp
+.B "const char *rangetosubnet(const ip_address *start,"
+.ti +1c
+.B "const ip_address *stop, ip_subnet *dst);"
+.SH DESCRIPTION
+.I Rangetosubnet
+accepts two IP addresses which define an address range,
+from
+.I start
+to
+.I stop
+inclusive,
+and converts this to a subnet if possible.
+The addresses must both be IPv4 or both be IPv6,
+and the address family of the resulting subnet is the same.
+.PP
+.I Rangetosubnet
+returns NULL for success and
+a pointer to a string-literal error message for failure;
+see DIAGNOSTICS.
+.SH SEE ALSO
+ipsec_initsubnet(3), ipsec_ttosubnet(3)
+.SH DIAGNOSTICS
+Fatal errors in
+.I rangetosubnet
+are:
+mixed address families;
+unknown address family;
+.I start
+and
+.I stop
+do not define a subnet.
+.SH HISTORY
+Written for the FreeS/WAN project by Henry Spencer.
+.SH BUGS
+The restriction of error reports to literal strings
+(so that callers don't need to worry about freeing them or copying them)
+does limit the precision of error reporting.
+.PP
+The error-reporting convention lends itself
+to slightly obscure code,
+because many readers will not think of NULL as signifying success.
+A good way to make it clearer is to write something like:
+.PP
+.RS
+.nf
+.B "const char *error;"
+.sp
+.B "error = rangetosubnet( /* ... */ );"
+.B "if (error != NULL) {"
+.B "        /* something went wrong */"
+.fi
+.RE