rework the page a bit, clarify a few things, maybe better wording

src/lib/libc/crypt/crypt_checkpass.3

@@ -1,4 +1,4 @@
-.\" $OpenBSD: crypt_checkpass.3,v 1.9 2015/07/23 22:20:02 tedu Exp $
+.\" $OpenBSD: crypt_checkpass.3,v 1.10 2017/07/22 03:23:48 tedu Exp $
 .\"
 .\" Copyright (c) 2014 Ted Unangst <tedu@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: July 23 2015 $
+.Dd $Mdocdate: July 22 2017 $
 .Dt CRYPT_CHECKPASS 3
 .Os
 .Sh NAME
@@ -30,7 +30,7 @@
 .Sh DESCRIPTION
 The
 .Fn crypt_checkpass
-function is provided to simplify checking a user's password.
+function simplifies checking a user's password.
 If both the
 .Fa hash
 and the
@@ -53,11 +53,15 @@ A failure will return \-1 and set
 .Pp
 The
 .Fn crypt_newhash
-function is provided to simplify the creation of new password hashes.
+function simplifies the creation of new password hashes.
 The provided
 .Fa password
 is randomly salted and hashed and stored in
 .Fa hash .
+The size of the available space is specified by
+.Fa hashsize ,
+which should be
+.Dv _PASSWORD_LEN .
 The
 .Fa pref
 argument identifies the preferred hashing algorithm and parameters.
@@ -66,9 +70,10 @@ Possible values are:
 .It Dq bcrypt,<rounds>
 The bcrypt algorithm, where the value of rounds can be between 4 and 31 and
 specifies the base 2 logarithm of the number of rounds.
-The special rounds value
-.Sq a
-automatically selects rounds based on system performance.
+If rounds is omitted or the special value 
+.Sq a ,
+an appropriate number of rounds is automatically selected based on system
+performance.
 .El
 .Sh RETURN VALUES
 .Rv -std crypt_checkpass crypt_newhash
@@ -89,7 +94,7 @@ to
 .Er EINVAL
 if
 .Fa pref
-is unsupported.
+is unsupported or insufficient space is provided.
 .Sh SEE ALSO
 .Xr crypt 3 ,
 .Xr login.conf 5 ,