/usr/share/calc/help/strncmp is in apcalc-common 2.12.4.4-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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    strncmp - compare two strings up to a specified number of characters 
SYNOPSIS
    strncmp(s1, s2, n)
TYPES
    s1		string
    s2		string
    n		nonnegative integer
    return	integer (1, 0 or -1)
DESCRIPTION
    Let n1 = size(s1), n2 = size(s2) and m = min(n1, n2, n).
    This function compares up to m values of consecutive characters
    in the strings s1 and s2. If an inequality is encountered, the
    function returns 1 or -1 according as the greater character is
    in s1 or s2. If there has been no inequality, the function
    returns 1, 0, or -1 according as min(n1, n) is greater than, equal
    to, or less than min(n2, n); in particular, if n1 and n2 are
    both greater than equal to n, 0 is returned.
 
EXAMPLE
strncmp("abc", "xyz", 0) == 0
strncmp("abc", "xyz", 1) == -1
strncmp("abc", "", 1) == 1
strncmp("a", "b", 2) == -1
strncmp("ab", "ac", 2) == -1
strncmp("\0ac", "\0b", 2) == -1
strncmp("ab", "abc", 2) == 0
strncmp("abc", "abd", 2) == 0
LIMITS
    none
LINK LIBRARY
    This function uses FLAG stringrel(STRING *s1, STRING *s2),
    temporarily replacing the string sizes by min(n1,n) and min(n2,n).
SEE ALSO
    strcat, strcpy, strerror, strlen, strncpy, strpos,
    strprintf, strscan, strscanf, substr
## Copyright (C) 2006  Ernest Bowen
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 59 Temple Place, Suite 330, Boston, MA  02111-1307, USA.
##
## @(#) $Revision: 30.1 $
## @(#) $Id: strncmp,v 30.1 2007/03/16 11:10:42 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/strncmp,v $
##
## Under source code control:	2006/03/03 03:32:44
## File existed as early as:	2006
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
 |