/*------------------------------------------------------------------
 * strfirstdiff_s.c
 *
 * November 2008, Bo Berry
 *
 * Copyright (c) 2008-2011 by Cisco Systems, Inc
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *------------------------------------------------------------------
 */

#include "safeclib_private.h"
#include "safe_str_constraint.h"
#include "safe_str_lib.h"


/**
 * NAME
 *    strfirstdiff_s
 *
 * SYNOPSIS
 *    #include "safe_str_lib.h"
 *    errno_t
 *    strfirstdiff_s(const char *dest, rsize_t dmax,
 *                   const char *src, rsize_t *index)
 *
 * DESCRIPTION
 *    Returns the index of the first character that is different
 *    between dest and src. Index is valid only for OK.
 *    The scanning stops at the first null in dest or src, or
 *    after dmax characters.
 *
 * EXTENSION TO
 *    ISO/IEC TR 24731, Programming languages, environments
 *    and system software interfaces, Extensions to the C Library,
 *    Part I: Bounds-checking interfaces
 *
 * INPUT PARAMETERS
 *    dest     pointer to string to compare against
 *
 *    dmax     restricted maximum length of string dest
 *
 *    src      pointer to the string to be compared to dest
 *
 *    index    pointer to returned index to first difference
 *
 * OUTPUT PARAMETERS
 *    index    returned index to first difference
 *
 * RUNTIME CONSTRAINTS
 *    Neither dest nor src shall be a null pointer.
 *    indicator shall not be a null pointer.
 *    dmax shall not be 0.
 *    dmax shall not be greater than RSIZE_MAX_STR.
 *
 * RETURN VALUE
 *    index to first difference, when the return code is OK
 *
 *    EOK         index to first diff is returned
 *    ESNODIFF    no difference
 *    ESNULLP     NULL pointer
 *    ESZEROL     zero length
 *    ESLEMAX     length exceeds max limit
 *
 * ALSO SEE
 *    strfirstchar_s(), strfirstsame_s(), strlastchar_s(),
 *    strlastdiff_s(), strlastsame_s()
 *
 */
 errno_t
 strfirstdiff_s (const char *dest, rsize_t dmax,
                 const char *src, rsize_t *index)
{
    const char *rp;

    if (index == NULL) {
        invoke_safe_str_constraint_handler("strfirstdiff_s: index is null",
                   NULL, ESNULLP);
        return (ESNULLP);
    }
    *index = 0;

    if (dest == NULL) {
        invoke_safe_str_constraint_handler("strfirstdiff_s: dest is null",
                   NULL, ESNULLP);
        return (ESNULLP);
    }

    if (src == NULL) {
        invoke_safe_str_constraint_handler("strfirstdiff_s: src is null",
                   NULL, ESNULLP);
        return (ESNULLP);
    }

    if (dmax == 0 ) {
        invoke_safe_str_constraint_handler("strfirstdiff_s: dmax is 0",
                   NULL, ESZEROL);
        return (ESZEROL);
    }

    if (dmax > RSIZE_MAX_STR) {
        invoke_safe_str_constraint_handler("strfirstdiff_s: dmax exceeds max",
                   NULL, ESLEMAX);
        return (ESLEMAX);
    }

    /* hold reference point */
    rp = dest;

    while (*dest && *src && dmax) {

        if (*dest != *src) {
            *index = dest - rp;
            return (EOK);
        }
        dmax--;
        dest++;
        src++;
    }

    return (ESNODIFF);
}
