/* Compare strings while treating digits characters numerically.
   2    Copyright (C) 1997-2016 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jean-François Bignolles <bignolle@ecoledoc.ibp.fr>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */

#include "strverscmp.h"

#include <stdint.h>
#include <string.h>
#include <ctype.h>

/* states: S_N: normal, S_I: comparing integral part, S_F: comparing
           fractionnal parts, S_Z: idem but with leading Zeroes only */
#define  S_N    0x0
#define  S_I    0x3
#define  S_F    0x6
#define  S_Z    0x9

/* result_type: CMP: return diff; LEN: compare using len_diff/diff */
#define  CMP    2
#define  LEN    3

/* Compare S1 and S2 as strings holding indices/version numbers,
   returning less than, equal to or greater than zero if S1 is less than,
   equal to or greater than S2 (for more info, see the texinfo doc).
*/

int strverscmp (const char *s1, const char *s2)
{
 const unsigned char *p1 = (const unsigned char *) s1;
 const unsigned char *p2 = (const unsigned char *) s2;

 /* Symbol(s)    0       [1-9]   others
    Transition   (10) 0  (01) d  (00) x   */
 static const uint8_t next_state[] =
 {
     /* state    x    d    0  */
     /* S_N */  S_N, S_I, S_Z,
     /* S_I */  S_N, S_I, S_I,
     /* S_F */  S_N, S_F, S_F,
     /* S_Z */  S_N, S_F, S_Z
 };

 static const int8_t result_type[] =
 {
     /* state   x/x  x/d  x/0  d/x  d/d  d/0  0/x  0/d  0/0  */

     /* S_N */  CMP, CMP, CMP, CMP, LEN, CMP, CMP, CMP, CMP,
     /* S_I */  CMP, -1,  -1,  +1,  LEN, LEN, +1,  LEN, LEN,
     /* S_F */  CMP, CMP, CMP, CMP, CMP, CMP, CMP, CMP, CMP,
     /* S_Z */  CMP, +1,  +1,  -1,  CMP, CMP, -1,  CMP, CMP
 };

 if (p1 == p2)
   return 0;

 unsigned char c1 = *p1++;
 unsigned char c2 = *p2++;
 /* Hint: '0' is a digit too.  */
 int state = S_N + ((c1 == '0') + (isdigit (c1) != 0));

 int diff;
 while ((diff = c1 - c2) == 0)
   {
     if (c1 == '\0')
       return diff;

     state = next_state[state];
     c1 = *p1++;
     c2 = *p2++;
     state += (c1 == '0') + (isdigit (c1) != 0);
   }

 state = result_type[state * 3 + (((c2 == '0') + (isdigit (c2) != 0)))];

 switch (state)
 {
   case CMP:
     return diff;

   case LEN:
     while (isdigit (*p1++))
       if (!isdigit (*p2++))
         return 1;

     return isdigit (*p2) ? -1 : diff;

   default:
     return state;
 }
}