Построение минимального палиндрома

/* Thread 53550, variant 2 */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
 
/********************************************************************/
#define MAX_SIZE    1000
 
 
/********************************************************************/
int calc_minpal( const char *str, int buf_size, char *buf );
 
 
/********************************************************************/
int main( int argc, char *argv[] ) {
 
int buf_size;
char buf[2*MAX_SIZE+1];
 
 
argc--; argv++;
if ( argc != 1 ) {
    fprintf( stderr, "Usage: minpal digit-string\n" );
    exit( 2 );
}
 
buf_size= calc_minpal( argv[0], sizeof(buf), buf );
if ( buf_size<0 ) {
    fprintf( stderr, "Invalid argument\n" );
    exit( 1 );
}
printf( "Original |%s|\n", argv[0] );
printf( "Minpal   |%s|\n", buf );
 
return 0;
 
} /* main() */
 
 
/********************************************************************/
int calc_minpal( const char *str, int buf_size, char *buf ) {
 
int i, j, add, str_size;
int pal_flag;
 
 
/* Check */
str_size= strlen( str );
if ( str_size*2+1>buf_size ) { return -1; }
 
/* Check original */
add= 0;
pal_flag= 1;
for ( i= 0, j= str_size+add-1; i<j; i++, j-- ) {
    if ( str[i] != str[j] ) { pal_flag= 0; break; }
}
if ( pal_flag ) { goto ret_pal; }
 
/* Loop */
for ( add= 1; add<str_size; add++ ) {
 
    /* Check */
    pal_flag= 1;
    for ( i= add, j=str_size-1; i<j; i++, j-- ) {
        if ( str[i] != str[j] ) { pal_flag= 0; break; }
    }
    if ( pal_flag ) { goto ret_pal; }
 
}
 
fprintf( stderr, "Internal error\n" );
return -1;
 
 
/* Create palindrom and return */
ret_pal:
memcpy( buf, str, str_size );
for ( i= 0; i<add; i++ ) { buf[str_size+i]= buf[add-1-i]; }
buf[str_size+add]= '\0';
return str_size+add;
 
} /* calc_minpal() */