Php > Algorithms

This function returns the position of string s1 within string s2

This function returns the position of string s1 within string s2
The position is 1 based. If s1 is not in s2, 0 is returned

<?php 
/*  This  function  returns  the  position  of  string  s1  within  string  s2. 
      The  position  is  1  based.    If  s1  is  not  in  s2,  0  is  returned. 
*/ 
function  InStr($s1,  $s2) 
{ 
        //Check  for  valid  input 
        if(!(is_string($s1)  &&  is_string($s2)))  return  0; 

        $s1len  =  strlen($s1); 
        $s2len  =  strlen($s2); 

        //Check  if  s1  in  s2  at  all 
        if(!ereg($s1,  $s2))  return  0; 

        //Resolve  simple  case 
        if($s1  ==  $s2)  return  1; 

        //Set  initial  search  limits 
        $begin  =  0; 
        $end  =  $s2len  -  $s1len; 

        //Initialize  position 
        $position  =  0; 

        //Do  binary  search  of  s2  for  s1 
        //Check  left  side  first  to  find  first  occurance  of  s1 
        //Check  right  side  first  to  find  last  occurance  of  s1 
        while($end  >  $begin  +  1) 
        { 
                $middle  =  ceil(($begin  +  $end)  /  2); 
                $leftBegin  =  $begin; 
                $rightBegin  =  $middle  +  $s1len; 
                $leftEnd  =  $middle; 
                $rightEnd  =  $end  +  $s1len; 

                //Check  left  first 
                if(ereg($s1,  substr($s2,  $leftBegin,  $rightBegin  -  $leftBegin))) 
                { 
                        $end  =  $middle; 
                } 
                else  //(ereg($s1,  substr($s2,  $leftEnd,  $rightEnd  -  $leftEnd))) 
                { 
                        $position  +=  $middle  -  $begin; 
                        $begin  =  $middle; 
                } 
        } 

        //Resolve  1  off  problems  introduced  by  ceil 
        if(ereg($s1,  substr($s2,  $end,  $s1len)))  $position++; 

        //Return  position  1  based 
        return  $position  +  1; 
} 
?>