using memset withing a pure function

[D_Learner via Digitalmars-d-learn]

When writting a pure fucntion involving C non pure functions like 
  memcpy() and   memset() , what could be the way around? Should I 
re-write these and make them pure?


The code am converting is as below :-

int ag_cmatch(const string   pattern, const string text, 
int[char] bmBc ,  int[size] bmGs ) pure {   //Start of AG search 
algorithm		
		int i,j,k , s, shift;
		int[size] skip;
		int[size]  suff;
                 int m = to!int(pattern.length);
                 int n = to!int(text.length);

		int position = -1;

		/* Preprocessing   */

		memset(&skip[0], 0, m* int.sizeof); // Initialise skip table
		
   	 			
		/* searching   */
		j = 0;
		while(j<=n-m){
			i=m-1;
			while( i >= 0){  // Start inner while
				k = skip[i];
				s = suff[i];
				
				if( k > 0)
				if( k > s){
					//writeln(" Int Size 3 ", int.sizeof);
					if(i+1 == s)
						i = (-1);
					else {
						i -=s;
						//writeln("Innner while loop .....Found............... ");
						break;
					}
				}
				else{
					i-=k;
					if( k < s ){
						//	writeln("Innner while loop .....Found<<<<<<  1  
 >>>>>>............... ");
						//getchar();
						break;
					}
				}
				else {
					if ( pattern[i] == text[i+j]){
						--i;
						//writeln("Innner while loop .....Found<<<<<<  2  >>>>>> ");
					}
					else
						break;
				}
			}// End inner while
			
			if ( i< 0){
				//writeln(" AG Pattern found at :", j);
				position = j;//Added for display / reporting
				//getchar();
				
				// Manually added to cause a pattern found stop(Not in 
documentation)
				skip[m-1] = m;
				shift = bmGs[0];
				break;
			}
			else{
				skip[ m-1 ] = m -1 -i;
				shift = bmGs[i] > (bmBc[text[i+j]] - m + 1 + i) ?  bmGs[i]  : 
  (bmBc[text[i+j]] - m + 1 + i )  ;
			}
			
			j+=shift;
			//	writeln(" j Before memcpy== : ", j);
			memcpy(&skip[0], &skip[0]+shift, (m-shift)*(int.sizeof));
			memset(&skip[0]+(m-shift),0, shift*(int.sizeof));
			
		}//End outer while
       return position ;

}//End AG search