Memory access violation after manipulating _m128i pointer.

In my program, i need to manipulate the _m128* POINTER to nevigate through
some memory chunk. Nevigating via POINTER++/-- works absolutely fine; but,
when i try to nevigate this POINTER by more or less than 16 bytes, i get
memory access violation error.

this is how my code looks like:

__m128i *row = (__m128i *)Source; //Source points to an aligned memory
WIDTH_OFFSET = 4; //some non zero number < 16
for(OFFSET = 0; some_condition; OFFSET = WIDTH_OFFSET)
{

row = (__m128i *)((UCHAR*)row - OFFSET) - 1;
*row = _mm_andnot_si128(*row, mmFF);
//mmFF is an initialized _m128i variant

}




here execution is fine in the first entrance of the loop(while OFFSET = 0);
but when i try to increment/decrement the POINTER by (say) 4 bytes, upon next
usage of that POINTER i get a runtime error saying memory access violation.



do help me out with a solution ! thanks.
.

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