Merge branch 'briandobbins/compare_offsets_fix' (PR #631)

Fix overflow/underflow issues during qsort for the SUBSET
rearranger.

The comparator function given to the qsort call in the rearranger
returns a 32-bit integer, but the operands can be 64-bit. Depending
on the difference in value, you can get an overflow or underflow,
which means you read an incorrect amount of data.

* briandobbins/compare_offsets_fix:
  Fixes integer under/overflow issue when casting 64-bit offsets to 32-bit qsort comparator return value

Author: jayeshkrishna

src/clib/pio_rearrange.cpp

@@ -1964,7 +1964,10 @@ int compare_offsets(const void *a, const void *b)
     mapsort *y = (mapsort *)b;
     if (!x || !y)
         return 0;
-    return (int)(x->iomap - y->iomap);
+
+    if (x->iomap < y->iomap) { return -1; }
+    if (x->iomap > y->iomap) { return 1; }
+    return 0;
 }
 
 /**