[ziyziy89]

compare_block_pointers in the SAS7BCAT catalog reader returns a 64-bit subtraction truncated to int. The values it sorts pack the catalog page number into the high 32 bits ((page << 32) + pos, with page read from the file), so two block pointers on different pages differ only above bit 32 and the truncated result loses that difference. Pointers on pages 1 and 2 compare as equal, and a descending set is left unsorted, so qsort runs with a comparator that violates the required total order (undefined behavior, and out-of-bounds reads in some qsort implementations) and the adjacent-duplicate removal in sas7bcat_uniq_index no longer works, reading and emitting the same catalog block twice.

Compare the two values three-way instead, the same way dta_compare_strls and dta_compare_value_labels already do in this codebase (the latter with a comment about this exact overflow). Reproducer with the current code: compare((1<<32), (2<<32)) returns 0, and qsort of {3<<32, 2<<32, 1<<32} leaves the array in descending order; with the fix it sorts ascending.