parquet_debug_set_perm_rounds Subroutine

public subroutine parquet_debug_set_perm_rounds(n)

Forces the Feistel round count. Test-only. n <= 0 restores the compiled-in value.

Public because it has to be: the value lives in Fortran, and this module reaches no bind(C) surface, so the C++-side debug-hook convention the rest of the library uses is unavailable here. See CLAUDE.md, "A Fortran-side debug hook has to be PUBLIC, so prefer a C++ one".

It is load-bearing rather than convenient, and that is a consequence of the exact path. Every m small enough to enumerate all m! permutations of is also small enough to be answered exactly, so the shipped kernel is uniform by construction at exactly the sizes an exhaustive test can reach -- and an exhaustive test that can only ever confirm a construction proves nothing about the round count. Forcing the count (with parquet_debug_set_perm_force_feistel, which sends those sizes back through the network) is the only way a test can still show that 16 rounds is clean where 4, 8 and 12 are not.

It is excluded from README.md's API overview, no library code calls it, and it has no counterpart in the public contract: pf_random_perm_algorithm names the compiled-in count, and this does not change that string.

Arguments

    subroutine parquet_debug_set_perm_rounds(n)
        integer, intent(in) :: n                    !! rounds to force; `<= 0` restores the default
        if (n <= 0) then
            perm_dbg_rounds = 0
        else
            perm_dbg_rounds = min(n, perm_rounds)
        end if
    end subroutine parquet_debug_set_perm_rounds