remove gcc ternary if extension ok stsp@

set diff box recursion limit to UINT_MAX by default In practice, recursion is already limited by our Myers max-effort cut and this heuristic should generally provide a better split than a limit on the number of diff boxes. A recursion limit is only required for diff configs that do not include the Myers algorithm, which we currently don't have. Discussed with Neels

fix result chunks: add minus above plus failed to shift "empty" positions

undup code to add result chunks

add sanity assertions around adding result chunks uncovers errors related to placing minus chunks above already added plus chunks.

patience debug

debug fix in diff_data_init_subsection

debug init subsection

allow diff API users to atomize files separately This is a breaking API change (not that we care about that at this point). This can avoid redundant work spent on atomizing a file multiple times. There are use cases where one particular file must be compared to other files over and over again, such as when blaming file history. The old API gave access to both versions of the file to the atomizer just in case a future atomizer implementation needs this. This can still be achieved by passing a second file via the atomizer's private data pointer.

optimize diff_atom_same(): if hashes differ, return false

diff_atom_cmp: no special case for ignore whitespace when both atoms empty

cache kd_buf in struct diff_state to avoid repeated allocation + free

initialize to NULL instead of ""; allows pointer check to see if file is mapped

rename diff_atom->d to diff_atom->root, because it always is The idea was that for each diff box within the files, the atoms would have a backpointer to the current layer of diff_data (indicating the current section), but it is not actually needed to update the backpointer in each atom to the current diff_data. That is why the current code always points atom->d to the root diff_data for the entire file. Clarify by proper name. Constructs like atom->d->root->foo are redundant, just use atom->root->foo.

diff_main: don't run algo if left or right are empty

debug: fix logging first chunk

diff_algo_none: cosmetics

fix diff_algo_none() for ending in plus chunk

results: also combine chunks coming from temp_chunks

fix diff_algo_none(): no NULL pointers for left_start and right_start

diff_state_add_chunk(): fix adding minus above plus chunk: wrong idx

debug tweaks for diff_state_add_chunk()

diff_algo_none(): also detect equal lines at the end

cosmetic: diff_algo_none(): rename to equal_lines_start

cosmetic: diff_algo_none: local pointers for shorter code