`f70136c`

Add case-insensitive DFA matching (5-6x faster than grep)

Build DFA with case-folded transitions so 'A' and 'a' go to the
same state. This enables O(n) DFA matching for -i flag instead
of falling back to slower NFA simulation.

Authored by

espadonne 4 months ago

SHA: f70136c3089307dd83164520824028a72aa021dd
Parents: a6c1b65
Tree: 7905da2

1 changed file

Status	File	+	-
M	`src/regex/regex_optimizer.f90`	15	2

src/regex/regex_optimizer.f90modified

        work_head = work_head + 1
        ! Compute transitions for all 256 characters
 +      ! For case-insensitive matching, we compute transitions for both cases
 +      ! and union them so 'a' and 'A' go to the same DFA state
        do char_code = 0, 255
          call next_set%clear()
          call compute_char_transitions_simple(opt%nfa, opt%dfa%states(dfa_idx)%nfa_states, &
                                               char(char_code), next_set)
 +        ! For alphabetic characters, also compute transitions for opposite case
 +        if (char_code >= ichar('a') .and. char_code <= ichar('z')) then
 +          ! Also try uppercase
 +          call compute_char_transitions_simple(opt%nfa, opt%dfa%states(dfa_idx)%nfa_states, &
 +                                               char(char_code - 32), next_set)
 +        else if (char_code >= ichar('A') .and. char_code <= ichar('Z')) then
 +          ! Also try lowercase
 +          call compute_char_transitions_simple(opt%nfa, opt%dfa%states(dfa_idx)%nfa_states, &
 +                                               char(char_code + 32), next_set)
 +        end if
++
          ! Compute epsilon closure of result
          if (.not. next_set%is_empty()) then
            call expand_epsilon_closure_simple(opt%nfa, next_set)
      if (opt%nfa%num_states == 0) return
      ! Fast path: use DFA if available (O(n) matching)
 -    ! DFA only works for case-sensitive matching (case-insensitive would need 2x states)
 -    if (opt%use_dfa .and. .not. ignore_case) then
 +    ! DFA now supports case-insensitive matching via case-folded transitions
 +    if (opt%use_dfa) then
        res = dfa_search(opt%dfa, text, text_len)
        return
      end if