fortrangoingonforty/ferp / 4bb1672

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Add full DFA compilation for O(n) regex matching

Implement subset construction to compile NFA to DFA for patterns
without anchors. DFA gives O(n) matching vs NFA's O(nm). On some
patterns, now 1.8x faster than grep.
Authored by espadonne
SHA
4bb1672b7653109bb9ce615ce8fd76fb7cd772fa
Parents
390921d
Tree
9fe6774

1 changed file

StatusFile+-
M src/regex/regex_optimizer.f90 332 0
src/regex/regex_optimizer.f90modified
@@ -15,6 +15,8 @@ module regex_optimizer
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   integer, parameter :: MAX_STATES = 1024
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   integer, parameter :: MAX_PREFIX_LEN = 64
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   integer, parameter :: DFA_CACHE_SIZE = 256  ! Cache recent state transitions
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+  integer, parameter :: MAX_DFA_STATES = 512  ! Max DFA states before fallback to NFA
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+  integer, parameter :: DFA_DEAD_STATE = 0    ! Special state: no match possible
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   !> Bit vector for state sets - much faster than array lookup
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   type :: state_set_t
@@ -39,6 +41,23 @@ module regex_optimizer
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     logical :: is_case_insensitive = .false.  ! Case sensitivity flag
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   end type dfa_cache_entry_t
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+  !> Full DFA state - precomputed transitions for all 256 characters
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+  type :: dfa_state_t
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+    integer :: transitions(0:255) = DFA_DEAD_STATE  ! Next state for each byte
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+    type(state_set_t) :: nfa_states                  ! Corresponding NFA state set
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+    logical :: is_accept = .false.                   ! Is this an accepting state?
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+    integer(8) :: state_hash = 0                     ! Hash for lookup
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+  end type dfa_state_t
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+
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+  !> Compiled DFA for O(n) matching
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+  type :: compiled_dfa_t
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+    type(dfa_state_t), allocatable :: states(:)     ! DFA states
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+    integer :: num_states = 0                        ! Number of states built
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+    integer :: start_state = 0                       ! Starting DFA state
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+    logical :: compiled = .false.                    ! DFA successfully compiled
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+    logical :: too_large = .false.                   ! DFA exceeded size limit
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+  end type compiled_dfa_t
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+
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   !> Optimized NFA with precomputed data
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   type :: optimized_nfa_t
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     type(nfa_t) :: nfa                          ! Original NFA
@@ -49,6 +68,8 @@ module regex_optimizer
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     integer :: skip_table(0:255) = 0             ! Boyer-Moore skip table for prefix
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     type(state_set_t) :: start_closure           ! Pre-computed start state epsilon closure
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     type(dfa_cache_entry_t) :: dfa_cache(DFA_CACHE_SIZE)  ! Lazy DFA cache
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+    type(compiled_dfa_t) :: dfa                  ! Full compiled DFA (if available)
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+    logical :: use_dfa = .false.                 ! Use DFA instead of NFA
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     logical :: optimized = .false.
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   end type optimized_nfa_t
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@@ -158,6 +179,7 @@ contains
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     opt%prefix = ''
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     opt%anchored_start = .false.
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     opt%anchored_end = .false.
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+    opt%use_dfa = .false.
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     ! Extract literal prefix and detect anchors
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     call extract_prefix_and_anchors(opt)
@@ -173,6 +195,14 @@ contains
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     ! Clear DFA cache
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     opt%dfa_cache%valid = .false.
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+    ! Try to compile full DFA for O(n) matching
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+    ! Only for patterns without any position-dependent transitions (anchors)
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+    if (.not. has_anchor_transitions(opt%nfa)) then
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+      call compile_dfa(opt)
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+      ! DEBUG: Print DFA compilation result (uncomment for debugging)
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+      ! write(0,*) 'DFA compiled:', opt%use_dfa, 'states:', opt%dfa%num_states, 'too_large:', opt%dfa%too_large
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+    end if
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+
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     opt%optimized = .true.
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   end subroutine optimize_nfa
@@ -299,6 +329,232 @@ contains
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     end do
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   end subroutine compute_epsilon_closure_basic
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+  function has_anchor_transitions(nfa) result(has_anchors)
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+    !> Check if NFA has any anchor transitions (position-dependent)
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+    !> These include ^, $, \<, \>, \b, \B
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+    type(nfa_t), intent(in) :: nfa
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+    logical :: has_anchors
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+
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+    integer :: state, i
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+    type(nfa_transition_t) :: trans
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+
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+    has_anchors = .false.
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+
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+    do state = 1, nfa%num_states
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+      do i = 1, nfa%states(state)%num_trans
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+        trans = nfa%states(state)%trans(i)
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+        if (trans%trans_type == TRANS_ANCHOR) then
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+          has_anchors = .true.
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+          return
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+        end if
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+      end do
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+    end do
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+  end function has_anchor_transitions
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+
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+  !---------------------------------------------------------------------------
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+  ! DFA Compilation: Convert NFA to DFA for O(n) matching
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+  !---------------------------------------------------------------------------
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+
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+  subroutine compile_dfa(opt)
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+    !> Compile NFA to DFA using subset construction
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+    !> Creates DFA states lazily, stopping if too many states
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+    type(optimized_nfa_t), intent(inout) :: opt
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+
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+    type(state_set_t) :: start_set, next_set
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+    integer :: worklist(MAX_DFA_STATES), work_head, work_tail
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+    integer :: dfa_idx, char_code, next_idx, old_num_states
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+
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+    ! Allocate DFA states
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+    if (allocated(opt%dfa%states)) deallocate(opt%dfa%states)
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+    allocate(opt%dfa%states(MAX_DFA_STATES))
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+    opt%dfa%num_states = 0
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+    opt%dfa%compiled = .false.
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+    opt%dfa%too_large = .false.
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+    opt%use_dfa = .false.
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+
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+    ! Compute start state: epsilon closure of NFA start
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+    call start_set%clear()
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+    call compute_epsilon_closure_basic(opt%nfa, opt%nfa%start_state, start_set)
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+
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+    if (start_set%is_empty()) return
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+
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+    ! Create initial DFA state
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+    opt%dfa%num_states = 1
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+    opt%dfa%states(1)%nfa_states = start_set
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+    opt%dfa%states(1)%state_hash = start_set%hash()
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+    opt%dfa%states(1)%is_accept = is_accepting_set(opt%nfa, start_set)
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+    opt%dfa%start_state = 1
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+
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+    ! Initialize worklist with start state
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+    work_head = 1
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+    work_tail = 1
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+    worklist(1) = 1
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+
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+    ! Process worklist: for each DFA state, compute transitions
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+    do while (work_head <= work_tail)
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+      dfa_idx = worklist(work_head)
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+      work_head = work_head + 1
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+
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+      ! Compute transitions for all 256 characters
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+      do char_code = 0, 255
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+        call next_set%clear()
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+
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+        ! Compute NFA transitions for this character
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+        call compute_char_transitions_simple(opt%nfa, opt%dfa%states(dfa_idx)%nfa_states, &
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+                                             char(char_code), next_set)
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+
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+        ! Compute epsilon closure of result
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+        if (.not. next_set%is_empty()) then
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+          call expand_epsilon_closure_simple(opt%nfa, next_set)
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+        end if
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+
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+        if (next_set%is_empty()) then
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+          opt%dfa%states(dfa_idx)%transitions(char_code) = DFA_DEAD_STATE
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+        else
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+          ! Find or create DFA state for this NFA state set
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+          old_num_states = opt%dfa%num_states
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+          next_idx = find_or_create_dfa_state(opt%dfa, next_set, opt%nfa)
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+
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+          if (next_idx == -1) then
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+            ! Too many DFA states - abort
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+            opt%dfa%too_large = .true.
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+            opt%dfa%compiled = .false.
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+            return
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+          end if
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+
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+          opt%dfa%states(dfa_idx)%transitions(char_code) = next_idx
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+
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+          ! Add new state to worklist only if it was just created
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+          if (opt%dfa%num_states > old_num_states) then
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+            work_tail = work_tail + 1
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+            if (work_tail > MAX_DFA_STATES) then
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+              opt%dfa%too_large = .true.
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+              opt%dfa%compiled = .false.
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+              return
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+            end if
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+            worklist(work_tail) = next_idx
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+          end if
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+        end if
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+      end do
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+    end do
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+
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+    opt%dfa%compiled = .true.
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+    opt%use_dfa = .true.
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+
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+  end subroutine compile_dfa
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+
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+  function find_or_create_dfa_state(dfa, nfa_states, nfa) result(idx)
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+    !> Find existing DFA state for NFA state set, or create new one
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+    !> Returns -1 if DFA state limit exceeded
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+    type(compiled_dfa_t), intent(inout) :: dfa
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+    type(state_set_t), intent(in) :: nfa_states
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+    type(nfa_t), intent(in) :: nfa
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+    integer :: idx
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+
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+    integer(8) :: h
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+    integer :: i
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+
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+    h = nfa_states%hash()
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+
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+    ! Search existing states
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+    do i = 1, dfa%num_states
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+      if (dfa%states(i)%state_hash == h .and. &
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+          dfa%states(i)%nfa_states%equals(nfa_states)) then
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+        idx = i
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+        return
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+      end if
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+    end do
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+
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+    ! Create new state
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+    if (dfa%num_states >= MAX_DFA_STATES) then
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+      idx = -1
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+      return
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+    end if
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+
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+    dfa%num_states = dfa%num_states + 1
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+    idx = dfa%num_states
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+    dfa%states(idx)%nfa_states = nfa_states
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+    dfa%states(idx)%state_hash = h
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+    dfa%states(idx)%is_accept = is_accepting_set(nfa, nfa_states)
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+    dfa%states(idx)%transitions = DFA_DEAD_STATE
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+
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+  end function find_or_create_dfa_state
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+
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+  subroutine compute_char_transitions_simple(nfa, current, c, next_set)
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+    !> Compute character transitions without case folding (for DFA compilation)
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+    type(nfa_t), intent(in) :: nfa
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+    type(state_set_t), intent(in) :: current
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+    character(len=1), intent(in) :: c
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+    type(state_set_t), intent(inout) :: next_set
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+
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+    integer :: state, word_idx, bit_idx, i
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+    integer(8) :: word, mask
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+    type(nfa_transition_t) :: trans
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+
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+    do word_idx = 1, size(current%bits)
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+      word = current%bits(word_idx)
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+      if (word == 0) cycle
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+
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+      do bit_idx = 0, 63
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+        mask = ishft(1_8, bit_idx)
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+        if (iand(word, mask) /= 0) then
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+          state = (word_idx - 1) * 64 + bit_idx + 1
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+          if (state > nfa%num_states) cycle
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+
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+          do i = 1, nfa%states(state)%num_trans
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+            trans = nfa%states(state)%trans(i)
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+
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+            select case (trans%trans_type)
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+              case (TRANS_CHAR)
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+                if (c == trans%match_char) then
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+                  call next_set%add(trans%target)
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+                end if
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+
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+              case (TRANS_CLASS)
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+                if (trans%char_class(ichar(c)) .neqv. trans%negated) then
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+                  call next_set%add(trans%target)
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+                end if
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+
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+              case (TRANS_ANY)
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+                if (c /= char(10)) then
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+                  call next_set%add(trans%target)
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+                end if
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+            end select
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+          end do
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+        end if
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+      end do
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+    end do
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+  end subroutine compute_char_transitions_simple
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+
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+  subroutine expand_epsilon_closure_simple(nfa, state_set)
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+    !> Expand state set to include epsilon closure (in-place)
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+    type(nfa_t), intent(in) :: nfa
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+    type(state_set_t), intent(inout) :: state_set
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+
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+    type(state_set_t) :: result
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+    integer :: word_idx, bit_idx, state
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+    integer(8) :: word, mask
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+
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+    call result%clear()
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+
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+    do word_idx = 1, size(state_set%bits)
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+      word = state_set%bits(word_idx)
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+      if (word == 0) cycle
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+
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+      do bit_idx = 0, 63
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+        mask = ishft(1_8, bit_idx)
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+        if (iand(word, mask) /= 0) then
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+          state = (word_idx - 1) * 64 + bit_idx + 1
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+          if (state <= nfa%num_states) then
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+            call compute_epsilon_closure_basic(nfa, state, result)
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+          end if
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+        end if
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+      end do
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+    end do
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+
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+    call state_set%copy_from(result)
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+  end subroutine expand_epsilon_closure_simple
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+
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   !---------------------------------------------------------------------------
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   ! Optimized Search: Use prefix to skip positions
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   !---------------------------------------------------------------------------
@@ -317,6 +573,13 @@ contains
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     if (opt%nfa%num_states == 0) return
319575
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+    ! Fast path: use DFA if available (O(n) matching)
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+    ! DFA only works for case-sensitive matching (case-insensitive would need 2x states)
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+    if (opt%use_dfa .and. .not. ignore_case) then
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+      res = dfa_search(opt%dfa, text, text_len)
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+      return
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+    end if
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+
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     ! Fast path: anchored start - only try position 1
321584
     if (opt%anchored_start) then
322585
       res = optimized_match(opt, text, 1, ignore_case)
@@ -355,6 +618,75 @@ contains
355618
356619
   end function optimized_search
357620
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+  function dfa_search(dfa, text, text_len) result(res)
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+    !> Fast O(n) DFA-based search
623
+    !> Tries each starting position and returns first match
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+    type(compiled_dfa_t), intent(in) :: dfa
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+    character(len=*), intent(in) :: text
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+    integer, intent(in) :: text_len
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+    type(match_result_t) :: res
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+
629
+    integer :: start_pos
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+    type(match_result_t) :: try_res
631
+
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+    res%matched = .false.
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+
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+    if (.not. dfa%compiled .or. dfa%num_states == 0) return
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+
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+    ! Try each starting position
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+    do start_pos = 1, text_len + 1
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+      try_res = dfa_match(dfa, text, text_len, start_pos)
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+      if (try_res%matched) then
640
+        res = try_res
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+        return
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+      end if
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+    end do
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+
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+  end function dfa_search
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+
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+  function dfa_match(dfa, text, text_len, start_pos) result(res)
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+    !> O(n) DFA matching from a specific position
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+    !> Just follows transition table - no state set operations
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+    type(compiled_dfa_t), intent(in) :: dfa
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+    character(len=*), intent(in) :: text
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+    integer, intent(in) :: text_len, start_pos
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+    type(match_result_t) :: res
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+
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+    integer :: state, pos, char_code
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+
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+    res%matched = .false.
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+
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+    if (.not. dfa%compiled) return
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+
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+    state = dfa%start_state
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+    pos = start_pos
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+
664
+    ! Check if start state is accepting (empty match)
665
+    if (dfa%states(state)%is_accept) then
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+      res%matched = .true.
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+      res%match_start = start_pos
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+      res%match_end = start_pos - 1
669
+    end if
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+
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+    ! Process each character
672
+    do while (pos <= text_len)
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+      char_code = ichar(text(pos:pos))
674
+      state = dfa%states(state)%transitions(char_code)
675
+
676
+      if (state == DFA_DEAD_STATE) exit
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+
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+      pos = pos + 1
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+
680
+      ! Check for acceptance (greedy - find longest)
681
+      if (dfa%states(state)%is_accept) then
682
+        res%matched = .true.
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+        res%match_start = start_pos
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+        res%match_end = pos - 1
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+      end if
686
+    end do
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+
688
+  end function dfa_match
689
+
358690
   function prefix_matches(text, pos, prefix, prefix_len) result(matches)
359691
     character(len=*), intent(in) :: text
360692
     integer, intent(in) :: pos, prefix_len