Cython/Plex/Transitions.py

#
# Plex - Transition Maps
#
# This version represents state sets directly as dicts for speed.
#

from __future__ import absolute_import

try:
    from sys import maxsize as maxint
except ImportError:
    from sys import maxint


class TransitionMap(object):
    """
    A TransitionMap maps an input event to a set of states.
    An input event is one of: a range of character codes,
    the empty string (representing an epsilon move), or one
    of the special symbols BOL, EOL, EOF.

    For characters, this implementation compactly represents
    the map by means of a list:

      [code_0, states_0, code_1, states_1, code_2, states_2,
        ..., code_n-1, states_n-1, code_n]

    where |code_i| is a character code, and |states_i| is a
    set of states corresponding to characters with codes |c|
    in the range |code_i| <= |c| <= |code_i+1|.

    The following invariants hold:
      n >= 1
      code_0 == -maxint
      code_n == maxint
      code_i < code_i+1 for i in 0..n-1
      states_0 == states_n-1

    Mappings for the special events '', BOL, EOL, EOF are
    kept separately in a dictionary.
    """

    map = None      # The list of codes and states
    special = None  # Mapping for special events

    def __init__(self, map=None, special=None):
        if not map:
            map = [-maxint, {}, maxint]
        if not special:
            special = {}
        self.map = map
        self.special = special
        #self.check() ###

    def add(self, event, new_state,
            TupleType=tuple):
        """
        Add transition to |new_state| on |event|.
        """
        if type(event) is TupleType:
            code0, code1 = event
            i = self.split(code0)
            j = self.split(code1)
            map = self.map
            while i < j:
                map[i + 1][new_state] = 1
                i += 2
        else:
            self.get_special(event)[new_state] = 1

    def add_set(self, event, new_set,
                TupleType=tuple):
        """
        Add transitions to the states in |new_set| on |event|.
        """
        if type(event) is TupleType:
            code0, code1 = event
            i = self.split(code0)
            j = self.split(code1)
            map = self.map
            while i < j:
                map[i + 1].update(new_set)
                i += 2
        else:
            self.get_special(event).update(new_set)

    def get_epsilon(self,
                    none=None):
        """
        Return the mapping for epsilon, or None.
        """
        return self.special.get('', none)

    def iteritems(self,
                  len=len):
        """
        Return the mapping as an iterable of ((code1, code2), state_set) and
        (special_event, state_set) pairs.
        """
        result = []
        map = self.map
        else_set = map[1]
        i = 0
        n = len(map) - 1
        code0 = map[0]
        while i < n:
            set = map[i + 1]
            code1 = map[i + 2]
            if set or else_set:
                result.append(((code0, code1), set))
            code0 = code1
            i += 2
        for event, set in self.special.items():
            if set:
                result.append((event, set))
        return iter(result)

    items = iteritems

    # ------------------- Private methods --------------------

    def split(self, code,
              len=len, maxint=maxint):
        """
        Search the list for the position of the split point for |code|,
        inserting a new split point if necessary. Returns index |i| such
        that |code| == |map[i]|.
        """
        # We use a funky variation on binary search.
        map = self.map
        hi = len(map) - 1
        # Special case: code == map[-1]
        if code == maxint:
            return hi
        # General case
        lo = 0
        # loop invariant: map[lo] <= code < map[hi] and hi - lo >= 2
        while hi - lo >= 4:
            # Find midpoint truncated to even index
            mid = ((lo + hi) // 2) & ~1
            if code < map[mid]:
                hi = mid
            else:
                lo = mid
        # map[lo] <= code < map[hi] and hi - lo == 2
        if map[lo] == code:
            return lo
        else:
            map[hi:hi] = [code, map[hi - 1].copy()]
            #self.check() ###
            return hi

    def get_special(self, event):
        """
        Get state set for special event, adding a new entry if necessary.
        """
        special = self.special
        set = special.get(event, None)
        if not set:
            set = {}
            special[event] = set
        return set

    # --------------------- Conversion methods -----------------------

    def __str__(self):
        map_strs = []
        map = self.map
        n = len(map)
        i = 0
        while i < n:
            code = map[i]
            if code == -maxint:
                code_str = "-inf"
            elif code == maxint:
                code_str = "inf"
            else:
                code_str = str(code)
            map_strs.append(code_str)
            i += 1
            if i < n:
                map_strs.append(state_set_str(map[i]))
            i += 1
        special_strs = {}
        for event, set in self.special.items():
            special_strs[event] = state_set_str(set)
        return "[%s]+%s" % (
            ','.join(map_strs),
            special_strs
        )

    # --------------------- Debugging methods -----------------------

    def check(self):
        """Check data structure integrity."""
        if not self.map[-3] < self.map[-1]:
            print(self)
            assert 0

    def dump(self, file):
        map = self.map
        i = 0
        n = len(map) - 1
        while i < n:
            self.dump_range(map[i], map[i + 2], map[i + 1], file)
            i += 2
        for event, set in self.special.items():
            if set:
                if not event:
                    event = 'empty'
                self.dump_trans(event, set, file)

    def dump_range(self, code0, code1, set, file):
        if set:
            if code0 == -maxint:
                if code1 == maxint:
                    k = "any"
                else:
                    k = "< %s" % self.dump_char(code1)
            elif code1 == maxint:
                k = "> %s" % self.dump_char(code0 - 1)
            elif code0 == code1 - 1:
                k = self.dump_char(code0)
            else:
                k = "%s..%s" % (self.dump_char(code0),
                                self.dump_char(code1 - 1))
            self.dump_trans(k, set, file)

    def dump_char(self, code):
        if 0 <= code <= 255:
            return repr(chr(code))
        else:
            return "chr(%d)" % code

    def dump_trans(self, key, set, file):
        file.write("      %s --> %s\n" % (key, self.dump_set(set)))

    def dump_set(self, set):
        return state_set_str(set)


#
#   State set manipulation functions
#

#def merge_state_sets(set1, set2):
#        for state in set2.keys():
#            set1[state] = 1

def state_set_str(set):
    return "[%s]" % ','.join(["S%d" % state.number for state in set])