latin1prober.rb

######################## BEGIN LICENSE BLOCK ########################
# The Original Code is Mozilla Universal charset detector code.
#
# The Initial Developer of the Original Code is
# Netscape Communications Corporation.
# Portions created by the Initial Developer are Copyright (C) 2001
# the Initial Developer. All Rights Reserved.
#
# Contributor(s):
#   Jeff Hodges - port to Ruby
#   Mark Pilgrim - port to Python
#   Shy Shalom - original C code
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
# 
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.
# 
# You should have received a copy of the GNU Lesser General Public
# License along with this library; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
# 02110-1301  USA
######################### END LICENSE BLOCK #########################

module CharDet
  FREQ_CAT_NUM = 4

  UDF = 0 # undefined
  OTH = 1 # other
  ASC = 2 # ascii capital letter
  ASS = 3 # ascii small letter
  ACV = 4 # accent capital vowel
  ACO = 5 # accent capital other
  ASV = 6 # accent small vowel
  ASO = 7 # accent small other
  CLASS_NUM = 8 # total classes

  Latin1_CharToClass = [
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 00 - 07
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 08 - 0F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 10 - 17
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 18 - 1F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 20 - 27
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 28 - 2F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 30 - 37
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 38 - 3F
    OTH, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 40 - 47
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 48 - 4F
    ASC, ASC, ASC, ASC, ASC, ASC, ASC, ASC,   # 50 - 57
    ASC, ASC, ASC, OTH, OTH, OTH, OTH, OTH,   # 58 - 5F
    OTH, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 60 - 67
    ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 68 - 6F
    ASS, ASS, ASS, ASS, ASS, ASS, ASS, ASS,   # 70 - 77
    ASS, ASS, ASS, OTH, OTH, OTH, OTH, OTH,   # 78 - 7F
    OTH, UDF, OTH, ASO, OTH, OTH, OTH, OTH,   # 80 - 87
    OTH, OTH, ACO, OTH, ACO, UDF, ACO, UDF,   # 88 - 8F
    UDF, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # 90 - 97
    OTH, OTH, ASO, OTH, ASO, UDF, ASO, ACO,   # 98 - 9F
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # A0 - A7
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # A8 - AF
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # B0 - B7
    OTH, OTH, OTH, OTH, OTH, OTH, OTH, OTH,   # B8 - BF
    ACV, ACV, ACV, ACV, ACV, ACV, ACO, ACO,   # C0 - C7
    ACV, ACV, ACV, ACV, ACV, ACV, ACV, ACV,   # C8 - CF
    ACO, ACO, ACV, ACV, ACV, ACV, ACV, OTH,   # D0 - D7
    ACV, ACV, ACV, ACV, ACV, ACO, ACO, ACO,   # D8 - DF
    ASV, ASV, ASV, ASV, ASV, ASV, ASO, ASO,   # E0 - E7
    ASV, ASV, ASV, ASV, ASV, ASV, ASV, ASV,   # E8 - EF
    ASO, ASO, ASV, ASV, ASV, ASV, ASV, OTH,   # F0 - F7
    ASV, ASV, ASV, ASV, ASV, ASO, ASO, ASO,   # F8 - FF
  ]

  # 0 : illegal 
  # 1 : very unlikely 
  # 2 : normal 
  # 3 : very likely
  Latin1ClassModel = [
    # UDF OTH ASC ASS ACV ACO ASV ASO
    0,  0,  0,  0,  0,  0,  0,  0,  # UDF
    0,  3,  3,  3,  3,  3,  3,  3,  # OTH
    0,  3,  3,  3,  3,  3,  3,  3,  # ASC
    0,  3,  3,  3,  1,  1,  3,  3,  # ASS
    0,  3,  3,  3,  1,  2,  1,  2,  # ACV
    0,  3,  3,  3,  3,  3,  3,  3,  # ACO
    0,  3,  1,  3,  1,  1,  1,  3,  # ASV
    0,  3,  1,  3,  1,  1,  3,  3,  # ASO
  ]

  class Latin1Prober < CharSetProber
    def initialize
      super
      reset()
    end

    def reset
      @_mLastCharClass = OTH
      @_mFreqCounter = [0] * FREQ_CAT_NUM
      super
    end

    def get_charset_name
      return "windows-1252"
    end

    def feed(aBuf)
      aBuf = filter_with_english_letters(aBuf)
      aBuf.each_byte do |b|
	c = b.chr
	charClass = Latin1_CharToClass[c[0]]
	freq = Latin1ClassModel[(@_mLastCharClass * CLASS_NUM) + charClass]
	if freq == 0
	  @_mState = ENotMe
	  break
	end
	@_mFreqCounter[freq] += 1
	@_mLastCharClass = charClass
      end

      return get_state()
    end

    def get_confidence
      if get_state() == ENotMe
	return 0.01
      end

      total = @_mFreqCounter.inject{|a,b| a+b} 
      if total < 0.01
	confidence = 0.0
      else
	confidence = (@_mFreqCounter[3] / total) - (@_mFreqCounter[1] * 20.0 / total)
      end
      if confidence < 0.0
	confidence = 0.0
      end
      # lower the confidence of latin1 so that other more accurate detector 
      # can take priority.
      confidence = confidence * 0.5
      return confidence
    end
  end
end