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latin1prober.py
######################## 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):
#   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 #########################

from charsetprober import CharSetProber
import constants
import operator

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
)

00096 class Latin1Prober(CharSetProber):
    def __init__(self):
        CharSetProber.__init__(self)
        self.reset()

    def reset(self):
        self._mLastCharClass = OTH
        self._mFreqCounter = [0] * FREQ_CAT_NUM
        CharSetProber.reset(self)

    def get_charset_name(self):
        return "windows-1252"

    def feed(self, aBuf):
        aBuf = self.filter_with_english_letters(aBuf)
        for c in aBuf:
            charClass = Latin1_CharToClass[ord(c)]
            freq = Latin1ClassModel[(self._mLastCharClass * CLASS_NUM) + charClass]
            if freq == 0:
                self._mState = constants.eNotMe
                break
            self._mFreqCounter[freq] += 1
            self._mLastCharClass = charClass

        return self.get_state()

    def get_confidence(self):
        if self.get_state() == constants.eNotMe:
            return 0.01
  
        total = reduce(operator.add, self._mFreqCounter)
        if total < 0.01:
            confidence = 0.0
        else:
            confidence = (self._mFreqCounter[3] / total) - (self._mFreqCounter[1] * 20.0 / total)
        if confidence < 0.0:
            confidence = 0.0
        # lower the confidence of latin1 so that other more accurate detector 
        # can take priority.
        confidence = confidence * 0.5
        return confidence

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