Class: ExtSSTRecord

Inherits:
BiffRecord show all
Defined in:
lib/surpass/biff_record.rb

Overview

This record occurs in conjunction with the SST record. It is used by Excel to create a hash table with stream offsets to the SST record to optimise string search operations. Excel may not shorten this record if strings are deleted from the shared string table, so the last part might contain invalid data. The stream indexes in this record divide the SST into portions containing a constant number of strings.

Record EXTSST, BIFF8:

Offset Size Contents 0 2 Number of strings in a portion, this number is >=8 2 var. List of OFFSET structures for all portions. Each OFFSET contains the following data:

Offset Size Contents
0       4   Absolute stream position of first string of the portion
4       2   Position of first string of the portion inside of current record,
            including record header. This counter restarts at zero, if the SST
            record is continued with a CONTINUE record.
6       2   Not used

Constant Summary collapse

RECORD_ID = 
0x00FF

Constants inherited from BiffRecord

BiffRecord::BIFF_LIMIT, BiffRecord::CONTINUE_RECORD_ID

Instance Attribute Summary

Attributes inherited from BiffRecord

#record_data

Instance Method Summary collapse

Methods inherited from BiffRecord

#record_header, #to_biff

Constructor Details

#initialize(sst_stream_pos, str_placement, portions_len) ⇒ ExtSSTRecord

Returns a new instance of ExtSSTRecord.



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# File 'lib/surpass/biff_record.rb', line 1041

def initialize(sst_stream_pos, str_placement, portions_len)
  extsst = {}
  abs_stream_pos = sst_stream_pos
  str_counter = 0
  portion_counter = 0
  
  while (str_counter < str_placement.length) do
    str_chunk_num, pos_in_chunk = str_placement[str_counter]
    if str_chunk_num != portion_counter
      portion_counter = str_chunk_num
      abs_stream_pos += portions_len[portion_counter-1]
    end
    str_stream_pos = abs_stream_pos + pos_in_chunk + 4 # header
    extsst[str_counter] = [pos_in_chunk, str_stream_pos]
    str_counter += 1
  end

  exsst_str_count_delta = [8, str_placement.length*8/0x2000].max
  @record_data = [exsst_str_count_delta].pack('v')
  
  str_counter = 0
  while (str_counter < str_placement.length) do
    @record_data += [extsst[str_counter][1], extsst[str_counter][0], 0].pack('Vvv')
    str_counter += exsst_str_count_delta
  end
end