Module: Wexpr::UVLQ64

Defined in:
lib/wexpr/uvlq64.rb

Overview

Helpers for managing VLQ 64bit binary

Class Method Summary collapse

Class Method Details

.byte_size(value) ⇒ Object

Return the number of bytes which is needed to store a number in the UVLQ64



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# File 'lib/wexpr/uvlq64.rb', line 10

def self.byte_size(value)
  # we get 7 bits per byte. 2^7 for each.
  case value
    when 0 ... 128 then return 1 # 2^7
    when 128 ... 16384 then return 2 # 2^14
    when 16384 ... 2097152 then return 3 # 2^21
    when 2097152 ... 268435456 then return 4 # 2^28
    when 268435456 ... 34359738368 then return 5 # 2^35
    when 34359738368 ... 4398046511104 then return 6 # 2^42
    when 4398046511104 ... 562949953421312 then return 7 # 2^49
    when 562949953421312 ... 72057594037927936 then return 8 # 2^56
    when 72057594037927936 ... 9223372036854775808 then return 9 # 2^63
    else
      return 10 # 2^64+
  end
end

.read(buffer) ⇒ Object

Read a UVLQ64 big endian from the given buffer. binary -> value Returns the result along with the rest of the buffer not processed



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# File 'lib/wexpr/uvlq64.rb', line 49

def self.read(buffer)
  r = 0
  bufferPos = 0
  bufferLen = buffer.size
  
  loop do
    if bufferPos == bufferLen
      raise StandardError("Ran out of buffer processing UVLQ64")
    end
    
    c = buffer[bufferPos].unpack('C')[0]
    r = (r << 7) | (c & 127)
    
    isEnd = (c & 128) == 0
    bufferPos += 1
    break if isEnd
  end
  
  return r, buffer[bufferPos..-1]
end

.write(value) ⇒ Object

Write a UVLQ64 (big endian) to a buffer. value -> binary.



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# File 'lib/wexpr/uvlq64.rb', line 30

def self.write(value)
  bytesNeeded = byte_size(value)
  
  buf = []
  
  i = bytesNeeded - 1
  for j in 0 .. i
    buf << (((value >> ((i - j) * 7)) & 127) | 128)
  end
  
  buf[i] ^= 128
  
  return buf.pack('C*')
end