An Adaptive Lossless Data Compression Scheme for Wireless Sensor Networks

Algorithm 3

Pseudo-code of the encode () function.

encode( d_i , TABLE, c_i )

// 𝑑_𝑖 is the current residue value

// TABLE is the variable length Huffman codes used in encoding

// 𝑏_𝑖 is the category (group number) of 𝑑_𝑖

// 𝑏_𝑖 is also the number of lower order bits needed to encode the value of 𝑑_𝑖

// 𝑐_𝑖 is the encoded bitstream of 𝑑_𝑖

// ℎ_𝑖 is the variable-length Huffman code that codifies the category (group) of 𝑑_𝑖

// 𝑙_𝑖 is the variable-length integer code that codifies the index position of 𝑑_𝑖

// within its group (category)

// *denotes concatenation

// (Index)∣𝑏_𝑖 denotes the binary representation of index over 𝑏_𝑖 bits

// compute 𝑑_𝑖 category

IF 𝑑_𝑖=0 THEN

 SET 𝑏_𝑖 TO 0

ELSE

 SET 𝑏_𝑖 TO ⌈log₂(|𝑑_𝑖|)⌉

ENDIF

// extract ℎ_𝑖 the variable length Huffman code from TABLE

SET ℎ_𝑖 TO TABLE [𝑏_𝑖]

// build 𝑐_𝑖

IF 𝑏_𝑖=0 THEN

 // 𝑙_𝑖 is not needed

 SET 𝑐_𝑖 TO ℎ_𝑖

ELSE

 // build 𝑙_𝑖

 SET 𝑙_𝑖 TO (Index)∣𝑏_𝑖

 // build 𝑐_𝑖

 SET 𝑐_𝑖 TO ℎ_𝑖 * 𝑙_𝑖

ENDIF

RETURN 𝑐_𝑖