Stream-Based Visually Lossless Data Compression Applying Variable Bit-Length ADPCM Encoding

. 2021 Jul 5;21(13):4602. doi: 10.3390/s21134602

Algorithm 1 Encoder of ADPCM [19].

Require:P // a unit of data to be compressed.
Ensure: p // an ADPCM value.

w \leftarrow

W_INIT

P_{p r e v} \leftarrow

P_INIT

C [] \leftarrow [c_{0}, c_{1}, . . ., c_{2^{M - 1}}]

f_{p r e v} \leftarrow w

d \leftarrow P - P_{p r e v}

s t e p \leftarrow (w \times 2) / 2^{M - 1}

d > 0

then
if

| d | / s t e p > 2^{M - 1} - 1

then

p \leftarrow 2^{M - 1} - 1

else

p \leftarrow c e i l (d / s t e p)

end if
else
if

| d | / s t e p > 2^{M} - 1

then

p \leftarrow 2^{M} - 1

else

p \leftarrow c e i l (- d / s t e p) + 2^{M - 1}

end if
end if

f_{p r e v} \leftarrow f_{p r e v} \times C [p & ((1 ≪ M) - 1)] / 64

w \leftarrow f_{p r e v}