ADPCM stands for Adaptive Differential Pulse Code Modulation, and it’s a compression technique used to reduce data transmission costs by encoding only the differences between consecutive values instead of transmitting every single value separately. This can be especially useful in stateless protocols where there is no state information being transmitted or maintained on either end.
So let’s say you have two devices, one sending and one receiving data over a stateless connection. The sender generates some data, encodes it using ADPCM, and sends the compressed data to the receiver. The receiver then decodes the received data and displays it on its screen or uses it for further processing.
Here’s how you can implement ADPCM in your code:
1. First, let’s create a function that encodes our input data using ADPCM. We’ll use Python as an example language, but this technique is applicable to other languages too.
# Function to encode data using ADPCM
def adpcm_encode(data):
# Initialize variables for encoding and decoding
prev = 0 # variable to store previous value
step1 = 7680 # first step size for encoding
step2 = 1920 # second step size for encoding
step3 = 456 # third step size for encoding
step4 = 128 # fourth step size for encoding
encoded_data = [] # list to store encoded data
for value in data:
# Calculate the difference between current and previous values
diff = value - prev # corrected syntax for calculating difference
# Encode the difference using ADPCM
if abs(diff) > step1:
sign = 0 if diff >= 0 else 256 # determine sign of difference
encoded_value = (abs(diff) // step1) * step4 + sign # corrected syntax for encoding
elif abs(diff) > step2:
sign = 0 if diff >= 0 else 256 # determine sign of difference
encoded_value = ((abs(diff) // step2) * step4) + (sign | 192) # corrected syntax for encoding
else:
encoded_value = abs(diff) // step4 * step4 # corrected syntax for encoding
# Store the encoded value and update previous for next iteration
prev = value # update previous value
encoded_data.append(encoded_value & 0xFF) # append encoded value to list
return bytes(encoded_data) # return encoded data as bytes
2. Next, let’s create a function that decodes our input data using ADPCM. This is the reverse of the encoding process: we decode each compressed value and calculate its original value based on the previous value and the encoded difference.
# Function to decode input data using ADPCM
def adpcm_decode(data):
# Initialize variables for encoding and decoding
prev = 0 # variable to store previous value
step1 = 7680 # step size for first range of encoded values
step2 = 1920 # step size for second range of encoded values
step3 = 456 # step size for third range of encoded values
step4 = 128 # step size for fourth range of encoded values
decoded_data = [] # list to store decoded values
for encoded_value in data: # loop through each encoded value in input data
# Calculate the difference between current and previous values using ADPCM
sign = (encoded_value & 192) >> 6 # extract sign bit from encoded value
if encoded_value < step4 * 16: # check if encoded value falls within first range
diff = encoded_value // step4 * step4 # calculate difference using first step size
elif encoded_value >= (step3 << 8) + (sign | 192): # check if encoded value falls within second range
diff = ((encoded_value & ~(192 | sign)) << 8) // step3 * step4 # calculate difference using second step size
else: # encoded value falls within third range
diff = ((encoded_value & ~(192 | sign)) << 8 + (sign | 192)) // step2 * step4 # calculate difference using third step size
# Update previous value for next iteration and store the decoded value
prev += diff # add difference to previous value
decoded_data.append(prev) # append decoded value to list
return bytes(decoded_data) # return decoded data as bytes
And that’s it! You can now use these functions to encode and decode data using ADPCM in your stateless protocols, reducing the amount of data transmitted over the connection while maintaining a high level of accuracy.
So next time you find yourself lost in a stateless mess, remember: just ADPCM your way out!