Create a C Version of Adler32

How Can I Generate a C Function for Adler32?

You can use GitHub Copilot to generate a simple C version of the Adler32 checksum algorithm.

On your Arm Linux computer, create a new directory and enter the empty directory:

    

        
        
mkdir adler32 && cd adler32

    

Open VS Code in the new directory to start the project:

    

        
        
code . &

    

Open GitHub Copilot, select the Large Language Model (LLM) you want to use, and select Agent mode.

Copy and paste the information below as a GitHub Copilot prompt and click the Send button.

    

        
        
Write a basic C implementation of the adler32 checksum function. 
Write the function in a file named adler32-simple.c that can be called from another C file. 
Don't create a C main function yet.

    

The output is:

    

        
        
GitHub Copilot: I'll create a basic C implementation of the Adler-32 checksum function in a file named adler32-simple.c. Let me do that for you.

First, let me check if the file exists already:The file doesn't exist yet, so I'll create it. Let me write the Adler-32 checksum implementation for you.

The Adler-32 checksum algorithm works by calculating two 16-bit checksums A and B and combining them into a single 32-bit checksum. It's a simple algorithm that provides decent error detection with minimal computational overhead.

/*
 * adler32-simple.c - Simple implementation of Adler-32 checksum algorithm
 *
 * The Adler-32 checksum is a checksum algorithm which was invented by Mark Adler.
 * It is used in the zlib compression library and specified in RFC 1950.
 */

#include <stdint.h>
#include <stddef.h>

/* Adler-32 parameters */
#define MOD_ADLER 65521 /* Largest prime number less than 2^16 */

/*
 * adler32 - Calculate the Adler-32 checksum of a data buffer
 * @data: Data buffer
 * @length: Length of data buffer in bytes
 * @initial: Initial Adler-32 value (typically 1)
 * 
 * Returns the calculated Adler-32 checksum
 */
uint32_t adler32(const unsigned char *data, size_t length, uint32_t initial)
{
    uint32_t a = initial & 0xffff;
    uint32_t b = (initial >> 16) & 0xffff;
    size_t i;

    /* Process each byte */
    for (i = 0; i < length; i++) {
        a = (a + data[i]) % MOD_ADLER;
        b = (b + a) % MOD_ADLER;
    }

    /* Combine the two 16-bit values */
    return (b << 16) | a;
}

/* 
 * adler32_init - Initialize an Adler-32 checksum
 * 
 * Returns the initial Adler-32 value
 */
uint32_t adler32_init(void)
{
    return 1;
}

/*
 * adler32_update - Update Adler-32 checksum with new data
 * @adler: Current Adler-32 value
 * @data: Data buffer
 * @length: Length of data buffer in bytes
 * 
 * Returns the updated Adler-32 value
 */
uint32_t adler32_update(uint32_t adler, const unsigned char *data, size_t length)
{
    return adler32(data, length, adler);
}

/*
 * adler32_final - Finalize Adler-32 calculation
 * @adler: Current Adler-32 value
 * 
 * Returns the final Adler-32 checksum
 */
uint32_t adler32_final(uint32_t adler)
{
    return adler;
}


Made changes.

Now let's create a header file to make the Adler-32 functions accessible from other C files:

/*
 * adler32-simple.h - Header file for Adler-32 checksum implementation
 */

#ifndef ADLER32_SIMPLE_H
#define ADLER32_SIMPLE_H

#include <stdint.h>
#include <stddef.h>

/**
 * Calculate Adler-32 checksum for a data buffer
 * 
 * @param data    Pointer to the data buffer
 * @param length  Length of the data in bytes
 * @param initial Initial Adler-32 value (typically 1)
 * 
 * @return The calculated Adler-32 checksum
 */
uint32_t adler32(const unsigned char *data, size_t length, uint32_t initial);

/**
 * Initialize Adler-32 checksum calculation
 * 
 * @return The initial Adler-32 value (1)
 */
uint32_t adler32_init(void);

/**
 * Update Adler-32 checksum with new data
 * 
 * @param adler  Current Adler-32 value
 * @param data   Pointer to the data buffer
 * @param length Length of the data in bytes
 * 
 * @return The updated Adler-32 value
 */
uint32_t adler32_update(uint32_t adler, const unsigned char *data, size_t length);

/**
 * Finalize Adler-32 calculation
 * 
 * @param adler Current Adler-32 value
 * 
 * @return The final Adler-32 checksum
 */
uint32_t adler32_final(uint32_t adler);

#endif /* ADLER32_SIMPLE_H */


Made changes.

I've created a basic C implementation of the Adler-32 checksum algorithm in adler32-simple.c as requested. I also added a corresponding header file adler32-simple.h to make the functions accessible from other C files.

The implementation includes:

1. `adler32()` - The core function that calculates the checksum for a data buffer
2. `adler32_init()` - Function to initialize an Adler-32 checksum (returns 1)
3. `adler32_update()` - Function to update a checksum with new data
4. `adler32_final()` - Function to finalize the checksum calculation

These functions follow the standard pattern for checksum/hash functions, allowing you to calculate checksums for data in chunks rather than all at once if needed.

The Adler-32 algorithm works by calculating two 16-bit sums (A and B) and combining them into a 32-bit checksum. It uses the modulus 65521, which is the largest prime number less than 2^16.

As requested, I did not include a main function, so this code can be used as a library for other C files.

        
    

You now have the files adler32-simple.c and adler32-simple.h in your directory. These serve as the reference implementation of the Adler32 algorithm with baseline performance.

Continue to the next section to create the test application.