A minimal hash function for C?

In C, a minimal hash function refers to a simple yet functionally complete hash function that maps input (typically strings or numbers) to a fixed-size integer value, commonly used as an index in arrays or data structures. A very basic yet versatile hash function employs a simple accumulation method, such as summing the ASCII values of each character in a string and then applying a modulo operation with a fixed number (e.g., the size of the hash table).

Here is a simple example of a string hash function:

c
#include <stdio.h>
#include <string.h>

#define TABLE_SIZE 100  // Assuming the hash table size is 100

unsigned int hash(const char *key) {
    unsigned int sum = 0;
    for (int i = 0; key[i] != '\0'; i++) {
        sum += key[i];  // Add the ASCII value of each character to sum
    }
    return sum % TABLE_SIZE;  // Modulo operation ensures the hash value falls within the valid range of the hash table
}

int main() {
    char *keys[] = {"example", "test", "hash", "function", NULL};
    for (int i = 0; keys[i] != NULL; i++) {
        printf("Hash for %s is %u\n", keys[i], hash(keys[i]));
    }
    return 0;
}

In this example, we define a hash function hash that takes a string key as input and returns an unsigned integer as the hash value. This function processes the string character by character, accumulating the ASCII values into an integer sum, and then applies a modulo operation on TABLE_SIZE to ensure the result stays within the valid range of the hash table.

Although this function is straightforward and can work in specific scenarios, it is not ideal as a hash function because it may result in a higher collision rate (where different inputs produce identical outputs). In practical applications, one may require a more sophisticated hash function, such as FNV-1a or MurmurHash, which offer better distribution and lower collision rates. However, for demonstrating how to implement and use a hash function, this example serves as an excellent starting point.