Proposal for Optimized Character Type Function

[The Cuthour]

Hi,

I am writing to propose an enhancement to the character type functions 
such as isalpha(), isupper(), and islower() through the use of optimized 
lookup tables. By using a single lookup table with bitwise operations, 
we can achieve efficient and concise implementations for these 
functions. Below is a brief overview of the proposed implementation:

unsigned char type_table[256] = {
     // ... initialization
};

const bool my_islower(const unsigned char ch) {
     return type_table[ch] & 0x01;
}

const bool my_isupper(const unsigned char ch) {
     return type_table[ch] & 0x02;
}

const bool my_isalpha(const unsigned char ch) {
     return type_table[ch] & 0x03;
}

This approach leverages a lookup table with predefined values, enabling 
fast and straightforward character type determination using bitwise 
operations. This method is not only efficient but also simplifies the 
code and enhances readability.