Create a Lookup Table for ascii Conversions

create_cnv_ascii.c

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

//
// Create entries for a boolean lookup table to be used for character conversions.
//
// Example output from list[], below:
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 , '-', '.',  0 ,
//  	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 , 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
//  	'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 , 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
//  	'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',  0 ,  0 ,  0 ,  0 ,  0 ,
//
// Copy that to an array.
// static const uint8_t cnv_char_host[128] = {
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,  0 , '-', '.',  0 ,
//  	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',  0 ,  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 , 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
//  	'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',  0 ,  0 ,  0 ,  0 ,  0 ,
//  	 0 , 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
//  	'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',  0 ,  0 ,  0 ,  0 ,  0 ,
// };
//
// Call by:
// if ( cnv_char_host[str[i]] ) { ... }
//
// Why?
// A lookup table that converts your data is even faster than isalpha()
// isalpha          : 0.582884
// cnv_char_host    : 0.300070
// With that table, I'll have already tested and converted two characters just as
// isalpha() is finishing figuring out if it's a letter.
//
// Especially for more complex checks, e.g. valid url characters, speed improves
// significantly over other methods.
//
// And at 128 bytes per table, it works out well.
//

int main(){

	char listfrm[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-.";
	char listto[]  = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789-.";
	int  len  = strlen(listfrm);
	int  max  = 128;
	int  fnd  = 0;
	int  splt = 16;		// How many chars before a line break

	int i, j;
	for ( i=0; i<max; ++i ) {
		fnd = 0;
		for ( j=0; j<len; ++j ) {
			if ( listfrm[j] == i ) {
				printf("'%c', ", listto[j]);
				fnd = 1;
				break;
			}
		}
		if (!fnd)
			printf(" 0 , ");
		if ( (i % splt) == (splt-1) )
			printf("\n");
	}
	printf("\n");

	return 1;
}

If you just want to create a lookup table for boolean checks:
https://gist.github.com/benwills/d514f2d9b5846c147e71