Quickly Create a Binary Lookup Table

create_lkp_bool.c

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

//
//  Create entries for a boolean lookup table.
//
// 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,
// 	0,1,0,1,1,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,
// 	1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,
// 	0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,1,0,
//
// Copy that to an array.
//  static const uint8_t lu_bool_url[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,
//  	0,1,0,1,1,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,
//  	1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,
//  	0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,1,0,
//  };
//
// Call by:
// if ( lu_bool_url[str[i]] ) { ... }
//
// Why?
// A lookup table is even faster than isalpha()
// isalpha       : 0.489370
// lu_bool_alpha : 0.331028
//
// 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 list[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~:/?#[]@!$&'()*+,;=";
	int  len  = strlen(list);
	int  max  = 128;
	int  fnd  = 0;
	int  splt = 32;		// 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 ( list[j] == i ) {
				printf("1,");
				fnd = 1;
				break;
			}
		}
		if (!fnd)
			printf("0,");
		if ( (i % splt) == (splt-1) )
			printf("\n");
	}
	printf("\n");

	return 1;
}

If you want to create a lookup table for converting characters:
https://gist.github.com/benwills/22b707b30e620764220b