Another demo for the C++ hexdump of previous gist (need the hxd.hpp)

fl.cpp

/* Compile with $ g++ -o fl fl.cpp
 * Project Crew™ 12/28/2025
 */

#include <iostream>
#include <iomanip>
using namespace std;

#include "fl.hpp"
#include "hxd.hpp"

//#define DBG     1
#define MYB     "Lorem ipsum dolor sit amet, " \
                "consectetuer adipiscing elit."

void
fl (unsigned char *myb, unsigned long int mybsize)
{
/* turn the string to unprintable junk chars */
    unsigned long int c;
    /* register */ uint8_t t;
    
    for(c = 0; c < mybsize - 1; c++)
    {
#ifdef DBG
        cout << c << ' ';
#endif
        t = myb[c];                     // take each char and ...
        t += A;                         // add (pretty obvious)
        t = lrot8(t, S);                // bitwise nybble swap
        t ^= W;                         // ...     NOT
        t -= A;                         // subtract
        myb[c] = t;                     // store back to array
    }
}

int
main()
{
    unsigned char myb[] = MYB;
    unsigned long int mybsize = sizeof(myb);

    fl(myb, mybsize);

/* take a lQQk at what we got */
    hxd(myb, mybsize);
    
    cout << "\n\n";
    cout << '"' << myb << '"' << endl;
}

fl.hpp

#ifndef CHAR_BIT
#define CHAR_BIT 8
#endif

#define A 3                             // temp + A... - A
#define S 4                             // byte swap
#define W -1                            // temp xor 0xff (-1) = NOT temp

/* 8-bit bitwise rotate, should compile to a ror/rol (x86)
 * How we rotate before the std::bit in C++20 */
static inline uint8_t
lrot8 (uint8_t c, unsigned int n)
{
    const unsigned int mask = (CHAR_BIT*sizeof(c) - 1);
    
    // assert ( (c<=mask) &&"rotate by type width or more");
    n &= mask;                                  // o <= N
    return (c << n) | (c >> ( (-n) & mask) );   // do rotate
    /* flip the << shift >> to rotate the other way */
}