Shift case

caseshift.cpp

#include <cstdio>
#include <cstring>
#include <random>
#include <cctype>

int main(int argc, char *argv[]) {
    std::FILE *ifp = argc > 1 ? std::fopen(argv[1], "rb"): stdin,
              *ofp = argc > 2 ? std::fopen(argv[2], "wb"): stdout;
    int c;
    static constexpr int arr[]{0,32};
    std::mt19937_64 mt(argc + (argc == 1 ? 1337: std::strlen(argv[1])));
    long long unsigned v = mt();
    unsigned char count = 64;
    while((c = getc_unlocked(ifp)) >= 0) {
        if(std::isalpha(c)) {
            c ^= arr[v&1], v>>=1;
            if(__builtin_expect(--count == 0, 0))
                count = 64, v = mt();
        }
        std::fputc(c, ofp);
    }
    if(ifp != stdin) std::fclose(ifp);
    if(ofp != stdout) std::fclose(ofp);
}

#if 0
Daniels-MacBook-Pro:caseshift dnb$ cat caseshift.cpp | ./caseshift 
#iNCLude <CSTDio>
#InCLudE <cStrING>
#include <RanDoM>
#IncLUDE <CcTyPE>

inT mAin(INT ARGC, ChAr *ARgV[]) {
    STD::FIlE *ifp = argc > 1 ? sTd::FoPen(aRgv[1], "Rb"): STdin,
              *ofp = Argc > 2 ? STd::FopeN(aRGv[2], "wb"): STdOuT;
    INt c;
    STATIC cOnStEXPr INt arr[]{0,32};
    sTD::MT19937_64 mt(ARGC + (aRgC == 1 ? 1337: STD::StRLen(ARGV[1])));
    LONG long unSiGNED V = mt();
    uNSIgneD cHAr CoUNT = 64;
    wHIlE((c = GETc_unLoCKed(ifP)) >= 0) {
        If(std::iSAlpHA(c)) {
            c ^= ARr[V&1], v>>=1;
            If(__builtin_expECT(--COuNT == 0, 0))
                cOunT = 64, v = Mt();
        }
        StD::fPuTC(c, OFp);
    }
    iF(IFp != sTDin) STD::FCLoSE(IfP);
    If(Ofp != StdouT) sTD::FcloSe(OfP);
}
#endif