gopher bitswap

#include <cstdio>
#include <cstring>

unsigned char rom[0x1000000];

//            0123456789ABCDEF6789012
char str[] = "abcdefghtijklmnoprsuqvw";

int convert(int a)
{
    int r = 0;
    for (int i=0; i<23; ++i)
    {
        if (a&(1<<(strchr(str,'a'+i)-str)))
            r|=(1<<i);
    }
    return r;
}

int convert2(int a)
{
    int r = 0;
    for (int i=0; i<23; ++i)
    {
        if (a&(1<<i))
            r|=(1<<(strchr(str,'a'+i)-str));
    }
    return r;
}

int main(int argc, char **args)
{
    if (argc != 4)
    {
        printf("gopher_bitswap.exe from|to input output");
        return 0;
    }
    FILE *f = fopen(args[2],"rb");
    if (!f)
        return 0;

    fread(rom,1,sizeof(rom),f);
    fclose(f);

    f = fopen(args[3],"wb");
    if (!f)
        return 0;

    bool from = true;
    if (!strcmp(args[1],"to"))
        from = false;
    for (int i=0; i<sizeof(rom); ++i)
    {
        int idx = (from?convert(i>>1):convert2(i>>1));
        unsigned char q = rom[(idx<<1)|(i&1)];
        fwrite(&q,1,1,f);
    }
    fclose(f);

    return 0;
}