CrazyBus RNG (C translation)

#include <stdio.h>
#include <inttypes.h>

inline uint64_t swap64( uint64_t n, _Bool high ) {
    if( high ) {
        return  ( ( n >> 16 ) & 0x0000FFFF00000000 ) |
                ( ( n << 16 ) & 0xFFFF000000000000 ) |
                ( n & 0x00000000FFFFFFFF );
    } else {
        return  ( ( n >> 16 ) & 0x000000000000FFFF ) |
                ( ( n << 16 ) & 0x00000000FFFF0000 ) |
                ( n & 0xFFFFFFFF00000000 );
    }
}

// RNG state
uint64_t rnd;

uint32_t long_rnd( void ) {
    register uint64_t a,     b;
    //                D0+D1, D2+D3
    a = ( rnd & 0xFFFFFFFFFFFFFF0E ) | 0x20;
    b = a;
    b *= 2;
    a += b;

    b = swap64( b, 1 );
    b = swap64( b, 0 );

    b = ( b & 0xFFFF0000FFFF0000 ) | ( ( b & 0xFFFF ) << 32 );
    a += b;
    rnd = a;
    return (uint32_t)( a >> 32 );
}

uint32_t random_seed( uint64_t seed ) {
    seed += ( seed << 32 );
    rnd = seed;
    return long_rnd();
}

uint32_t random_seed_crazybus( uint32_t seed ) {
    uint32_t garbage; // uninitialized
    garbage += seed;
    rnd = garbage; rnd <<= 32; rnd |= seed;
    return long_rnd();
}

uint16_t gen_random( uint16_t range ) {
    if( range > 0 )
        range = ( long_rnd() >> 16 ) % range;
    return range;
}

// testing
int main( void ) {
    int i;

    printf( "%016"PRIX64"\n", rnd );
    random_seed( 1 );
    printf( "%016"PRIX64"\n", rnd );

    for( i = 0; i < 16; ++i )
        printf( "%u\n", gen_random( 65535 ) );

    return 0;
}