#include <stdio.h>
#include <stdint.h>

uint64_t *bits = (uint64_t[64]) { 0 };
uint64_t top = 0;

/* gcc push-bit.c -O3 && objdump -D a.out | less
0000000000001240 <get_bit>:
    1240:       48 8b 05 f1 2d 00 00    mov    0x2df1(%rip),%rax        # 4038 <bits>
    1247:       48 89 fa                mov    %rdi,%rdx
    124a:       48 c1 ea 06             shr    $0x6,%rdx
    124e:       48 8b 04 d0             mov    (%rax,%rdx,8),%rax
    1252:       48 0f a3 f8             bt     %rdi,%rax
    1256:       0f 92 c0                setb   %al
    1259:       0f b6 c0                movzbl %al,%eax
    125c:       c3                      ret
    125d:       0f 1f 00                nopl   (%rax)
*/

uint64_t
get_bit (uint64_t const addr) {
        uint64_t const shift = addr & (uint64_t) 0b111111;
        uint64_t const index = addr >> 6;

        return (bits[index] >> shift) & 1;
}

/* gcc push-bit.c -O3 && objdump -D a.out | less
0000000000001260 <set_bit>:
    1260:       48 8b 05 d1 2d 00 00    mov    0x2dd1(%rip),%rax        # 4038 <bits>
    1267:       48 89 fa                mov    %rdi,%rdx
    126a:       48 89 f9                mov    %rdi,%rcx
    126d:       83 e6 01                and    $0x1,%esi
    1270:       48 c1 ea 06             shr    $0x6,%rdx
    1274:       48 d3 e6                shl    %cl,%rsi
    1277:       48 8d 14 d0             lea    (%rax,%rdx,8),%rdx
    127b:       48 c7 c0 fe ff ff ff    mov    $0xfffffffffffffffe,%rax
    1282:       48 d3 c0                rol    %cl,%rax
    1285:       48 23 02                and    (%rdx),%rax
    1288:       48 09 f0                or     %rsi,%rax
    128b:       48 89 02                mov    %rax,(%rdx)
    128e:       c3                      ret
    128f:       90                      nop
*/

void
set_bit (uint64_t const addr, uint64_t const value) {
        uint64_t const shift = addr & (uint64_t) 0b111111;
        uint64_t const index = addr >> 6;

        bits[index] &= ~((uint64_t) 1 << shift); // clear
        bits[index] |= ((value & 1) << shift);   // set
}

void
push_bit (uint64_t const value) {
        set_bit(top, value);
        top++;
}

void
print_bits (void) {
        printf(":: ");
        for (uint64_t i = 0; i < top; i++) {
                putchar(get_bit(i) ? '1' : '0');
                if (i > 0 && (i + 1) % 4 == 0) {
                        putchar('.');
                }
        }
        putchar('\n');
}

int
main (int argc, char const **argv) {
        printf("[%s, Press Ctrl+D or Ctrl+C to Quit]\n", argv[0]);
        printf("[Type 0 or 1 to push a bit, Type P to print stack]\n");
        while (!feof(stdin)) {
                int const c = getchar();
                switch (c) {
                break; case '0': push_bit(0);
                break; case '1': push_bit(1);
                break; case 'p': print_bits();
                }
        }
        return 0;
}