Bitboolbench Solution 2

solution2.c

// Here is also a version with always_inline; https://godbolt.org/z/1hcvv65Pv
// performance is basically the same.
#include <stdio.h>
#define uint unsigned int

struct Bits
{
    unsigned b0:1, b1:1, b2:1, b3:1, b4:1, b5:1, b6:1, b7:1;
};
union CBits
{
    struct Bits bits;
    unsigned char byte;
};

int main()
{
        uint i = 0;
        unsigned char by;

        union CBits a;
        // set bools
        a.bits.b0 = i;
        a.bits.b1 = i-1;
        a.bits.b2 = i-2;
        a.bits.b3 = i-3;
        a.bits.b4 = i-4;
        a.bits.b5 = i-5;
        a.bits.b6 = i-6;
        a.bits.b7 = i-7;
        // bools to byte
        by = a.byte;
        // byte to bools
        uint bo[8] ={
                        a.bits.b0,
                        a.bits.b1,
                        a.bits.b2,
                        a.bits.b3,
                        a.bits.b4,
                        a.bits.b5,
                        a.bits.b6,
                        a.bits.b7,
                    };   

        printf("%c\n", by + bo[0] + bo[1] + bo[2] + bo[3] + bo[4] + bo[5] + bo[6] + bo[7]);
        return 0;
}

/*
main:
        push    rbp
        mov     rbp, rsp
        sub     rsp, 48
        mov     DWORD PTR [rbp-4], 0

// set bools
        mov     eax, DWORD PTR [rbp-4]
        and     eax, 1
        and     eax, 1
        mov     edx, eax
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -2
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 1
        and     eax, 1
        and     eax, 1
        lea     edx, [rax+rax]
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -3
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 2
        and     eax, 1
        and     eax, 1
        lea     edx, [0+rax*4]
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -5
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 3
        and     eax, 1
        and     eax, 1
        lea     edx, [0+rax*8]
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -9
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 4
        and     eax, 1
        and     eax, 1
        sal     eax, 4
        mov     edx, eax
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -17
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 5
        and     eax, 1
        and     eax, 1
        sal     eax, 5
        mov     edx, eax
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -33
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 6
        and     eax, 1
        and     eax, 1
        sal     eax, 6
        mov     edx, eax
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, -65
        or      eax, edx
        mov     BYTE PTR [rbp-12], al
        mov     eax, DWORD PTR [rbp-4]
        sub     eax, 7
        and     eax, 1
        sal     eax, 7
        mov     edx, eax
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, 127
        or      eax, edx
        mov     BYTE PTR [rbp-12], al

// bools to byte
        movzx   eax, BYTE PTR [rbp-12]
        mov     BYTE PTR [rbp-5], al

// byte to bools
        movzx   eax, BYTE PTR [rbp-12]
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-48], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-44], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 2
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-40], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 3
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-36], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 4
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-32], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 5
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-28], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 6
        and     eax, 1
        movzx   eax, al
        mov     DWORD PTR [rbp-24], eax
        movzx   eax, BYTE PTR [rbp-12]
        shr     al, 7
        movzx   eax, al
*/