[Solved] Is there any way I can make my function for testing the equality of strings even faster?

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Your first function just do not work and is wrong.

You do not the correct parameter types. Do not use register as it has no effect at all. Register is ignored at any level of optimization. Compilers are better than me or you in micro optimizations – so help the compiler optimizer with the const and restrict when applicable.

The second one can be simplified.

int stringsequal1(const char *restrict s1, const char *restrict s2)
{
    do
    {
        if(*s1 != *s2) return 0;
    }
    while(*s1++ + *s2++);
    return 1;
}

and thew result code for both is:

int stringsequal1(const char *s1, const char *s2)
{
    do
    {
        if(*s1 != *s2) return 0;
    }
    while(*s1++ + *s2++);
    return 1;
}

stringsequal1:
        xor     edx, edx
        jmp     .L11
.L15:
        add     rdx, 1
        add     eax, eax
        je      .L14
.L11:
        movsx   eax, BYTE PTR [rdi+rdx]
        cmp     al, BYTE PTR [rsi+rdx]
        je      .L15
        mov     eax, 1
        ret
.L14:
        ret

int stringsequal2(register char *s1, register char *s2)
{
    while(1)
    {
        if(!((*s1 + *s2) ^ 0)) return 1;
        if(*(s1 ++) ^ *(s2 ++)) break;
    }
    return 0;
}

stringsequal2:
        xor     eax, eax
        jmp     .L18
.L22:
        add     rax, 1
        cmp     cl, r9b
        jne     .L21
.L18:
        movsx   r8d, BYTE PTR [rdi+rax]
        movsx   r9d, BYTE PTR [rsi+rax]
        mov     ecx, r8d
        add     r8d, r9d
        jne     .L22
        mov     eax, 1
        ret
.L21:
        xor     eax, eax
        ret

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solved Is there any way I can make my function for testing the equality of strings even faster?