Why is the wrong result shown for a certain value of the entered number?

Question

assembler

And again, the assembler, with an even number 8, gives the result 767, but I don’t understand why ... here is that part of the code (the entered value in al)

push    ax

        call    Calculation

Calculation:
        test  al, 1
        jnz   Odd    ;нечетное, переход на метку Odd
        jz    Even   ;четное, переход на метку Even

Odd:
        push    bp
        mov     bp,sp
        mov     al,[bp+4]
        mul     al
        pop     bp
        jmp     Show_AX
Even:
        push    bp
        mov     bp,sp
        mov     al,[bp+4]
        mov      bl, al
        mul     al
        mul     bl
        sub     al, 1
        pop     bp

Answer 1

No, that's right, you have 767 and should work, judging by your code.
8 * 8 * 8 = 512
512 + byte(0 - 1) = 512 + 255 = 767
let me translate your code into C for clarity

int Calculation(short value) {
    if (value % 2 == 1) {
        char value_l = (char)value; // use only lower 8 bit
        return value_l * value_l;
    } else {
        char value_l = (char)value; // use only lower 8 bit
        short first_mul = value_l * value_l;
        char mul_l = (char)first_mul; // use only lower 8 bit of result
        short second_mul = mul_l * value_l;
        second_mul = (second_mul & 0xFF00) + (char)second_mul - 1; // subtract 1 only from lower 8 bits
        return second_mul;
    }
}