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aufgaben/sheet10/sol1/magic.s

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+; This is the assembly of:
+;
+;     fn is_prime(n: u64) -> bool {
+;         (2..n).all(|d| n % d != 0)
+;     }
+;
+; Of course, it was compiled in release mode. Thus, this is a primality test
+; which works for numbers >= 2.
+
+magic:
+    push    rbp         ; standard function prologue:
+    mov     rbp, rsp    ;     storing old rbp and setting new one
+
+    mov     rcx, rdi    ; copy function argument to rcx
+    mov     esi, 2      ; rsi = 2 (this will be our counter)
+
+.LBB0_1:
+    mov     al, 1       ; out = true (rax contains the return value)
+
+    cmp     rsi, rcx    ; if our counter is equal to our function argument
+    jae     .LBB0_4     ; (rsi == rcx) we will jump to the end (return)
+
+    xor     edx, edx    ; set rdx to 0 (just for the upcoming div instruction)
+    mov     rax, rcx    ; copy the function argument into rax temporarily
+                        ; (this is just for the next instruction)
+
+    div     rsi         ; divide rdx:rax by rsi (counter). The result is stored
+                        ; in rax and more importantly: the remainder is stored
+                        ; in rdx!
+
+    inc     rsi         ; increment our counter
+
+    test    rdx, rdx    ; if the remainder is NOT 0, we will jump up
+    jne     .LBB0_1     ; again (keep going). Else we will just continue...
+
+    xor     eax, eax    ; out = false
+.LBB0_4:
+    pop     rbp         ; standard function epilogue
+    ret