037.asm

section .data
    msg db "%d", 10, 0          ;return string for printf (just the result)
    primes times 125000 db 255  ;array for the prime sieve

section .text
    extern printf
    global main

main:
    xor     ebx, ebx        ;array index for outer loop
    btr     [primes], ebx   ;set 0 and 1 to not prime
    inc     ebx
    btr     [primes], ebx

sieve_outer:
    inc     ebx             ;increase index
    mov     eax, ebx        ;copy to eax for squaring
    mul     ebx             ;square
    cmp     eax, 1000000    ;check if square is > limit    
    jg      reset           ;if it is, jump to reset
    bt      [primes], ebx   ;check if ebx is not prime
    jnc     sieve_outer     ;if not prime, try next number

sieve_inner:
    btr     [primes], eax   ;set multiple to not prime
    add     eax, ebx        ;next multiple
    cmp     eax, 1000000    ;check if square is <= limit
    jl      sieve_inner     ;if it is, continue with inner loop
    jmp     sieve_outer     ;if not, continue with outer loop

reset:
    mov     ebx, 10         ;10 in ebx (primes < 10 not considered)
    mov     edi, 10         ;10 in edi for divisions
    xor     ecx, ecx        ;sum
    xor     r8d, r8d        ;counter

nextprime:
    inc     ebx             ;next number
    bt      [primes], ebx   ;is it prime?
    jnc     nextprime       ;if not, find next prime
    mov     eax, ebx        ;prime in eax for next step

trunc_right:
    xor     edx, edx        ;reset remainder
    div     edi             ;divide by 10
    bt      [primes], eax   ;is truncated number prime?
    jnc     nextprime       ;if not, try next prime
    cmp     eax, 10         ;number still >= 10?
    jge     trunc_right     ;if yes, repeat
    mov     esi, 1000000    ;1000000 in esi for division
    mov     eax, esi        ;copy to eax for next step

setdivisor:
    xor     edx, edx        ;reset remainder
    div     edi             ;divide by 10
    cmp     eax, ebx        ;eax < number?
    jg      setdivisor      ;if not, repeat
    mov     esi, eax        ;else set esi
    mov     eax, ebx        ;prime in eax

trunc_left:
    xor     edx, edx        ;reset remainder
    div     esi             ;divide by esi
    mov     eax, edx        ;remainder in eax
    bt      [primes], eax   ;is remainder prime?
    jnc     nextprime       ;if not try next prime
    push    rax             ;result on the stack
    mov     eax, esi        ;esi in eax
    xor     edx, edx        ;reset remainder
    div     edi             ;divide by 10
    mov     esi, eax        ;result back in esi
    pop     rax             ;number back from the stack
    cmp     eax, 10         ;number still >= 10?
    jge     trunc_left      ;if yes, repeat
    add     ecx, ebx        ;else add prime to sum
    inc     r8d             ;increase counter
    cmp     r8d, 11         ;are all 11 candidates found?
    jl      nextprime       ;if not, try next prime

print:                  ;printing routine, differs slightly from OS to OS
    push    rbp
    mov     edi, msg
    mov     esi, ecx
    call    printf
    pop     rbp

exit:                   ;exit routine, dito
    mov     eax, 1
    xor     edi, edi
    syscall

section .note.GNU-stack ;just for gcc