Update

Author: INIT-REF

086.asm

@@ -1,47 +1,108 @@
-section .data
-    msg db "%d", 10, 0  ;return string for printf (just the result)
-
-section .text
-    extern printf
-    global main
-
-main:
-    xor     ebx, ebx    ;r in Dickson's method
-    xor     r10d, r10d  ;cuboids
-
-next:
-    add     ebx, 2      ;the next even r (odd values not allowed)
-    mov     eax, ebx    ;put number in eax for multiplication
-    mul     ebx         ;square
-    shr     eax, 1      ;half
-    mov     ecx, eax    ;put r^2 / 2 in ecx
-    xor     edi, edi    ;for divisors of r^2 / 2
-
-triplets:
-    inc     edi         ;next divisor candidate
-    mov     eax, edi    ;candidate in eax
-    mul     edi         ;square
-    cmp     eax, ecx    ;check if square of candidate is less than r^2 / 2
-    jg      next        ;if not, go to next higher r
-    xor     edx, edx    ;prepare remainder
-    mov     eax, ecx    ;r^2 / 2 in eax for division
-    div     edi         ;divide by current divisor
-    test    edx, edx    ;check if remainder is zero
-    jnz     triplets    ;if not, continue with next divisor
-    inc     r10d
-    cmp     r10d, 1975
-    jl      triplets    
-
-print:                  ;printing routine, differs slightly from OS to OS
-    push    rbp
-    mov     edi, msg
+format ELF64 executable 9
+
+segment readable writable
+    result: times 10 db 0       ;empty string for printing the result later
+                     db 10, 0
+
+segment readable executable
+    entry start
+
+start:
+    mov     eax, 1          ;length
+    xor     ecx, ecx        ;counter
+
+next_l:
+    cmp     ecx, 1000000    ;count > 1e6?
+    jg      finished        ;if yes, we are finished
+    inc     eax             ;next length
+    mov     edx, eax        ;in edx
+    shl     edx, 1          ;2 * l as limit of next loop
+    mov     ebx, 3          ;init width + height
+
+next_wh:
+    mov     edi, eax
+    imul    edi, eax        ;l^2
     mov     esi, ebx
-    call    printf
-    pop     rbp
+    imul    esi, ebx        ;(w + h)^2
+    add     edi, esi        ;l^2 + (w + h)^2
+    test    edi, 1          ;is result even (last bit 0)?
+    jz      even            ;if yes, jump directly to even
+
+mod_8:
+    mov     esi, edi        ;any odd perfect square must be 1 (mod 8)
+    and     esi, 7
+    cmp     esi, 1
+    jne     skip_count
+    jmp     even
+
+even:
+    mov     esi, edi        ;while n is a power of 4, shift right 2 bits
+    and     esi, 3
+    test    esi, esi
+    jnz     and_7
+    shr     edi, 2
+    jmp     even
+
+and_7:                      ;if result & 7 != 1, n is not a perfect square
+    mov     esi, edi
+    and     esi, 7
+    cmp     esi, 1
+    jne     skip_count
+
+    mov     esi, 1          ;prepare for squaretest
+    mov     r8d, 1
 
-exit:                   ;exit routine, dito
+squaretest:
+    add     r8d, 2
+    add     esi, r8d
+    cmp     esi, edi
+    jl      squaretest
+    jg      skip_count
+
+is_square:
+    cmp     ebx, eax        ;is w + h <= l?
+    jle     not_greater     ;if yes, jump to not_greater
+    mov     edi, ebx        ;else calclulate (l - ((w + h + 1) / 2)) + 1
+    mov     esi, eax
+    inc     edi
+    shr     edi, 1
+    sub     esi, edi
+    inc     esi
+    add     ecx, esi        ;add result to count and continue
+    jmp     skip_count
+
+not_greater:
+    mov     edi, ebx        ;calculate (w + h) / 2
+    shr     edi, 1
+    add     ecx, edi        ;and add to count
+
+skip_count:
+    inc     ebx             ;next width + height
+    cmp     ebx, edx        ;<= 2 * l?
+    jle     next_wh         ;if yes, repeat
+    jmp     next_l          ;else take next l
+
+finished:
+    mov     ebx, 10
+    mov     ecx, 9
+
+convert_result:
+    xor     edx, edx
+    div     ebx
+    add     edx, '0'
+    mov     [result + ecx], dl
+    dec     ecx
+    test    eax, eax
+    jnz     convert_result
+
+print:
+    mov     eax, 4
+    mov     edi, 1
+    mov     esi, result
+    mov     edx, 12
+    syscall
+
+exit:
     mov     eax, 1
     xor     edi, edi
     syscall
-
-section .note.GNU-stack ;just for gcc