;; file: big_math.asm; Defines asm routines that add and subtract Big_ints; There is a lot of common code between the add and subtract routines.;segment .datasegment .bss segment .text        global  _add_big_ints, _sub_big_ints;; A Big_int class is represented by a struct with a unsigned DWORD named ; size_ and a DWORD pointer named number_. An instance looks like:;  +---------+;  | size_   |  offset = 0;  +---------+;  | number_ |  offset = 4;  +---------+;%define size_offset 0%define number_offset 4%define EXIT_OK 0%define EXIT_OVERFLOW 1%define EXIT_SIZE_MISMATCH 2;; Parameters for both add and sub routines;;Pointer to the Big_int to store result into%define res ebp+8;; Pointer to the first Big_int to add or sub%define op1 ebp+12;; Pointer to the second Big_int to add or sub%define op2 ebp+16;; int add_big_ints(Big_int & res, const Big_int & op1, const Big_int & op2);; res at [ebp + 8]; op1 at [ebp + 12]; op2 at [ebp + 16];_add_big_ints:        push    ebp        mov     ebp, esp        push    ebx        push    esi        push    edi        ;        ; first set up esi to point to op1        ;              edi to point to op2        ;              ebx to point to res        ;               mov     esi, [op1]        mov     edi, [op2]        mov     ebx, [res]        ;        ; make sure that all 3 Big_int's have the same size        ;        mov     eax, [esi + size_offset]        cmp     eax, [edi + size_offset]        jne     sizes_not_equal                 ; op1.size_ != op2.size_        cmp     eax, [ebx + size_offset]        jne     sizes_not_equal                 ; op1.size_ != res.size_        mov     ecx, eax                        ; ecx = size of Big_int's        ;        ; now, set registers to point to their respective arrays        ;      esi = op1.number_        ;      edi = op2.number_        ;      ebx = res.number_        ;        mov     ebx, [ebx + number_offset]        mov     esi, [esi + number_offset]        mov     edi, [edi + number_offset]                clc                                     ; clear carry flag        xor     edx, edx                        ; edx = 0        ;        ; addition loop        ;add_loop:        mov     eax, [edi+4*edx]        adc     eax, [esi+4*edx]        mov     [ebx + 4*edx], eax        inc     edx                             ; does not alter carry flag        loop    add_loop        jc      overflowok_done:        xor     eax, eax                        ; return value = EXIT_OK        jmp     doneoverflow:        mov     eax, EXIT_OVERFLOW        jmp     donesizes_not_equal:        mov     eax, EXIT_SIZE_MISMATCHdone:        pop     edi        pop     esi        pop     ebx        leave        ret;; int sub_big_ints(Big_int & res, const Big_int & op1, const Big_int & op2);; Computes res = op1 - op2; This routine uses some of the add_big_ints routine code!; res at [ebp + 8]; op1 at [ebp + 12]; op2 at [ebp + 16];_sub_big_ints:        push    ebp        mov     ebp, esp        push    ebx        push    esi        push    edi                ;        ; first set up esi to point to op1        ;              edi to point to op2        ;              ebx to point to res        ;               mov     esi, [op1]        mov     edi, [op2]        mov     ebx, [res]        ;        ; make sure that all 3 Big_int's have the same size        ;        mov     eax, [esi + size_offset]        cmp     eax, [edi + size_offset]        jne     sizes_not_equal        cmp     eax, [ebx + size_offset]        jne     sizes_not_equal        mov     ecx, eax        ;        ; now, point registers to point to their respective arrays        ;      esi = op1.number_        ;      edi = op2.number_        ;      ebx = res.number_        ;        mov     ebx, [ebx + number_offset]        mov     esi, [esi + number_offset]        mov     edi, [edi + number_offset]        clc        xor     edx, edx        ;        ; subtraction loop        ;sub_loop:        mov     eax, [esi+4*edx]        sbb     eax, [edi+4*edx]        mov     [ebx + 4*edx], eax        inc     edx        loop    sub_loop        jnc     ok_done        jmp     overflow