Addition & Subtraction

Adding and subtracting works almost the same as moving.

add <dest>, <src>
Reads from <dest> and <src> and writes the sum of the two to <dest>

sub <dest>, <src>
Reads from <dest> and <src> and writes <dest> - <sub> to <dest>

Example:

add dword[y], 5 ; i.e.t. y+=5
add rax, 12     ; i.e.t. rax+=12
add rax, rdx    ; i.e.t. rax+=rdx

In order to do more advanced operations, such as y=x+z, you need to split it up into the most basic steps:

mov r10d, dword[z]
add dword[x], r10d ; i.e.t. x += z
mov r11d, dword[x]
mov dword[y], r11d ; i.e.t. y + x + z

Notice how registers are being used to store the inbetween steps.

That is all there is to know for addition and subtraction.

Examples

The following examples are unchecked and may be wrong.

x = y + 5

add dword[y], 5 i.e.t. y += 5
mov r11d, dword[y]
mov dword[x], r11d i.e.t. x = y + 5

y++;

inc dword[y] or inc rax

x—;

dec dword[y] or dec rax

y = x + (z + 32)

add dword[z], 32 i.e.t. z + 32
mov r14d, dword[z]
add dword[x], r14d i.e.t. x + (z + 32)
mov r15d, dword[x]
mov dword[y], r15d i.e.t. y = x + (z + 32)

y = x - (z + 32)

add dword[z], 32 i.e.t. z + 32
mov r14d, dword[z]
sub dword[x], r14d
mov r15d, dword[x]
mov dword[y], r15d

z = x++ + (y - 32)

sub dword[y], 32 i.e.t. y - 32
mov r13d, dword[x]
add r13d, dword[y] i.e.t. y + (y - 32)
mov dword[z], r13d i.e.t. x++

z = ++x + (y - 32)

sub dword[y], 32 i.e.t. y - 32
mov dword[z], r13d i.e.t. ++x
mov r13d, dword[x]
add r13d, dword[y] i.e.t. y + (y - 32)

a = b + c

mov r8d, dword[c]
add r8d, dword[b] i.e.t. b + c
mov dword[a], r8d i.e.t. a = b + c

a = c + b

mov r8d, dword[b]
add r8d, dword[c] i.e.t. c + b
mov dword[a], r8d i.e.t. a = c + b

a = b - c

mov r8d, dword[b]
sub r8d, dword[c] i.e.t. b - c
mov dword[a], r8d i.e.t. a = b - c