X86 INSTRUCTIONS:::AIRTHMETIC INSTRUCTION

Arithmetic instructions take two operands: a destination and a source. The destination must be a register or a memory location. The source may be either a memory location, a register, or a constant value. Atleast one of the two must be a register, because operations may not use a memory location as both a source and a destination. Syntax 1 : add src, dest #GAS Syntax add dest, src #Intel syntax This adds src to dest. If you are using the MASM syntax, then the result is stored in the first argument, if you are using the GAS syntax, it is stored in the second argument. Syntax 2 : sub src, dest #GAS Syntax sub dest, src #Intel syntax Like ADD, only it subtracts source from destination instead. In C: dest -= src; Syntax 3 : mul arg This multiplies "arg" by the value of corresponding byte-length in the AX register. operand size 1 byte 2 bytes 4 bytes other operand AL AX EAX higher part of result stored in: AH DX EDX lower part of result stored in: AL AX EAX In the second case, the target is not EAX for backward compatibility with code written for older processors. Syntax 4 : imul arg As MUL, only signed. The IMUL instruction has the same format as MUL, but also accepts two other formats like so: Syntax 5 : imul src, dest #GAS Syntax imul dest, src #Intel syntax This multiplies src by dest. If you are using the NASM syntax, then the result is stored in the first argument, if you are using the GAS syntax, it is stored in the second argument. Syntax 6 : imul aux, src, dest #GAS Syntax imul dest, src, aux #Intel syntax This multiplies src by aux and places it into dest. If you are using the NASM syntax, then the result is stored in the first argument, if you are using the GAS syntax, it is stored in the third argument. Syntax 7 : div arg This divides the value in the dividend register(s) by "arg", see table below. divisor size 1 byte 2 bytes 4 bytes dividend AX DX:AX EDX:EAX remainder stored in: AH DX EDX quotient stored in: AL AX EAX The colon (:) means concatenation. With divisor size 4, this means that EDX are the bits 32-63 and EAX are bits 0-31 of the input number (with lower bit numbers being less significant, in this example). As you typically have 32-bit input values for division, you often need to use CDQ to sign-extend EAX into EDX just before the division. If quotient does not fit into quotient register, arithmetic overflow interrupt occurs. All flags are in undefined state after the operation. Syntax 8 : idiv arg As DIV, only signed. Syntax 9 : neg arg Arithmetically negates the argument (i.e. two's complement negation).