Arithmetic and logical operations

Write it at the front

Pictured here x86-64 Some integer and logical operations of . Most of these instructions have various variants with operands of different sizes .eg：ADD It consists of four addition instructions : addb、addw、addl and addq, They are byte addition 、 Word addition 、 Double word addition and four word addition ;lea Command variant ( Sort by size ):leaw 、leal、leaq, They are word addition 、 Double word addition and four word addition .

  These operations are divided into four groups ： Load valid address 、 Unitary operation 、 Binary operation and shift . One of the unary operations has an operand , Binary operations have two operands .

Load valid address leaq

leaq  S,D

leaq： In form, it reads data from memory to register , In fact, the valid address is written to the destination operand .

eg：

c Language

        long scale(long x,long y,long z){

                long t = x +4* y + 12*Z;

                return t;}

Compile time , The arithmetic operation of this function takes three leaq Instructions implement ：

        long scale(long x, long y,long z)

        x in %rdi, y in %rsi,z in %rdx

        scale：

                leaq         (%rdi,%rsi,4),%rax      //x+4*y

                leaq        (%rdx, %rdx,2),%rdx    //z +2*z =3*z

                leaq        (%rax,%rdx,4), %rax        //(x+4*y)+4*(3*z)=x +4*y +12*z

                ret

Unary and binary operations

Unitary operation

  A unary operation has only one operand , This operand even if the source operand is the destination operand , The operand can be a register , It can also be a memory location .

eg：decq (%rsp)           // Make stack top 8 Byte element -1    Be similar to C In language --

        incq (%rsp)            // Make stack top 8 Byte element +1   Be similar to C In language ++

Binary operation

Binary operations have two operands , The second operand is both the source operand and the destination operand . This grammar is similar to C Assignment operators in languages , for example x-=y.

The first operand source operand can be an immediate number 、 Register or memory location .

The operand of the second operand can be a register or a memory location . Be careful , When the second operand is a memory address , The processor must read the value from memory , Perform the operation , Then write the result back to memory .

Shift operation

Shift operation , The first item first gives the amount of shift , Then the second term gives the number to be shifted ; It is divided into arithmetic shift and logical shift .

The first shift can be an immediate number , Or put it in a single byte register %cl in .( notes ： Only this specific register is allowed as an operand ).

The shift left command has two names :SAL and SHL. The effect is the same , Fill in... On the right 0.

The shift right command is different ,SAR Perform arithmetic shift ( Fill in the sign bit ), and SHR Perform logical shift ( Fill in the 0).

The destination operand of the shift operation can be a register or a memory location .

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