4.4 Bit Manipulation Instructions Shift instructions: SHL/SAL, SHR, SAR Examples: initial value in AX= 0110111100000001B CF=0 SAL AX,1 AX=1101111000000010B lost AX=1111110111100000B SAR AX,4 CF=0 Shift instructions: SHLD, SHRD Examples: CX=0BC3H; AX= 5678H SHRD AX,CX,4 CF=1 CX=0BC3H; AX= 3567H unchanged

4.4 Bit Manipulation Instructions Rotate instructions: ROL, ROR, RCL, RCR Examples: initial value in AX= 0110111100000001B CF=0 ROL AX,1 AX=1101111000000010B AX=0010110111100000B ROR AX,4 CF=0 Examples: initial value in AX= 0110111100000001B and CF=1 RCL AX,1 AX=1101111000000011B CF= 0 AX=0110110111100000B CF=0 RCR AX,4

4.5 Program Transfer Instructions JMP Short jump address is computed adding the signed byte operand to the address of the first byte following the JMP instruction. LOOP, LOOPE/LOOPZ, LOOPNE/LOOPNZ JCXZ, JECXZ

4.5 Program Transfer Instructions Jcc The terms “less” and “greater” are used for comparisons of signed integers. The terms “above” and “below” are used for comparisons of unsigned integers.

4.5 Program Transfer Instructions CALL … 0100 CALL EXSUB 0103 ADD AX, 1 0204 CALL EXSUB 0207 ADD AX,2 RET … 0500 EXSUB PROC NEAR ... 0550 RET EXSUB ENDP Assembler directives specifying the begin and the end of a NEAR or FAR procedure (subroutine) Stack: 1FFE ?? 1FFF ?? 2000 ?? Stack: 1FFE 07 1FFF 02 2000 ?? Stack: 1FFE 03 1FFF 01 2000 ?? SP SP SP SP SP

4.5 Program Transfer Instructions INT … 0000:0084 B4 0000:0085 16 0000:0086 26 0000:0087 07 IPT= Interrupt Pointer Table 4*21H=84H IRET,IRETD … 0100:00FF MOV AH, 2CH; 0100:0101 INT 21H 0100:0103 ADD AX, 1 … 0726:16B4 ISR for INT 21 ... … IRET INTO,BOUND Stack: 1FFA ?? 1FFB ?? 1FFC ?? 1FFD ?? 1FFE ?? 1FFF ?? 2000 ?? Stack: 1FFA 03 1FFB 01 1FFC 00 1FFD 01 1FFE 08 1FFF 41 2000 ?? SP SP SP FLAGS=4108H

4.5 Program Transfer Instructions ENTER, LEAVE ENTER 6,0 … 00F8 ?? 00F9 ?? 00FA ?? 00FB ?? 00FC ?? 00FD ?? 00FE ?? 00FF ?? 0100 ?? … 00F8 ?? 00F9 ?? 00FA ?? 00FB ?? 00FC ?? 00FD ?? 00FE 34 00FF 12 0100 ?? SP SP BP SP If Level=0, BP is saved on stack, BP is loaded with the content of SP, Reserved memory space SP is decremented by Space16. BP old value =1234H SP old value =0100H BP new value =00FEH SP intermediate value =00FEH SP final value =00F8H LEAVE SP is loaded with the content of BP, BP is popped from stack.=> values before ENTER restored. Stack Frame Frame pointer SP back to old value =0100H BP back to old value =1234H

4.6 Processor Control Instructions