Chapter 7 - Integer Arithmetic

Logical Shift

fills the newly created bit position with zero

Arithmetic Shift

fills newly created bit position with a copy of the number’s sign bit

SHL Instruction

shift left instruction that performs a logical left shift on the destination operand, filling the lowest bit with 0

Fast multiplication

shift left 1 bit (multiplies number by 2)

thus, shifting left n bits multiplies operand by 2^n

SHR Instruction

(shift right) instruction performs a logical right shift on destination operand. Highest bit position filled with a zero

Shifting right n bits divides the operand by 2^n

SAL

Shift arithmetic left (identical to SHL)

SAR

Shift arithmetic right (performs right arithmetic shift on the destination operand)

sign

Arithmetic shift preserves the number’s ____

ROL Instruction

Rotate shifts each bit to the left
Highest bit copied into both Carry flag and lowest bit

No bits are lost

ROR

Rotate right (shifts each bit right)

Lowest bit copied into both carry flag and highest bit

No bits are lost

RCL

Rotate carry left: shifts each bit left

Copies carry flag to least significant bit

Copies most significant bit to the carry flag

RCR

Rotate carry right: shifts each bit to the right

Copies the carry flag to the most significant bit

Copies the least significant bit to the carry flag

MUL Instruction

Unsigned multiply instruction that multiples 8-, 16-, or 32-bit operands by either AL, AX, or EAX

IMUL

Signed integer multiplies an 8-, 16-, 32-bit signed operand by either AL, AX, EAX

Preserves the sign of the product by sign extending it into the upper half of the destination register

DIV

Unsigned instruction that performs 8-, 16-, and 32-bit division on unsigned integers (A single operand is supplied and assumed to be the divisor)

IDIV

Signed integers must be sign-extended before division takes place

CBW, CWD, CDQ Instructions

Provide important sign extension operations

CBW

Convert byte to word (extends AL into AH)

CWD

Convert word to doubleword (extended AX into DX)

CDQ

convert doubleword to quadword (extends EAX into EDX)

IDIV instruction

Signed div performs signed integer divison

ADC Instruction

Add with carry: adds both a source operand and contents of the Carry flag to a destination operand

SBB Instruction

Subtract with borrow: Subtracts both a source operand and the value of the carry flag from a destination operand

BCD

Binary coded decimal integers use 4 binary bits to represent each decimal digit

AAA

ASCII adjust after addition: adjusts binary result of ADD or ADC. Makes result in AL consistent with ASCII decimal representation

AAS Instruction

ASCII adjust after subtraction. Adjusts binary result of SUB or SBB instruction. Makes result in AL consistent with ASCII decimal representation

AAM Instruction

ASCII adjust after multiplication. Adjusts the binary result of a MUL instruction. The multiplication must have been performed on unpacked BCD numbers

AAD Instruction

ACII adjust before division; instruction adjusts the unpacked BCD dvidend in AZ before a division operation

Packed Decimal Integers

store two decimal digit per byte

packed BCD

packed decimal is also known as…

DAA Instruction

Decimal adjust after addition: converts binary result of ADD or ADC operation to packed decimal format

DAS Instruction

Decimal adjust after subtraction: converts binary result of a SUB or SBB operation to packed decimal format (value must be in AL)