Chapter 4.1, Problem 4.6PP

Explanation of Solution

Given assembly code:

long sum(long *start, long count)

start in %rdi, count in %rsi

sum:

irmovq $8, %r8

irmovq $1, %r9

xorq %rax, %rax     

andq %rsi, %rsi

jmp test

loop:

mrmovq (%rdi),%r10

addq %r10, %rax

addq %r8, %rdi

subq %r9, %rsi

test:

jne loop

ret

Data movement instructions:

• The different instructions are been grouped as “instruction classes”.
• The instructions in a class performs same operation but with different sizes of operand.
• The “Mov” class denotes data movement instructions that copy data from a source location to a destination.
• The class has 4 instructions that includes:
  • movb:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 1 byte data size.
  • movw: 
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 2 bytes data size.
  • movl:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 4 bytes data size.
  • movq:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 8 bytes data size.

Unary and Binary Operations:

• The details of unary operations includes:
  • The single operand functions as both source as well as destination.
  • It can either be a memory location or a register.
  • The instruction “incq” causes 8 byte element on stack top to be incremented.
  • The instruction “decq” causes 8 byte element on stack top to be decremented.
• The details of binary operations includes:
  • The first operand denotes the source.
  • The second operand works as both source as well as destination.
  • The first operand can either be an immediate value, memory location or register.
  • The second operand can either be a register or a memory location.

Jump Instruction:

• The “jump” instruction causes execution to switch to an entirely new position in program.
• The “label” indicates jump destinations in assembly code...