Chapter 3.7, Problem 3.35PP

A.

Explanation of Solution

Given assembly code:

x in %rdi

rfun:

pushq %rbx

movq %rdi, %rbx

movl $0, %eax

testq %rdi, %rdi

je .L2

shrq $2, %rdi

call rfun

addq %rbx, %rax

.L2:

popq %rbx

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...

B.

Explanation of Solution

Corresponding C code:

// Define method rfun

long rfun(unsigned long x)

{

//If x equals 0

if(x==0)

//Return 0

return 0;

//Assign value after right shit

unsigned long nx = x>>2;

//Call method

long rv = rfun(nx);

//Return value

return x+rv;

}

Explanation:

• The register “%rdi” stores value of “x”.
• The instruction “pushq” stores the data.
• The instruction “movq %rdi, %rbx” saves value of register “%rdi” on “%rbx”.
• The instruction “movl $0, %eax” saves 0 in variable “%eax”.
• The instruction “testq %rdi, %rdi” checks whether value in register “%rdi” is zero.
  • The statement “if(x==0)” is corresponding to C statement...