Chapter 3.6, Problem 3.31PP

Explanation of Solution

Given assembly code:

switcher:

cmpq $7, %rdi

ja .L2

jmp *.L4(,%rdi,8)

.section .rodata

.L7:

xorq $15, %rsi

movq %rsi, %rdx

.L3:

leaq 112(%rdx), %rdi

jmp .L6

.L5:

leaq (%rdx, %rsi), %rdi

salq $2, %rdi

jmp .L6

.L2:

movq %rsi, %rdi

.L6:

movq %rdi, (%rcx)

ret

Explanation:

• The registers “%rsi”, “%rdi”, “%rdx” and “%rcx” contains values for “a”, “b”, “c” and “d” respectively.
• The details of given assembly code is shown below:
  • The instruction “cmpq $7, %rdi” compares value of register “%rdi” with value 7.
  • The instruction “ja .L2” jumps to label “.L2” if value is above.
  • The instruction “.L4(,%rdi,8)” checks jump table and performs operation “movq %rsi, %rdi”.
  • The instruction “xorq $15, %rsi” performs “xor” operation of register “%rsi” with 15.
  • The instruction “movq %rsi, %rdx” moves value of register “%rsi” to register “%rdx”.
  • The instruction “leaq 112(%rdx), %rdi” performs operation “112 + c” and stores in “%rdi” register.
  • The instruction “salq $2, %rdi” performs shift left operation with register “%rdi”.
  • The instruction “jmp .L6” jumps to label “.L6”.
  • The instruction “movq %rsi, %rdi” moves value of register “%rsi” to register “%rdi”.
  • The instruction “movq %rdi, (%rcx)” moves value of register “%rdi” to location of register “%rcx”.

switch statement:

• A “switch” statement provides branching capability in multiple ways based on index that is an integer.
• It is useful in cases where large number of possible outcomes may occur.
• The “jump table” allows efficient implementation of code...