Quiz on Textbook Sections 2.1 to 2.8

Q1: What C statement is represented by the following RISC-V assembly code?

add  x5, x8, x9
add  x6, x20, x11
sub  x8, x5, x6
Solution: a = (a + b) - (c + d);

Q2: Which of the following RISC-V instruction implements the C assignment

n = A[3];

assuming n is in x9, the base address of A is in x10, and A is an array of uint64_t?
Solution: ld  x9, 24(x10)

Q3: The statement that RISC-V is little-endian means that the least-significant byte of a doubleword in memory is at the lowest address and the most-significant byte the doubleword is at the highest address. 
Solution: True

Q4: What range of values can be used as the immediate operand in a RISC-V addi instruction? 
Solution:  −2048 to +2047
 
Q5: What RISC-V instruction is encode by the hexadecimal word 04533023? 
Solution:  sd  x5, 0x040(x6)

Q6: If the register x8 contains the value 0x804600B91200C00F, what value is placed in x5 by the instruction

srli x5, x8, 4
Solution: 0x0804600B91200C00


Q7: What C statement is implemented by the following RISC-V assembly code, assuming a is in x9 and b is in x18?

    blt  x18, x9, L1
    addi x9, x9, 1
L1:
Solution: if (a <= b) a = a + 1;


Q8: Which of the RISC-V code sequences correctly implements the C statements

i = 0;
while (A[i] != 0) i++;

assuming i is in x9 and the address of A is in x18
Solution:

    addi x9, x0, 0
L1: slli x5, x9, 3
    add  x5, x5, x18
    ld   x5, 0(x5)
    beq  x5, x0, L2
    addi x9, x9, 1
    j    L1
L2:

Q10: The RISC-V calling convention uses registers x10 to x17 for parameter passing. If a procedure has more than eight parameters, where are the additional parameters passed? 
 Solution:
They are pushed onto the stack by the caller.