Question

2.4 For the RISC-V assembly instructions below, what is the corresponding C statement? Assume that the variables f, g, h, i, and j are assigned to registers x5, x6, x7, x28, and x29, respectively. Assume that the base address of the arrays A and B are in registers x10 and x11, respectively. silix30, x5, 3 // x30=f*8 add x30, x10, x30 // x30=&A [f] s111 x31, x6 , 3 // x31 = g.8 add x31, x11, x31 // x31=&B [g] ld x5, 0(x30) // f=A[f] addi x12, x30, 8 ld x30, 0 (x12) add x30, x30, x5 sd x30, 0 (x31)

Answer 1

Consider the variables f, g, h, i, and j are assigned to registers x5, x6, x7, x28, and x29, respectively. The base address of the arrays A and B are in registers x10 and x11 . The instruction slli x30, x5, 3 performs 3 positions left shift on the value of x5 and stores the result n x30. This indicates the operation x 30-f*8 . The instruction add x30, x10, x30 performs addition operation x30-x10+x30 Then, x30&A [f] The instruction slli x31, 3 performs 3 positions left shift on the value of x6, . x6 and stores the result in x31. This indicates the operation x31g 8 . The instruction add x31, xl1, x31 performs addition operation x31-x11+x31 =&B [0] + g*8 =&B [g] Then, x31 &BIg] . The instruction ld x5, 0 (x30) loads the value of array A at index f into the egister x5. That means f-A[f] . The instruction addi x12, x30, 8 performs addition operation . The instruction ld x30, 0 (x12) loads the value in register x12 into x30. That is x30A[f+1] . The instruction add x30, x30, x5 performs addition operation The instruction sd x30, 0 (x31) performs store operation. Stores the value of register x30 into x31. The register x31 has &B[g]. . Then, the instruction is BIgl AIf+1]+A[f]. Therefore, the equivalent C statement for the given code is B[gl- A[f+1] +A[f