Question

Problem 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. х30, х5, 3 add x30, x10, х30 // x30 %3D &A[F] slli x31, х6, 3 add x31, x11, х31 // х31 %3D &B[g] x5, 0(х30) // x30 = f*8 slli // x31 = g*8 // f = A[f] Id addi x12, х30, 8 х30, 0(x12) add x30, х30, х5 Id 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 xll. • The instruction slli x30, x5, 3 performs 3 positions left shift on the value of x5 and stores the result in x30. This indicates the operation x30=f*8. The instruction add x30, x10, x 30 performs addition operation x30=x10+x30 =&A[0] + f*8 =&A[f] Then, x30 =&A[f] • The instruction slli x31, x6, 3 performs 3 positions left shift on the value of x6 and stores the result in x31. This indicates the operation x31 = g*8. • The instruction add x31, x11, x31 performs addition operation x31=x11+x31 =&B[0] + g*8 =&B[g] Then, x31=&B[g] • The instruction ld x5, 0 (x30) loads the value of array A at index f into the register x5. That means f=A[f] The instruction addi x12, x30, 8 performs addition operation. x12 =x30+8 =&A[f] + 8 =x12 =&A [f+1] The instruction ld x30, 0 (x12) loads the value in register x12 into x30. That is x30 = A[f+1]. The instruction add x30, x30, x5 performs addition operation. x30=x30+x5 = A[f+1] + f = A[f+1] +A[f] • 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 B[g]= A[f+1] +A[f] || Therefore, the equivalent C statement for the given code is B[g]=A[f+1] +A[f].