Question

Translate the recursive C function below to a recursive RISC-V procedure.

long long int fun(long long int x, long long int y)

{if (x == 0)

return (y);

else

return(fun(x-1, x+y));}

Write a non-recursive C version of the function from the previous question by eliminating the tail recursion using a goto statement. Then translate to a non-recursive RISC-V version.

Answer 1

Answer 1: Translate to a recursive RISC-V procedure.

c language program: ---------------

long long int fun(long long int x, long long int y)

{if (x == 0)

return (y);

else

return(fun(x-1, x+y));}

RISC-V language program: --------------

_PROCEDURE_LINKAGE_TABLE_:

.#..3..A......C.

.....S......g...

fun(long long, long long):

bnez   a0,10580 <fun(long long, long long)+0x6>

mv a0,a1

ret

addi   sp,sp,-16

sd ra,8(sp)

add    a1,a1,a0

addi   a0,a0,-1

jal    ra,1057a <fun(long long, long long)>

ld ra,8(sp)

addi   sp,sp,16

ret

main:

li a0,0

ret

Answer 2:  translate to a non-recursive RISC-V version.

c language program: ---------------

long long int fun(long long int x, long long int y)

{

    while(true){

        if(x == 0)

            return(y);

    

        x = x - 1;

        y = x + y;

    }

}

RISC-V language program: --------------

_PROCEDURE_LINKAGE_TABLE_:

.#..3..A......C.

.....S......g...

fun(long long, long long):

beqz   a0,10582 <fun(long long, long long)+0x8>

addi   a0,a0,-1

add    a1,a1,a0

bnez   a0,1057c <fun(long long, long long)+0x2>

mv a0,a1

ret

main:

li a0,0

ret