Write a function (subroutine) that inputs a data value in register r0 and returns value in r0. The function returns y = a + bx + cx2 where a, b, c are parameters built into the function (i.e., they are not passed to it). The subroutine also performs clipping. If the output is greater than a value d, it is constrained to d (clipped). The input in r0 is a positive binary value in the range 0 to 0xFF. Apart from r0, no other registers may be modified by this subroutine.
What will be an ideal response?
The following code provides a subroutine (we’ve built in the constants). Following that is the output of a simulation run.
Sub STMFD sp!,{r1,r2,r14} ;save working registers and link register
MUL r1,r0,r0 ;square x
MOV r2,#2 ;c = 2
MUL r1,r2,r1 ;cx2
MOV r2,#3 ;b = 3
MUL r0,r2,r0 ;bx (note r0 overwritten)
ADD r0,r0,r1 ;cx2 + bx
ADD r0,r0,#4 ;cx2 + bx + a
CMP r0,#200 ;above the limit?
MOVGT r0,#200 ;if so ? clamp
LDMFD sp!,{r1,r2,pc} ;restore registers and copy link to pc to return
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