Explain what this fragment of code does instruction by instruction and what purpose it achieves (assuming that register r0 is the register of interest). Note that the data in r0 must not be 0 on entry.
MOV r1,#0
loop MOVS r0,r0,LSL #1
ADDCC r1,r1,#1
BCC loop
This code forms a loop with the MOVS r0,r0, LSL #1 instruction. This instruction shifts the value in r0 one
place left and sets the C?bit (if the bit shifted out was a 1). The S suffix in MOVS, is necessary to allow the C?bit to
be updated. The next instruction, ADDCC r1,r1,#1, is conditionally executed. If the C?bit is clear (the bit
shifted out was not 1) the contents of r1 is incremented.
The final instruction closes the loop. If the C?bit is clear, the loop is repeated. If not, it is cleared. Consequently,
this shifts zeros out of r0, counts them, and stops when a 1 is detected; that is, it counts the number of leading
zeros in a register (e.g., it could be used in normalizing floating?point numbers). Note, if the value in r0 is zero, the
loop will not terminate. You could either create a loop that terminates after 32 cycles or test for zero before
entering this code.
The following shows the execution of the code with dummy data and a means of detecting an all?1s value.
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Answer the following statements true (T) or false (F)
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Without ________, you would not be able to install new hardware on your computer
A) multitasking B) a graphical user interface (GUI) C) device drivers D) an application programming interface (API)
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A. Smart cards B. Fire detectors C. Site selection D. Biometric systems