CS261 - Midterm 2 Flashcards
Elements of an array are next to each other in memory
True
Does A[i] = *(A+i)?
True
C has always supported variable sized multidimensional arrays?
False
How big will int C[5] be if ints are 32 bits?
It will be 20 bytes long.
Assume array long B[10] starts at address x. What address will be B[5] be?
x + 40
Assume the address of int C[5] is in %rdx, and i is in %rcx. What is the address for C[i]?
(%rdx, %rcx, 4)
%rdx = base register of C[5] %rcx = index register i 4 = an integer is 4 bytes, so the scale is going to be 4
Memory Addressing Mode
D(Rb, Ri, S) D = Constant "displacment" of Rb = Base register Ri = Index Register: Any, except for %rsp S = Scale: 1,2,4,8
Assume long A[4][6]. What will the size of A be?
8 * 4 * 6
long = 8 bytes
4 * 6 = 24 cells
Assuming long A[4][6] has base address x. What will the address of A[1][0] be?
x + 6*8
All pointers in C are the same type?
False, like in *p; char *c;
Adding 1 to a pointer will always add 1 byte
False
Pointers can point to functions
True
All pointers are how many bytes?
8
To add 2 operands in y86, the must both be
registers
y86 instructions are all the same size
False, 1-10 bytes
A multiplexor
selects a value from a set of different data values
Registers change value
When the clock signal rises
A single logic gate implements a boolean function in hardware
boolean function
We compute for the value for the next PC in
Fetch
The inputs to the ALU are
Register A and B, or register B and a constant
Whether we read or write during the memory stage, depends on the value of
the code
CPU
• We have the basic components we need to
create a CPU that runs y86 programs
– ALU: Does math/logic
– Registers: Hold values for ALU
– Memory: Holds values over time
– Instruction Memory: Holds instructions
– PC register: Holds pointer to current instruction
Instructions in Stages
Fetch: Read instruction from memory
• Decode: Read operands from the register file
• Execute: ALU performs operations
• Memory: Moves to or from memory are
performed if necessary
• Write Back: Results are saved to register
• PC Update: PC is set to address of next
instruction
FDEMW
What hardware do we need for
decode?
Register file
Decode
Values from register file sent to the ALU
What hardware do we need for
execute?
ALU and condition code registers
