Binary Arithmetic Flashcards
What is a carry
when we run out of digits for storage, a carry will store the last digit
what is the amount of bits we are limited to in our arm architecture
32
What is the largest number we can represent with 32 bits
2^32
What are the four condition control flags
Negative
Overflow
Zero
Carry
what does the carry flag let us know
that the register does not store the actual answer as it was too big to be stored
how do we tell the processor to update the condition code flags
using s-bit. eg. ADDS, MOVS,
If s bit is set to 0 what does this mean
the condition code fags did not need to be set (false)
If s bit is set to 1 what does this mean
the condition code fags needed to be set (true)
how does the processor remember the results of the compare instruction
by updating the condition code flags
example of everyday modulo arithmetic
12 hour clock
modulo arithmetic used in binary
twos complement
how does twos complement work
the second half of the binary pattern is used again to represent minus numbers. Which way we see it should be from our interpretation of the numbers as the computer doesn’t know whether we are choosing a signed or unsigned interpretation
if the interpretation is negative, what is the most significant bit
1
if the interpretation is positive, what is the most significant bit
0
how to represent a minus number
- get positive version in binary
- invert
- add 1
what does it mean to invert
changing all 0s to 1s and all 1s to 0s
Why does the method we use for changing a binary number to it’s negative version work
inverting the bits is the equivalent of subtracting from minus 1, so that is why we add the 1 on at the end as if we were taking it away from 0
what is the operation used for inverting
MVN
what does MVN stand for
move with not
what operation is used to get the negative version of a number
NEG
what does NEG stand for
negate
what does NEG really do
RSB R0, R0 , #0, when number is stored in r0
technically, why doesnt the processor need to know the method of subtraction
As long as it can do addition and change signs, subtraction can be done
What is oveflow
when the result of addition or subtraction gives a result that is outside of the signed number system
