C$-$Style String Length

The strlen function in $C$ calculates the length of a $C$ string: a sequence of bytes that's terminated by a null byte $(\frac{1}{\frac{?}{?}}0\text{'}).$ Write an

assembly function strlen$\_$mine in lab$6.$ S that does this: takes a pointer to a byte array and counts the number of bytes before getting

to a null $($zero$)$ byte.

Remember that we're working with bytes here $($not $64-$bit values$),$ and that if you have a memory address $($pointer$)$ in a register, you can

follow the pointer to inspect that memory location by putting the register name in parenthesis. i$.$e$.$ this is probably a useful comparison to

make $($adjusting the register name as you like$)$:

cmpb $$0,(\%$rdi$)$

The provided tests. c contains some tests of this and the next function. It #includes the data from test$\_$strings.c as test cases.

The test$\_$strings.c does not need to be included on the command line:

gcc $-$Wall $-$Wpedantic $-$std$=$c$17-$march$=$haswell $-03$ tests.c lab$6.$S $\}$

&&$./$a$.$out

UTF$-8$ String Length

C strings are not typically treated like encoded Unicode characters, but they could be$.$ Write an assembly function strlen$\_$ut $f8$ in

lab$6.$ S that calculates the number of Unicode characters in a byte array, treating it as UTF$-8-$encoded text.

This will be similar to the previous question, except you should not count bytes that are UTF$-8$ continuation bytes: any byte in the form

$10$xxxxxx is a continuation byte. You will need to extract those specific bits from each byte to see if they are the "right" value for a

continuation byte.

If you want to examine specific bits of an integer, you can construct a value to bitwise$-$AND with to keep exactly the bits you care about. In

this case, $11000000$ :

$0$bxxyyyyyy

& $0$b$11000000$

$=0bx000000$

And then make a comparison for equality. WRITE ASSEMBLY CODE FOR THIS FUNCTION!!!!!!!!! IT SHOULD PASS THE TESTS.C WHICH IS ALSO PROVIDED