CS-224 Computer Organization Lecture 08

[@dalalalghomlas1600]

i don't know whats the name of this teacher but if you have ever read this, thank you so much you have no idea how this helped me, you're a great techer.

[@programmerfresco1850]

William Sawyer, Computer Engineer from MIT

[@vibewithsri8064]

its literally 2021 and this man is single-handedly saving my university course...and im from southeast asia on top of that. thank you Prof Sawyer

[@jensmalzer6344]

JEW

[@yadoux]

he's an amazingly clear, interested and interesting teacher.

[@captainbigdaddy5695]

You have changed my life. Thank you

[@olgael7680]

great teacher ever

[@gamar1226]

You still alive?

[@jensmalzer6344]

@@gamar1226 are you still alive?

[@gamar1226]

@@jensmalzer6344 yes, I m taking a shit right now.

[@mhd-em6yt]

the best teacher ever vielen Danke

[@tripplerizz]

this teacher is awsome!!!

[@MoaazElMasry]

I Swear to ALLAH (GOD) you are the best one i had ever seen who explained this topics for me ! Thanks Prof. ALLAH protect you dear.

[@drumdude10]

I think the professor misspoke about the offset. The offset doesn’t add to the value at the address, the offset adds to the address itself.

[@maryihab4324]

This was really helpful .. Thanks a million Prof. =))

[@wristocrat]

guy in the red hoodie is smart

[@OmarKAli-wz5ku]

about the homework in this class, i think that there is no difference between bne & beq in MIPS code that implement the if else statements in higher languages but it just a best practice to make the common case faster , this is my believe at this moment in my current limited knowledge, "والله عليم حكيم "

[@with-jan-mohammad]

yep

[@serdarakol6100]

no i think it is about checking every bit. If you are checking equality you have to check every bit if it is equal. but if you check inequality, in this case getting one inequality in bit will be sufficient. So, you dont have to check every bit. Instructor was asking that I guess..

[@polatsaryerli3071]

I think it might have to do with inner implementation of a comparator. Inequality check uses XOR gates, while Equality is implemented with XNOR, which means it computes the results of XOR anyway, but adds in an additional inverter. I also doubt if it is possible to do an early exit with a hardware operation.

[@avishayguttman6779]

15:32 what's the answer to his question?

[@y09i_]

My guess is they are assuming condition not to be true is more likely, and this way "else" path uses only 2 instructions while "if" path uses 3.

[@jfk-yb2vh]

@@y09i_ No that's not the reason. Look at the answer I've provided in the reply.

[@jfk-yb2vh]

It is because let's say you are comparing 2 32-bit numbers. Now you'd start checking bit by bit for both numbers and see if each bit is equal. If you're checking if the two numbers are not equal, you can immediately return negative as soon as you encounter two non-matching bits. On the other hand if you check if the two numbers are equal, you'd have to iterate over all the 32 bits to determine whether they're equal or not, making the process more time consuming.

[@rahul_terani]

@@jfk-yb2vhsuppose if we use "!=" In high language, then it becomes "be" checking condition in Assembly. As he said. I this case it checks each bit.

[@akin.kilic.]

@@jfk-yb2vh Wow that makes a lot of sense, my first thought was to make it similar in looks to higher level, on higher level if comes first then else, if you do bne first in mips, you are writing the if instructions first and else second, same order as the higher level but your explanation makes a lot more sense.

[@inspired_enough_to_grow_up]

"yani" is that hindi word?

[@thatmanplayzmc1511]

its Turkish and Arabic which means "means"

[@a.n.7338]

can someone tell me why did he used bne condition instead of beq since its in c language???

[@iqbalahmad3754]

for code efficiency, we he used bne . Its a trick to reduce the ambiguity and create simplicity in code.

[@studentcommenter5858]

Because structure of "if" statements from high level languages remains same when changed to assembly level language. if(...){xyz...}else{abc...} is compiled to get bne $r1,$r2, label1 xyz... label2 abc... label1.

[@studentcommenter5858]

This basically comes under MIPs design principle 1 : simplicity favors regularity. They are trying to preserve the structure of the high level program by converting it the way it is to assembly level program.

[@pythonprofreak7522]

In C, we don't have to create a label for the code to jump around based on the condition. Everything is running sequentially and if the condition is met, it will run the specific statement in that condition. If (condition1) else if(condition2) else if (condition3) else .... In MIPS it doesn't have that luxury. If you have two conditions, you can either use the example above by creating just ONE label by using BNE to jump to Exit label or you can create TWO labels. One for BEQ to Loop and One for BNE for EXIT. That is too many things to write and not that efficient as we are using extra memory space. On his example, j Loop is already there to indicates that as long as condition save[i]==k, it will keep looping. That way, we are saving memory space.

[@mech_builder7998]

what's Beechum Sel Dil mean anyone?

[@hanamona5878]

He says "Biçimsel dil" which means "Formal language" in Turkish

[@ericwang4917]

why i is 2 ???????? why i is not 1?? 22:34

[@y09i_]

For every loop iteration we want to calculate the address of save[i] which is 4 * i bytes forward from save[0]. We left shift by 2 to find 4 * i (for example 001 -> 100).

[@pythonprofreak7522]

It is because 4=2^2 which is 4 bytes == 32 bit size of each element in the array. We have to jump 4 bytes on every increment of the i address in the save array.

[@MoaazElMasry]

I Swear to ALLAH (GOD) you are the best one i had ever seen who explained this topics for me ! Thanks Prof. ALLAH protects you dear.