[PDF] Functions in MIPS - Washington PDF lec05.pdf

— A function can “return” up to two values by placing them in registers $v0-$v1, before returning via jr These conventions are not enforced by the hardware or assembler, but programmers agree to them so functions written by different people can interface with each other

Returning multiple values from a function ▫ Return statement can return only one value ▫ What if we want to return more than one value? ▫ Use pointers 7

[PDF] Functions

Can take in special inputs (arguments) ▷ Can produce an answer value (return value) ▷ Similar to the idea of a function in mathematics With functions, there

[PDF] First-Class Functions in an Imperative World - Luaorg

(They can be passed as arguments, but cannot be returned nor assigned, to avoid escapes ) Modula-2 has both functions as first-class values and lexical scoping,

[PDF] Functions That Return Results, Decision Structures - Rose-Hulman

Functions can take multiple parameters □ def distance (p1, p2): # p1, p2 are points xdist = abs(p1 getX()- p2 getX()) ydist = abs(p1 getY()- p2 getY()) return

[PDF] Functions That Return Results, Decision Structures - Rose-Hulman

Python's can help increase your understanding of what really goes on in a program □ Many other programming languages (notably Java, C++, and C#) derive

[PDF] Assembly Language: Function Calls - Princeton University

0 call instruction pushes return addr (old RIP) onto stack, then jumps RIP ( instruction pointer) register points to next instruction to be executed Note: Can't really

Lecture 5

Announcements:

Today:

³Finish up functions in MIPS

Control flow in C

Invoking a function changes the

control flow of a program twice.

1.Calling the function

2.Returningfrom the function

In this example the mainfunction

calls facttwice, and fact returns twice³but to differentlocations in main.

Each time fact is called, the CPU

has to remember the appropriate return address.

Notice that main itself is also a

function! It is called by the operating system when you run the program. int main() t1 = fact(8); t2 = fact(3); t3 = t1 + t2; int fact(int n) int i, f = 1; for (i = n; i > 1; i--) f = f * i; return f; 3

Function control flow MIPS

MIPS uses the jump-and-link instruction jalto call functions. ³The jal saves the return address (the address of the nextinstruction) in the dedicated register $ra, before jumping to the function. ³jal is the only MIPS instruction that can access the value of the program counter, so it can store the return address PC+4 in $ra. jal Fact To transfer control back to the caller, the function just has to jump to the address that was stored in $ra. jr $ra IHP·V QRR MGG POH ÓMO MQG ÓU LQVPUXŃPLRQV POMP MUH QHŃHVVMU\ IRU RXU factorial example. 4

Data flow in C

Functions accept argumentsand

produce return values.

The blueparts of the program

show the actual and formal arguments of the fact function.

The purpleparts of the code deal

with returning and using a result. int main() t1 =fact(8); t2 =fact(3); t3 = t1 + t2; intfact(int n) int i, f = 1; for (i = n; i > 1; i--) f = f * i; return f; 5

Data flow in MIPS

MIPS uses the following conventions for function arguments and results. argument registers $a0-$a3before calling the function with jal. $v0-$v1, before returning via jr. These conventions are not enforced by the hardware or assembler, but programmers agree to them so functions written by different people can interface with each other. IMPHU RH·OO PMON MNRXP OMQGOLQJ MGGLPLRQMO MUJXPHQPV RU UHPXUQ YMOXHVB 6 Assembly language is untyped³there is no distinction between integers, characters, pointers or other kinds of values. It is up to youPR ´P\SH ŃOHŃNµ \RXU SURJUMPVB HQ SMUPLŃXOMU PMNH VXUH your function arguments and return values are used consistently. For example, what happens if somebody passes the addressof an integer (instead of the integer itself) to the fact function?

A note about types

The big problem so far

There is a big problem here!

³The main code uses $t1to store the result of fact(8).

³But $t1is also used within the fact function!

The subsequent call to fact(3) will overwrite the value of fact(8) that was stored in $t1. 8 A:... 3XP %·V MUJV LQ M0-$a3 jalB# $ra = A2

A2:...

B:... 3XP F·V MUJV LQ M0-$a3, HUMVLQJ %·V MUJVA jalC# $ra = B2

B2:...

jr$ra# Where does # this go??? C:... jr$ra

Nested functions

A similar situation happens when

you call a function that then calls another function. IHP·V VM\ $ ŃMOOV % ROLŃO ŃMOOV FB quotesdbs_dbs21.pdfusesText_27

[PDF] [PDF] Functions in MIPS - Washington