Scanf in MIPS assembler language?

Question

I understand the basic functions of MIPS, but I do not understand how to declare variables and especially do not understand how to write the equivalent of scanf()/printf() in MIPS (can't find anything about them online when I search). Here is the code I am trying to translate for now:

#include <stdio>
int main(int argc, char* argv[]) 
{ 
 unsigned long int n; 
 scanf("%d", &n); 
 printf("%lu",fact(n)); 
}

Any guidance?

`#include ` ? It's not MIPS assembler, it's just a C, by the way. — kirilloid, Mar 24 '14 at 23:00
You could try compiling it for mips and looking at the assembly. — Cornstalks, Mar 24 '14 at 23:01
`scanf` itself is a pretty long routine, and uses lots of tables and subroutines. It even [has its own poor man's regex](http://stackoverflow.com/questions/14873542/use-scanf-with-regular-expressions). Writing the same thing in MIPS is an exercise in futility. Since you only want a *number*, try lower level one-character input in a loop. — Jongware, Mar 24 '14 at 23:06
I downloaded spim but don't really know how to write lines of code. — user3251142, Mar 25 '14 at 02:07
If you don't know how to write lines of code, then I think "I understand the basic functions of MIPS" is not an accurate statement. — RobertB, Mar 25 '14 at 02:40
I mean do I need to put it in notepad and like open the file? I don't see where i can click 'new file' — user3251142, Mar 25 '14 at 02:41

score 1 · Answer 1 · answered Mar 25 '14 at 23:31

You are probably looking for the MIPS simulator system calls (syscalls). Here are the SPIM syscalls and the MARS syscalls.

syscall 7 is read double, which is roughly equivalent to scanf("%d", &n)

syscall 1 is print integer, which is equivalent to printf("%u",n)

li   $v0, 1    # service 1 is print integer
move $a0, $t0  # move register to be printed into argument register $a0
syscall

score 0 · Answer 2 · answered Mar 24 '14 at 23:12

You probably do not want to re-implement scanf in assembly. It is much more productive to implement in C or other high-level language. Even better would be to grab an open source implementation, like in glibc.

Here is the source code for scanf() in glibc: http://fossies.org/dox/glibc-2.19/scanf_8c_source.html

Here is a GPL-like implementation: http://mirror.fsf.org/pmon2000/3.x/src/lib/libc/scanf.c

Scanf in MIPS assembler language?

2 Answers2