how can do float multiplication in assembly?

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I want to write this code:

C++

y= 0.4*x+1

but I have some errors in MIPS assembly

[Edit - Added from comment]
I have an integer value in register $t1 and I want to multiply it with 0.4 but it has error in the second line:

assembler

li.s $f0, 0.4
mul.d $f1, $f0, $t1
mfhi $a2
mflo $v0

# print the result
li $v0, 2 # load appropriate system call code into reg $v0
la $a0, 0($v0) # load address of string to be printed on $a0
syscal

[/Edit]

Posted 30-Oct-15 1:20am

amin.j

Updated 30-Oct-15 2:03am

phil.o

v2

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phil.o 30-Oct-15 7:22am

Which errors?

amin.j 30-Oct-15 7:33am

I have an integer value in register $t1 and I want to multiply it with 0.4 but it has error in the second line:

li.s $f0, 0.4
mul.d $f1, $f0, $t1
mfhi $a2
mflo $v0

# print the result
li $v0, 2 # load appropriate system call code into reg $v0
la $a0, 0($v0) # load address of string to be printed on $a0
syscal

Jochen Arndt 30-Oct-15 8:18am

Even for those who know MIPS assembler (I don't), it would be helpful to know the error message.

Not knowing the assembler or starting with it, I would lookup the mul.d instruction and check if the arguments are correct (here especially if an integer register is allowed as third argument).

Philippe Mori 30-Oct-15 13:47pm

Write equivalent code in C or similar language. Compile the code and look at the disassembly...

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CPallini · Answer 1 · 2015-10-30T02:38:00

Solution 1

Quote:
mul.d $f1, $f0, $t1

I guess you have to use a floating point (FPU) register (instead of $t1) as target.

Posted 30-Oct-15 2:38am

CPallini

Comments

ridoy 30-Oct-15 9:01am

yes, thats the point.

amin.j 30-Oct-15 10:25am

As I know:

mul.d $destination, $source, $source

the third one is the second float pint for multiplying. But, my case is different, I want to multiply one integer in $t1 with a float in $f0; how can I do that?

Jochen Arndt 30-Oct-15 13:32pm

You must convert the integer to a floating point and pass the destination register of the conversion to the multiply function.