NASM Forum > Programming with NASM

Printing of floating point values

(1/2) > >>

andyz74:
Hello people,

my question is, is there any (convenient) possibility to print floating point values, DESPITE printf() ?
I have problem with printf, because using gcc as linker, what I have to do in this case, produces alway error saying the "no-PIE"-stuff.  Do I really have to recompile GCC with the -np-PIE flag to work for me, or is there another possibility to print-out floating point-values?

My system is Debian 12, 64 bit.

Greetings, Andy

Frank Kotler:
Hi Andy,
Welcome to the forum!

I think there should be a way to get gcc to do what you want. Not really a "Nasm question" but you need to know the answer ! , You can print floats without the C library, too but it may not be the best use of your time.

I hope someone can cone up with the right command line to gcc. 

Best,
Frank

andyz74:
Hello Frank, and thanks for the welcome-wishes! :-)

As I think all over it, i just need the printf for "seeing" my values. In fact I do not really need this written out. 
But the printf-function seems to be cabaple of interpreting and displaying the packed BCD-Values.

For example I wrote a piece of code, which calculates different squareroots, which are at least partly even, without floating point. These are moved to registers, where I want to see them with a debugger.  Nevertheless, I can't see my values in the register; I assume, they are BCD-packed, which I assume, printf could write them OR I find another solution. (For unpacking the packed BCD ?)


--- Code: ---; calculates square root

; nasm -f elf64 fpu_sq_root.asm
; ld -s -o fpu_sq_root fpu_sq_root.o


[bits 64]

global _start
 
section .data
    _msg  db '                ',0ah
    len_msg equ $-_msg
    val1: dq 16  ;declare quad word (double precision)
    val2: dq 9  ;declare quad word (double precision)
    val3: dq 4  ;declare quad word (double precision)
    val4: dq 1  ;declare quad word (double precision)
    val5: dq 0  ;declare quad word (double precision)
    val6: dq 0.25  ;declare quad word (double precision)
    val7: dq 2.25  ;declare quad word (double precision)
    val8: dq 6.25  ;declare quad word (double precision)
    val9: dq 12.25  ;declare quad word (double precision)
 
section .bss
    res: resq 1     ;reserve 1 quad word for result
 
section .text
    _start:
    nop
    nop
    nop
    nop
    nop
   
    fld qword [val1] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop

    fld qword [val2] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop

    fld qword [val3] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop

    fld qword [val4] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop

    fld qword [val5] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop

    fld qword [val6] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop
   
    fld qword [val7] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop
   
    fld qword [val8] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop
   
    fld qword [val9] ;load value into st0
    fsqrt           ;compute square root of st0 and store in st0
    fst qword [res] ;store st0 in result
    mov rbx, [res]
    nop
 
nop
nop
nop

mov rax,1
int 80h
    ;end program


--- End code ---

=> Squareroots of the val's are computed and one after each stored in RBX.
If I debug the program with radare2, I see senseless numbers in RBX.
Are they packed BCD? If yes, how to unpack ?

Greetz and thanks, Andy

PS : the many "nop" are for me to be able to get orientation while debugging...

fredericopissarra:
You can separate the integer part from the fractional part with cvttss2si or cvttsd2si, and subtract the original values to get the fractional part (remember to obtain the absolute values). Then, for integer part, you can obtain the # of decimal algarisms using log10, and divide the integer value by 10, in sequence, util you get a zero quotient - getting the actual algarisms... For the fractional part, you just need to multiply them by 10 (until get 0.0 or the # of algarisms you want).

There are faster ways...

andyz74:

--- Quote from: fredericopissarra on October 26, 2023, 06:21:19 PM ---You can separate the integer part from the fractional part with cvttss2si or cvttsd2si, and subtract the original values to get the fractional part (remember to obtain the absolute values). Then, for integer part, you can obtain the # of decimal algarisms using log10, and divide the integer value by 10, in sequence, util you get a zero quotient - getting the actual algarisms... For the fractional part, you just need to multiply them by 10 (until get 0.0 or the # of algarisms you want).

There are faster ways...

--- End quote ---

Ah, many thanks, this is a good way to start! :-)

Navigation

[0] Message Index

[#] Next page