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hex to float

 
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andreluizeng



Joined: 04 Apr 2006
Posts: 117
Location: Brasil

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hex to float
PostPosted: Wed Feb 06, 2008 11:24 am     Reply with quote
Hi people, Im having some problem with data conversion...

I have to convert 4 byte data to a float, but something strange is happening.

for example the following value:

Code:

//FLOAT

0,0328285

0x3D

0x06

0x77

0x39



using the same float value on this code:

Code:

   x = 0.0328285;      

   printf ("\r\nValue: %.7f", x);
   buf[0] = *((int8 *)&x + 0);
   buf[1] = *((int8 *)&x + 1);
   buf[2] = *((int8 *)&x + 2);
   buf[3] = *((int8 *)&x + 3);


   printf ("\r\nhexa: %x %x %x %x", buf[0],  buf[1],  buf[2],  buf[3]);
   *(int8 *)&y = buf[0];
   *((int8 *)&y +1) = buf[1];
   *((int8 *)&y +2) = buf[2];
   *((int8 *)&y +3) = buf[3];


   printf ("\r\nfloat: %.7f", y);



the result is:

Code:

Value: 0.0328285
hexa: 7a 06 77 2d
float: 0.0328285


the original value is a float converted using labview and sent throught UART.

anyone can help ?


regards.
_________________
Andre
Ttelmah
Guest
PostPosted: Wed Feb 06, 2008 11:37 am     Reply with quote
I'd suspect without looking at the values, that this is the classic IEEE versus CCS/Microchip float problem.
The CCS compiler, uses a float format first used in a Microchip application note, which makes it slightly easier on the PIC to handle the data. However the order of the bits in the byte, is _not_ the same as used in the IEEE standard, which is what is normally used in a PC.
If your compiler is reasonably 'recent' (any time in the last couple of years), look at the 'ieeefloat.c' file in the drivers directory. It contains code to convert the numbers in both directions.
If your compiler predates this, I have posted routines to do this here some time ago, and a search should find them.

Best Wishes
andreluizeng



Joined: 04 Apr 2006
Posts: 117
Location: Brasil

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PostPosted: Wed Feb 06, 2008 1:51 pm     Reply with quote
Ttelmah,

i used those function, and it works....

thanks.

regards.
_________________
Andre
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