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convert MCHP float value to regular hex

 
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karth



Joined: 10 Sep 2003
Posts: 29

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convert MCHP float value to regular hex
PostPosted: Tue May 16, 2006 9:10 am     Reply with quote
hey programmers,

I need to know how to convert MCHP float to an hex representation.

example:

1)
float = 2.3
MCHP float representation in HEX = 0x 80 13 64 5A
need to convert = 0x0023

2)
float = 13.5
MCHP float representation in HEX = 801CCCCD
need to convert to = 0x0135

3)
float = 12.0
MCHP float representation in HEX = 82400000
need to convert to 0x0120

Thank you

Embarassed Question
karth



Joined: 10 Sep 2003
Posts: 29

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PostPosted: Tue May 16, 2006 9:56 am     Reply with quote
i do not understand the bit representation of the float 32 bit
could anybody help me
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue May 16, 2006 1:22 pm     Reply with quote
Look in the CCS FAQ, in the Compiler Behavior section. Look at this item:
"What is the format of floating point numbers ?"
http://www.ccsinfo.com/faq.php

Also go here:
http://www.piclist.com/techref/microchip/math/fpconvert.htm
Download floatconv10.zip
Open it with Winzip. Drag floatconv.exe onto your desktop.
Run it. In the Format section, select Microchip 32-bit.
Then you can type in a number and convert it to hex bytes or a float.
Ttelmah
Guest
Re: convert MCHP float value to regular hex
PostPosted: Wed May 17, 2006 5:21 am     Reply with quote
karth wrote:
hey programmers,

I need to know how to convert MCHP float to an hex representation.

example:

1)
float = 2.3
MCHP float representation in HEX = 0x 80 13 64 5A
need to convert = 0x0023

2)
float = 13.5
MCHP float representation in HEX = 801CCCCD
need to convert to = 0x0135

3)
float = 12.0
MCHP float representation in HEX = 82400000
need to convert to 0x0120

Thank you

Embarassed Question


Can I suggest that you don't use float...
The format you are outputting, appears to be what is called 'BCD' (binary coded decimal), with each hex digit, representing a single digit in the decimal result. It is different from the normal BCD format, in being coded in 'tenths', instead of in units.
BCD conversion routines have been posted here many times in the past, and these can simply be used by multiplying the value *10, and storing the result as an integer.
However given that you are dealing with a value that can only be in 'tenths', it is worth asking whether 'float' can be avoided entirely. Integer arithmetic, is vastly faster, and more 'accurate' than FP. The problem is that cumulative errors can appear in floating point sums, which don't exist if the same number is handled in integer. This is why some languages have a 'currency' data type, which uses a scaled integer, instead of a FP value, since when working with money, the rounding/scaling errors associated with FP maths are unacceptable.
If you are not performing any arithmetic that basically requires FP (sin/cos/log etc.), then it might be worth considering working with integer types instead.

Best Wishes
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