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galatar
Joined: 01 Oct 2008
Posts: 2
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| Mathematical library bug? |
 Posted: Fri Nov 20, 2009 7:21 am |
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I noticed the following strange problem:
Z=Y+X;
X is always nonnegative.
Y is usually 0.0
If presentation of Y is "0x00000000" everything is OK, but if presentation is "0x80000000" something very strange happens.
Z=Y+X = -X ??????
For example:
-0.0 + 88.36 = -88.36
I use PCD compiler Version 4.093 with dsPIC33FG128MC804.
My application used a big data stream from PC and it is very uncomfortable to check every time if value is equal to "0x80000000" and change the presentation to "0x00000000". |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Fri Nov 20, 2009 9:03 am |
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Yes, still present with PCD V4.100.
| Quote: | float x,y,z
x=-0.0;
y=1.0;
z=x+y; |
z gives -1.0 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Nov 20, 2009 1:29 pm |
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It does work OK in the PCM and PCH compilers with vs. 4.100.
Results are:
Test program:
| Code: |
#include <18F452.h>
#fuses XT,NOWDT,PUT,BROWNOUT,NOLVP
#use delay(clock=4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//======================================
int8 main ()
{
float x,y,z;
x=-0.0;
y=1.0;
z=x+y;
printf("%3.2f \n\r", z);
while(1);
} |
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