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butterfly
Joined: 04 Jun 2006
Posts: 35
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| some div problem |
 Posted: Wed Sep 06, 2006 4:43 am |
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i'm using pic16f877a. And want to do:
i have signed integer and value;for example;
int16 value,result;
int16 zerovalue=0x01f0;
int8 step=0x03;
value = Read_ADC();
value=value-zerovalue;//// i want to learn if it is negatif
result=div(step,value);
whatever value negatif or pozitif, is result pozitif?
i could not understand that
wuold you mind giving me hand? |
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Ttelmah
Guest
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| Posted: Wed Sep 06, 2006 7:24 am |
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You do not have a 'signed integer'. Your declaration of the integers, is using the _unsigned_ type. This is the default. So if (for instance), you have a value of '0x100', and then perform the subtraction 0x100-0x1F0, you will 'get' the positive result 65296, The arithmetic has 'wrapped', but cannot represent the negative value (since the integers are unsigned), so you get the result + 65536...
Use signed values:
| Code: |
signed int16 value,result;
signed int16 zerovalue=0x01f0;
int8 step=0x03;
value = Read_ADC();
value=value-zerovalue;//// i want to learn if it is negatif
//It now will be negative, since the data type is signed.
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There is also though a 'caveat' your division, is performing int8 arithmetic, using an int8, and an int16 value. The 'div' function, also does not expect a int16 result declaration, but a div_t result declaration, to contain both the quotient, and remainder. At present, you are dviding '3', by a value that is almost certainly much larger, so will get a garbage return...
Best Wishes |
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