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djpark
Joined: 02 Mar 2004
Posts: 49
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| Help needed: int or int8 doesn't compare < 0 correctly? |
 Posted: Thu Apr 08, 2004 9:02 pm |
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I am desperately seeking help for the code below using PCM 3.188 for 16F648A.
When i becomes negative (-127 ~ -1) I intend to add MAX_INDEX, but that part of the code is not executed and from the asm/list below, it doesn't seem to be compiled in at all.
Am I missing something such as the way how to declare a signed int variable or PCM has a bug?
-- dj
| Code: | #separate
int8 get_index(int t)
{
int8 i;
i = rf_index - t + 1;
if (i < 0)
{
i += MAX_INDEX;
}
return i;
} |
| Code: | 0000 02473 .................... #separate
0000 02474 .................... int8 get_index(int t)
0000 02475 .................... {
0000 02476 .................... int8 i;
0000 02477 ....................
0000 02478 .................... i = rf_index - t + 1;
071B 087E 02479 MOVF 7E,W
071C 0261 02480 SUBWF 61,W
071D 3E01 02481 ADDLW 01
071E 1683 02482 BSF 03.5
071F 00A0 02483 MOVWF 20
0000 02484 .................... if (i < 0)
0000 02485 .................... {
0000 02486 .................... i += MAX_INDEX;
0000 02487 .................... }
0000 02488 .................... return i;
0720 0820 02489 MOVF 20,W
0721 00F8 02490 MOVWF 78
0000 02491 .................... }
0722 1283 02492 BCF 03.5
0723 118A 02493 BCF 0A.3
0724 2F28 02494 GOTO 728 (RETURN)
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Apr 08, 2004 9:33 pm |
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| Quote: | Am I missing something such as the way how to declare a signed
int variable or PCM has a bug? |
The problem is that older versions of the CCS manual had this
vital sentence in them:
| Quote: | All types, except float, by default are unsigned; however,
they may be preceded by 'unsigned' or 'signed'. |
Recent versions do not have it. I have emailed CCS about the
importance of putting that sentence back in, but they haven't
done it yet.
To declare a variable as signed, you have to do this:
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djpark
Joined: 02 Mar 2004
Posts: 49
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| Posted: Thu Apr 08, 2004 9:47 pm |
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| PCM programmer wrote: | | Quote: | All types, except float, by default are unsigned; however,
they may be preceded by 'unsigned' or 'signed'. |
To declare a variable as signed, you have to do this:
|
Thanks a lot for the quick reply.
How strange CCS handles the default. From other C programming experience, I never expected that int default to unsigned int.
Till I got your answer, I had to use bit_test to check the sign bit.
| Code: | //if (i < 0)
if (bit_test(i, 7))
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Now I am back to the normal comparison syntax, thanks to you!
-- dj |
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