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roccat
Joined: 13 Jan 2013
Posts: 8
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| multiplication problem |
 Posted: Sun Jun 09, 2013 9:09 am |
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Hello. I'm using 5.005 demo. dspic33ep64gp504
| Code: | char a,b;
a=1;
b=a*3; |
After multiplying b = 6, and should be 3. Why is that?
asm list:
| Code: |
231: a=1;
0806 B3C010 mov.b #0x1,0x0000
0808 B7F048 mov.b 0x0000,0x1048
232: b=a*3;
080A BFD048 mov.b 0x1048,0x0000
080C FB0000 se 0x0000,0x0000
080E 780200 mov.w 0x0000,0x0008
0810 B82063 mul.uu 0x0008,#3,0x0000
0812 B7F047 mov.b 0x0000,0x1047
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z3ngew
Joined: 20 Apr 2013
Posts: 50
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| Posted: Sun Jun 09, 2013 9:21 am |
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try this
| Code: | int a,b;
a = 1;
b = a * 3; |
change data type to int
Good Luck,
z3ngew |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Sun Jun 09, 2013 9:42 am |
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| Where do you see the result of 6? The result of the shown assembly code will be 3. |
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roccat
Joined: 13 Jan 2013
Posts: 8
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| Posted: Sun Jun 09, 2013 9:42 am |
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It did not help. Anyway 6.
If a = 2, after multiplication b=12.
| Code: | 231: a = 2;
079C 200024 mov.w #0x2,0x0008
079E 888544 mov.w 0x0008,0x10a8
232: b = a * 3;
07A0 808544 mov.w 0x10a8,0x0008
07A2 B82063 mul.uu 0x0008,#3,0x0000
07A4 888550 mov.w 0x0000,0x10aa |
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roccat
Joined: 13 Jan 2013
Posts: 8
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| Posted: Sun Jun 09, 2013 9:48 am |
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| FvM wrote: | | Where do you see the result of 6? The result of the shown assembly code will be 3. |
mplab -> mplab sim -> watch.
I checked on pic16f913, the result was 3. on this chip result 6. |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Sun Jun 09, 2013 11:50 pm |
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The strange result can be traced down to
| Code: | | 0220 B82063 mul.uu 0x0008,#3,0x0000 |
Apparently a MPLAB SIM bug. The same instruction is shown with correct result for other 16-Bit PICs. |
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