7 bytes incrementally

[Mapo]

Hello everyone,
I have to manage 7 bytes incrementally, starting from a value of 0 up to FF FF FF FF FF FF FF
Do you recommend using 2 DWords or 7 single bytes?
I use an 18F26K22

[John Drew]

An interesting one Mapo.
If it is in an 18F I think it would be simpler to use two DWords. Less tests on overflow.
On the other hand if you use a 16 bit PIC you could use 64 bit integers and just keep incrementing.
John

[shantanu@india]

Can't it be a simple 7-byte array manipulation? You increment the lowest member & when it is equal to 255 you increment the next higher member & set a byte-pointer accordingly.
Initially the array is zero & the byte pointer is also zero. After 255 increments the byte pointer changes from zero to one & the second byte increments from zero to 255. The byte pointer also correspondingly becomes 2 & starts pointing to the third byte in the array & so on.

[tumbleweed]

...when it is equal to 255 you increment the next higher member & set a byte-pointer accordingly.

Not following the whole "byte pointer" thing.

You always increment starting at the lowest byte and any overflow (byte value is now = 0) means you have to increment the next byte too. Repeat for all 8 bytes.

[tumbleweed]

In terms of speed/size, the simplest way would probably be to use dwords...

Code Select Expand

Dim vdw[2] As Dword

Inc vdw[0]
If vdw[0] = 0 Then
  Inc vdw[1]
EndIf
                       


[keytapper]

This may be crazy, like me, but seems to be feasible

Code Select Expand

Device 16F1827
Xtal 32
Dim longVar[8] As Byte
Dim LowDword As Dword At longVar#3
Dim HiDword As Dword At longVar#7

Inc LowDword
If STATUS.0 <> 0 Then
 Inc HiDword
End If
It will consume an extra byte, because of the second Dword 
There are permitted operation on the first LowDword, but must be followed by updating of the syster HiDword, immediately.

[Mapo]

thank you all for the advice, the solution with 2 dwords is simpler and more manageable

[tumbleweed]

This may be crazy, like me, but seems to be feasible

Actually, once you correct the location offsets of the two Dwords that's a pretty good idea!

Code Select Expand

Dim longVar[8] As Byte
Dim LowDword As Dword At longVar#0     ' was Dword At longVar#3
Dim HiDword As Dword At longVar#4      ' was Dword At longVar#7

Inc LowDword
If STATUS.0 <> 0 Then
 Inc HiDword
End If

All this is assuming you can live with an eight-byte array. If not, then you have to do it long-handed with the seven bytes.

[keytapper]

Code Select Expand

Dim LowDword As Dword At longVar#0     ' was Dword At longVar#3

I haven't evaluated the Dword size starting from right to left order. I just looked at the assembler code that gave me what I supposed was my concept.
In facts the operation in assembler would use a chain of contiguous memory, as long as the carry is propagated to the highest byte of the addition. But to use in basic formulation, I whipped it out like that.

All this is assuming you can live with an eight-byte array

That's the best tradeoff.