Divide by 6 using C and avoiding floating point? - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 27th March 2008, 12:29 AM

I'm doing a dice program using a freerunning timer that automatically and fairly counts from 0-6^x (where x is number of die)
Now one die is easy (I'm a BASIC programmer but want to do it in C18)

So
A single die is roll+1

Two dice are D1=int(roll/6)+1 and D2=(roll mod 6)+1

Any ideas on 3 or more dice? And avoiding floating point...

Pommie · 27th March 2008, 01:25 AM

Isn't it just

D1=roll mod 6
D2=(roll/6) mod 6
D3=(roll/36) mod 6
D4=(roll/216) mod 6
etc.

If you do it in integer maths then it should just work.

Mike.

blueroomelectronics · 27th March 2008, 03:20 AM

There you go, thanks I just couldn't see the forest for the trees.

Hero999 · 27th March 2008, 11:44 AM

Does the MCU you're using have a hardware divide instruction or are you useing a maths library?

The x86 does and puts the quotent and remainder in to different registers. Using a high level language like C will probably end up producing two divide instructions, one to get the remainder and another for the quotent which is a wate of clock cycles. I'd recommend doing the division part in assembler, that way you can use one instruction to get both the quotent and remainder.

Pommie · 27th March 2008, 02:11 PM

Quote:

Originally Posted by Hero999

Does the MCU you're using have a hardware divide instruction or are you useing a maths library?

The x86 does and puts the quotent and remainder in to different registers. Using a high level language like C will probably end up producing two divide instructions, one to get the remainder and another for the quotent which is a wate of clock cycles. I'd recommend doing the division part in assembler, that way you can use one instruction to get both the quotent and remainder.

What use is the remainder? For D4 the calculation goes, int(roll/216), result/6 and keep remainder. Two divides required anyway. D2 is the only one that could benefit from the remainder but the additional code wouldn't be worth it.

Mike.

Hero999 · 27th March 2008, 04:52 PM

I don't see why more than one divider per iteration is required.

Roll is the variable with the the value generated by the timer.

Divide, is the divide instruction, it accepts two variables, the first value is divided by the second value. After the instruction is executed the quotent is stored in the first variable and the remainder is stored in the second.

e.g.

x = 105
y = 10
Divide x, y
Print x, y

The output will be:
10 5

Assuming the PIC has a similar instruction, here's how you'd use it. Roll is the random number which is set before the code runs.

Do
Remainder = 6
Divide Roll, Remainder
Print Remainder
Loop until Roll = 0

blueroomelectronics · 27th March 2008, 09:13 PM

Well the formula should work well as an unsigned int function (now I'll have to learn C18 functions)

Code:

for Roll = 0 to 6^4-1
D1 = int(Roll/1 mod 6)+1
D2 = int(Roll/6 mod 6)+1
D3 = int(Roll/36 mod 6)+1
D4 = int(Roll/216 mod 6)+1
print Roll, D1, D2, D3, D4
next

Just BASIC program

Pommie · 27th March 2008, 11:05 PM

Hero,
I see what you mean now. Doing it in asm would save a divide.

Bill,
In C it would simply be,

Code:

    D2=((Roll/6)%6)+1;

Not much difference really.

Mike.

blueroomelectronics · 27th March 2008, 11:16 PM

Thanks I always thought % meant binary. But in C it means modulo.

Using special mode the CCP allows TMR1 to be a free running modulo x counter.

**3v0** · 27th March 2008, 11:45 PM

0xAA = 0b10101010

Pommie · 27th March 2008, 11:51 PM

Quote:

Originally Posted by blueroomelectronics

Using special mode the CCP allows TMR1 to be a free running modulo x counter.

Ahh, the special event trigger, one of my favourites.

Mike.

blueroomelectronics · 28th March 2008, 01:37 AM

Quote:

Originally Posted by Pommie

Ahh, the special event trigger, one of my favourites.

Mike.

It's a real gem, it was one of your older posts that pointed it out to me.

It occurred to me to let it free run till you press a button, presto instant random number.
I could do the software in Swordfish easy, but it's more a challenge to do it in C18.

Eventually I'll make a Risk game battle dice (5 dice) roller on the Junebug as one of the tutorials.

petrv · 8th April 2008, 06:25 AM

You can of course use the compiler's runtime library to do the division if the PIC does not have a hardware divider, but if it is just for 2 dice why don't you use repeated substraction in a loop ? Stupid ,yes but very simple and performance is not a concern in this case, anyway the number of iterations would be 0 to 5 so who cares ? This will give you both the result of the division and the remainder... easy to do even in assembly.
Petr

27th March 2008, 12:29 AM	(permalink)
blueroomelectronics Experienced Member Blog Entries: 4	Divide by 6 using C and avoiding floating point? I'm doing a dice program using a freerunning timer that automatically and fairly counts from 0-6^x (where x is number of die) Now one die is easy (I'm a BASIC programmer but want to do it in C18) So A single die is roll+1 Two dice are D1=int(roll/6)+1 and D2=(roll mod 6)+1 Any ideas on 3 or more dice? And avoiding floating point... __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

27th March 2008, 03:20 AM	(permalink)
blueroomelectronics Experienced Member Blog Entries: 4	There you go, thanks I just couldn't see the forest for the trees. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

27th March 2008, 11:44 AM	(permalink)
Hero999 Experienced Member	Does the MCU you're using have a hardware divide instruction or are you useing a maths library? The x86 does and puts the quotent and remainder in to different registers. Using a high level language like C will probably end up producing two divide instructions, one to get the remainder and another for the quotent which is a wate of clock cycles. I'd recommend doing the division part in assembler, that way you can use one instruction to get both the quotent and remainder. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

27th March 2008, 04:52 PM	(permalink)
Hero999 Experienced Member	I don't see why more than one divider per iteration is required. Roll is the variable with the the value generated by the timer. Divide, is the divide instruction, it accepts two variables, the first value is divided by the second value. After the instruction is executed the quotent is stored in the first variable and the remainder is stored in the second. e.g. x = 105 y = 10 Divide x, y Print x, y The output will be: 10 5 Assuming the PIC has a similar instruction, here's how you'd use it. Roll is the random number which is set before the code runs. Do Remainder = 6 Divide Roll, Remainder Print Remainder Loop until Roll = 0 __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

27th March 2008, 09:13 PM	(permalink)
blueroomelectronics Experienced Member Blog Entries: 4	Well the formula should work well as an unsigned int function (now I'll have to learn C18 functions) Code: for Roll = 0 to 6^4-1 D1 = int(Roll/1 mod 6)+1 D2 = int(Roll/6 mod 6)+1 D3 = int(Roll/36 mod 6)+1 D4 = int(Roll/216 mod 6)+1 print Roll, D1, D2, D3, D4 next Just BASIC program __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

27th March 2008, 01:25 AM	(permalink)
Pommie Experienced Member	Isn't it just D1=roll mod 6 D2=(roll/6) mod 6 D3=(roll/36) mod 6 D4=(roll/216) mod 6 etc. If you do it in integer maths then it should just work. Mike.

27th March 2008, 11:05 PM	(permalink)
Pommie Experienced Member	Hero, I see what you mean now. Doing it in asm would save a divide. Bill, In C it would simply be, Code: D2=((Roll/6)%6)+1; Not much difference really. Mike.

27th March 2008, 11:16 PM	(permalink)
blueroomelectronics Experienced Member Blog Entries: 4	Thanks I always thought % meant binary. But in C it means modulo. Using special mode the CCP allows TMR1 to be a free running modulo x counter. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com Last edited by blueroomelectronics; 27th March 2008 at 11:20 PM.

27th March 2008, 11:45 PM	(permalink)
3v0 Moderator Blog Entries: 3	0xAA = 0b10101010 __________________ search engine for electronic parts Junebug USB PIC programmer kit. USB Bit Wacker

8th April 2008, 06:25 AM	(permalink)
petrv Experienced Member	You can of course use the compiler's runtime library to do the division if the PIC does not have a hardware divider, but if it is just for 2 dice why don't you use repeated substraction in a loop ? Stupid ,yes but very simple and performance is not a concern in this case, anyway the number of iterations would be 0 to 5 so who cares ? This will give you both the result of the division and the remainder... easy to do even in assembly. Petr

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