Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472

Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /home/jerdew5/orbworks.com/forum/includes/bbcode.php on line 472
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 3368: Cannot modify header information - headers already sent by (output started at /includes/bbcode.php:472)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 3370: Cannot modify header information - headers already sent by (output started at /includes/bbcode.php:472)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 3371: Cannot modify header information - headers already sent by (output started at /includes/bbcode.php:472)
[phpBB Debug] PHP Notice: in file /includes/functions.php on line 3372: Cannot modify header information - headers already sent by (output started at /includes/bbcode.php:472)
OrbWorks Community Forum • View topic - Simple (?) Checksum question

Simple (?) Checksum question

Postby jasman on Thu Oct 31, 2002 4:20 pm

Hi - I'm a newbie to PocketC and so far I'm pretty impressed. I need a little help with a bit of code though...

I'm reading a 10 byte sample through the serial port (using serrecva())- first 8 bytes are data, 9th byte is a 'checksum' and final byte is an incremental counter.

The checksum in this case is simply a sum of the 8 data bytes, then cut down to 8 bits in length.

Question is....
Is there a 'cheap' way of doing that? My initial thoughts are (sharp intake of breath) add up the 8 bytes, convert to hex, then convert the hex to a string, and extract the last two characters. Then compare this with the 'received' checksum (converted to a string) and... hey presto!

I haven't actually received the hardware to pump out the 10 byte sample yet so I can't test this theory - this is more of a preemptive strike.

Your thoughts would be appreciated,

jasman
jasman
 
Posts: 4
Joined: Thu Oct 31, 2002 4:03 pm
Location: United Kingdom

Postby Rory Davis on Thu Oct 31, 2002 5:01 pm

// a[0]... a[7] is data

int counter = 7;
int sum;
int packetvalid;

while(counter--){
sum = sum + a[counter]; // add the contents together
}
sum = sum & 0xff; // mask off more than 8 bits

if(sum == a:?:) packetvalid = 1; // good packet
else packetvalid = 0;

Rory
Rory Davis
 
Posts: 37
Joined: Wed Oct 02, 2002 1:32 am
Location: USA

Postby jasman on Fri Nov 01, 2002 7:08 am

Thanks Rory!
It was the

sum = sum & 0xff; // mask off more than 8 bits

that I was missing.

jasman.
jasman
 
Posts: 4
Joined: Thu Oct 31, 2002 4:03 pm
Location: United Kingdom


Return to PocketC for Palm OS KB

Who is online

Users browsing this forum: No registered users and 2 guests

cron