Weird Quirk with ITOA

alexanbo

Was doing some troubleshooting on a CRC calculation and noticed that when I used ITOA to show some data it gave me some odd results

button_event[10128:1:0,1]
{
   push:
   {
      stack_var integer crc
      crc = $ffff
      send_string 0,"'Test 1:',itoa(crc << 8)"
      send_string 0,"'Test 2:',itoa(crc + 1)"
   }
}

Returned:
Test 1:16776960
Test 2:0

Which is odd because I expected Test 1 to be $FF00 not $FFFF00. In digging I found that ITOA's parameter is actually a Long which kinda explains the first result, but then it's not consistent with the second result?

Joe Hebert

If you change:
send_string 0,"'Test 1:',itoa(crc << 8)"

To this equivalent:
send_string 0,"'Test 1:',itoa(crc * 256)"

Then you get the expected result of 65280 ($FF00)

Weird indeed.

alexanbo wrote: »

Was doing some troubleshooting on a CRC calculation and noticed that when I used ITOA to show some data it gave me some odd results

button_event[10128:1:0,1]
{
   push:
   {
      stack_var integer crc
      crc = $ffff
      send_string 0,"'Test 1:',itoa(crc << 8)"
      send_string 0,"'Test 2:',itoa(crc + 1)"
   }
}

Returned:
Test 1:16776960
Test 2:0

Which is odd because I expected Test 1 to be $FF00 not $FFFF00. In digging I found that ITOA's parameter is actually a Long which kinda explains the first result, but then it's not consistent with the second result?

mpullin

It might be an odd behavior of the bitwise shove (<<) as opposed to itoa. What happens if you remove itoa and just print the numbers?

alexanbo

I think it is in itoa, because the calcuation was actually being done correctly, just when I tried to print out intemediary values with itoa that it got funky, sort of a Schr?dinger's Cat sort of thing.

For example if you added a line before the print statement
crc = $ffff << 8

and changed the print statement to:
send_string 0,"'Test1:',itoa(crc)"

it would print out the $ff00 decimal equivalent

jweather

alexanbo wrote: »

I think it is in itoa, because the calcuation was actually being done correctly, just when I tried to print out intemediary values with itoa that it got funky, sort of a Schr?dinger's Cat sort of thing.

For example if you added a line before the print statement
crc = $ffff << 8

and changed the print statement to:
send_string 0,"'Test1:',itoa(crc)"

it would print out the $ff00 decimal equivalent

Yes, because crc is an integer (16 bits).

If you said

STACK_VAR LONG_INTEGER test
test = $ffff << 8 // or test = $ffff * 256

then the result is $ffff00, because test is a 32-bit integer.

It's nothing to do with itoa aside from the fact that its argument is a LONG_INTEGER. The $ffff+1 test may be running into some weird signed/unsigned arithmetic as well.