bit field access

[jpc]

using bit field variables i found something strange :

Code: Select all

struct{
  counter : 4;
  status : 3;
  test   : 1;
  } myreg;

...

while(nn<7){
   (x[nn] = nn++);
   myreg.status ++;<<<<<<<<<<<<<<<<<<<<<<<<<<<<
    myreg.counter=myreg.counter+2;}

actually clears counter , add1 to counter and never stores anything in myreg.status.

if i change this to

Code: Select all

while(nn<7){
   (x[nn] = nn++);
   myreg.status = myreg.status + 1;;
    myreg.counter=myreg.counter+2;}

it is ok

[jpc]

it looks as if == reads the value of myreg.status , increments it and then write back as normal byte/word/??? forgetting the offset in the struct
If i init the myreg.status with a value , this value , incremented by one is written in counter , leaving status cleared to zero , on the next pass in this loop myreg.status is read zero , incremented and rewritten to myreg.counter.

[rajkovic]

it looks as if == reads the value of myreg.status , increments it and then write back as normal byte/word/??? forgetting the offset in the struct
If i init the myreg.status with a value , this value , incremented by one is written in counter , leaving status cleared to zero , on the next pass in this loop myreg.status is read zero , incremented and rewritten to myreg.counter.

You are right we have located and fixed bug.