XML CO538 Anonymous Questions and Answers Keyword Index

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Keyword reference for inverting

Question 69 (2000):

In a post, Fred says that the maximum negative 32 bit int is -2147483648, so I have coded appropriately ...

  -- ensure seed is positive & legal
  IF
    seed = (-2147483648)       <---------ERROR!!!
      seed := 2147483647
    seed < 0
      seed := -seed
    seed = 0
      seed := 1
    TRUE
      SKIP

But I get an error on the line arrowed above which says:

          Overflow when evaluating constant expresssion

Help!! Have I done something wrong or is the info on cs2 wrong?

Answer 69:

The compiler treats -2147483648 as an expression, so it gets an error when trying to evaluate 2147483648 (which is larger than the largest INT). If it got past that, it would get another error trying to negate it.

occam has a special way of naming the largest and smallest of any of its number types. For example,

  MOSTNEG INT
  MOSTPOS INT

give you, respectively, the most negative and positive integers. Other ways we can write MOSTNEG INT are:

  #80000000
  1 << 31

But ... my colleague, David Wood, suggests you might like to consider:

  TIMER tim:
  INT seed:
  SEQ
    tim ? seed
    seed := (seed >> 2) + 1

Keywords: inverting , int , random , q7

Referrers: Question 29 (2002)

Question 44 (2000):

I am currently doing the pairs toggling bit of Q4. I am trying to say

  IF there is a toggle input
  THEN switched := NOT switched
  ELSE carry on excuting the rest of the code.

where toggle is an input channel and switched is a boolean variable.

Answer 44:

You are describing a poll on the toggle channel. See slide 5-37 in the notes. You may consider the use of polling absolutely essential (see the comment on slide 5-37) for your solution to this part of the question - even though it's not!

Keywords: q4 , inverting , if

Referrers: Question 47 (2000)

Question 40 (2000):

Is it possible to invert a BOOL variable - for example:

  minus = NOT minus

???

Answer 40:

Yes - but it should be:

  minus := NOT minus

Keywords: inverting