Nice way to make a limit to the value

Question

I have a code with pixel brightness that is limited to [0..255]. And it's evaluated for some reason, so I can get value outside the bounds. I can do

(if x>maxValue) x = maxValue;

or

 x = min(x, MaxValue);

or

(x > MaxValue) ? MaxValue : x;

but I wonder what is the nice way? How to limit a value with less comparisons and with good code style?

score 2 · Answer 1 · answered Sep 20 '12 at 12:50

2

Use an unsigned char instead of an int for x, chars are limited to [0, 255]. This is a little bit tricky though as you have to check for overflow.

answered Sep 20 '12 at 12:50

Minion91

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Awesome, I liked it. But the other answer is more common. – Pavel Oganesyan Sep 20 '12 at 16:50
It's fairly common to use an unsigned char to represent pixels during image processing. – Science_Fiction Sep 20 '12 at 21:32
I would even go as far as stating that is better to use unsigned chars than anything else for representing them. – Minion91 Sep 21 '12 at 07:30

score 1 · Accepted Answer · answered Sep 20 '12 at 13:13

How to limit a value with less comparisons and with good code style?

One comparison is least, any lesser means there is no comparison. Look at Compute minimum without branching, if you want this.

For good style, this is best -

if (x > maxValue)
{
    x = maxValue;
}

score 0 · Answer 3 · answered Sep 20 '12 at 12:56

inline long clamp(long x, long min, long max){
    return x>max ? max : (x<min ? min : x);
}

You could write a new class that only accepts values between 0 and 255, and can be implicitly casted to an int, but using something like clamp or max should suffice.

Science_Fiction · Answer 4 · 2012-09-20T21:33:17.193

0

I would guess:

(x > MaxValue) ? MaxValue : x;

is equivalent to:

(if x>maxValue) x = maxValue;
else x = x;

I know chances are high that it will get optimized away etc, or stop at self assignment etc. So in essence it is the same as the first if, just syntax sugar coating.

I would use min since it will provide type safety, and help to avoid comparing mixed types.

edited Sep 20 '12 at 21:33

answered Sep 20 '12 at 13:12

Science_Fiction

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score 0 · Answer 5 · 2012-09-20T15:19:33.217

As far as good coding style, you could create your own class to manage this value bounding requirement. If you overload the assignment operator, you could do the comparison there.

Edit: I suppose you could just put all your code in one function instead. But I think interacting with a class instance would be better.

BoundedInt x;
x = 300;
x.value(); // x == 255

Nice way to make a limit to the value

5 Answers5