How can I write a 'clamp' / 'clip' / 'bound' macro for returning a value in a given range?

Question

I often find myself writing something like

int computedValue = ...;
return MAX(0, MIN(5, computedValue));

I would like to be able to write this as a single one-line macro. It must be free of side effects, in the same way that the existing system macros MIN and MAX are, and should work for the same data types as MIN and MAX.

Can anyone show me how to turn this into a single macro?

Can't you simply do that, define a min-max macro, _using_ the min and max macros? Or am I misunderstanding your question? — Some programmer dude, Feb 08 '13 at 09:41
Just for curiosity, is there any reason not to use std::min and std::max from the C++ standard library ? — kebs, Feb 08 '13 at 09:43
@kebs I'm mostly in objective-c. It does not fall naturally to use c++ functions :) — hfossli, Feb 08 '13 at 09:46
@ybungalobill Or bound, or clipped, or ... I think the most usual denomination depends on the application domain. — James Kanze, Feb 08 '13 at 09:49
Well, then, maybe remove the C++ tag, as C++ programmers tend to avoid macros, especially if the standard library provides a much better solution. — kebs, Feb 08 '13 at 10:38

hfossli · Accepted Answer · 2014-11-24T13:21:27.560

This is without side effects and works for any primitive number:

#define MIN(A,B)    ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a < __b ? __a : __b; })
#define MAX(A,B)    ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a < __b ? __b : __a; })

#define CLAMP(x, low, high) ({\
  __typeof__(x) __x = (x); \
  __typeof__(low) __low = (low);\
  __typeof__(high) __high = (high);\
  __x > __high ? __high : (__x < __low ? __low : __x);\
  })

Can be used like so

int clampedInt = CLAMP(computedValue, 3, 7);
double clampedDouble = CLAMP(computedValue, 0.5, 1.0);

Other suggested names instead of CLAMP can be VALUE_CONSTRAINED_LOW_HIGH, BOUNDS, CLIPPED.

score 3 · Answer 2 · answered Feb 08 '13 at 09:58

3

Taken from this site http://developer.gnome.org/glib/2.34/glib-Standard-Macros.html#CLAMP:CAPS

#define CLAMP(x, low, high)  (((x) > (high)) ? (high) : (((x) < (low)) ? (low) : (x)))

answered Feb 08 '13 at 09:58

hfossli

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Oh, side effects. `CLAMP(getchar(), low++, high--)` – aragaer Feb 08 '13 at 10:02
That's right. Good point!!! So that's why we should do like this http://stackoverflow.com/questions/3437404/min-and-max-in-c/3437484#3437484 and not use the default MIN and MAX like @VosobeKapsimanis suggests. – hfossli Feb 08 '13 at 10:05

score 2 · Answer 3 · answered Feb 08 '13 at 09:46

2

Maybe you want to try it like that:

template <class T> 
const T& clamp(const T& value, const T& low, const T& high) {
    return value < low ? low:
           value > high? high:
                         value;
}

answered Feb 08 '13 at 09:46

Udo Klein

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Or `return std::max( low, std::min( high, value ) );` – James Kanze Feb 08 '13 at 09:50

score 1 · Answer 4 · answered Feb 08 '13 at 09:56

1

 #define MAX(a, b) (((a) > (b)) ? (a) : (b)) 
 #define MIN(a, b) (((a) > (b)) ? (b) : (a))

making it in one #define directive isn't going to be very readable.

answered Feb 08 '13 at 09:56

Angelos Kapsimanis

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score -1 · Answer 5 · answered Feb 08 '13 at 09:55

-1

Using just one compare operation:

static inline int clamp(int value, int min, int max) {
    return min + MIN((unsigned int)(value - min), max - min)
}

answered Feb 08 '13 at 09:55

aragaer

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Well. Say the type of the value can change - I would prefer a macro? Do you agree? – hfossli Feb 08 '13 at 09:56
Yeah, would require some way to make "unsigned typeof" to turn it into macro. – aragaer Feb 08 '13 at 09:59
On the other hand assuming we're working with integral types only, `#define CLAMP(x, low, high) ({ typeof(low) _low = (low); LARGE_ENOUGH_UNSIGNED_TYPE _x = (x) - _low, _high = (high) - _low; (typeof(x)) MIN(_x, _high); })` – aragaer Feb 08 '13 at 10:08

How can I write a 'clamp' / 'clip' / 'bound' macro for returning a value in a given range?

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