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digitalmars.D.learn - Turn a float into a value between 0 and 1 (inclusive)?

reply Chirs Forest <CF chrisforest.com> writes:
I'm interpolating some values and I need to make an 
(elapsed_time/duration) value a float between 0 and 1 (inclusive 
of 0 and 1). The elapsed_time might be more than the duration, 
and in some cases might be 0 or less. What's the most efficient 
way to cap out of bounds values to 0 and 1? I can do a check and 
cap them manually, but if I'm doing a lot of these operations I'd 
like to pick the least resource intensive way.

Also, if I wanted out of bounds values to wrap (2.5 becomes 0.5) 
how would I get that value and also have 1.0 not give me 0.0?
Nov 21
next sibling parent reply Petar Kirov [ZombineDev] <petar.p.kirov gmail.com> writes:
On Tuesday, 21 November 2017 at 09:21:29 UTC, Chirs Forest wrote:
 I'm interpolating some values and I need to make an 
 (elapsed_time/duration) value a float between 0 and 1 
 (inclusive of 0 and 1). The elapsed_time might be more than the 
 duration, and in some cases might be 0 or less. What's the most 
 efficient way to cap out of bounds values to 0 and 1? I can do 
 a check and cap them manually, but if I'm doing a lot of these 
 operations I'd like to pick the least resource intensive way.

 Also, if I wanted out of bounds values to wrap (2.5 becomes 
 0.5) how would I get that value and also have 1.0 not give me 
 0.0?
Is this what you're looking for: https://www.desmos.com/calculator/8iytgsr3y3 In which case that would be simply: T zeroToOne(T)(T val) { return val % 1; }
Nov 21
parent Petar Kirov [ZombineDev] <petar.p.kirov gmail.com> writes:
On Tuesday, 21 November 2017 at 09:53:33 UTC, Petar Kirov 
[ZombineDev] wrote:
 On Tuesday, 21 November 2017 at 09:21:29 UTC, Chirs Forest 
 wrote:
 I'm interpolating some values and I need to make an 
 (elapsed_time/duration) value a float between 0 and 1 
 (inclusive of 0 and 1). The elapsed_time might be more than 
 the duration, and in some cases might be 0 or less. What's the 
 most efficient way to cap out of bounds values to 0 and 1? I 
 can do a check and cap them manually, but if I'm doing a lot 
 of these operations I'd like to pick the least resource 
 intensive way.

 Also, if I wanted out of bounds values to wrap (2.5 becomes 
 0.5) how would I get that value and also have 1.0 not give me 
 0.0?
Is this what you're looking for: https://www.desmos.com/calculator/8iytgsr3y3 In which case that would be simply: T zeroToOne(T)(T val) { return val % 1; }
The problem, as you can see in the plot is that 0.9(9) remains 0.9(9), however 1.0 and 1.0000001 become 0.0 and 0.0000001 respectively and there's no way around this due to the inherent discontinuity of the function.
Nov 21
prev sibling parent Biotronic <simen.kjaras gmail.com> writes:
On Tuesday, 21 November 2017 at 09:21:29 UTC, Chirs Forest wrote:
 I'm interpolating some values and I need to make an 
 (elapsed_time/duration) value a float between 0 and 1 
 (inclusive of 0 and 1). The elapsed_time might be more than the 
 duration, and in some cases might be 0 or less. What's the most 
 efficient way to cap out of bounds values to 0 and 1? I can do 
 a check and cap them manually, but if I'm doing a lot of these 
 operations I'd like to pick the least resource intensive way.
Good old comparisons should be plenty in this case: T clamp(T)(T value, T min, T max) { return value < min ? min : value > max ? max : value; } That's two comparisons and two conditional moves. You're not gonna beat that.
 Also, if I wanted out of bounds values to wrap (2.5 becomes 
 0.5) how would I get that value and also have 1.0 not give me 
 0.0?
As Petar points out, this is somewhat problematic. You think of the codomain (set of possible results) as being the size (1.0 - 0.0) = 1.0. However, since you include 1.0 in the set, the size is actually 1.0 + ε, which is very slightly larger. You could use a slightly modified version of Petar's function: T zeroToOne(T)(T val) { return val % (1+T.epsilon); } However, this induces rounding errors on larger numbers. e.g. 1.0 + ε becomes 0, while you'd want it to be ε. I guess I should ask for some clarification - what would you expect the return value to be for 2.0? Is that 0.0 or 1.0? How about for -1.0? A simple function that does give the results you want between 0.0 and 1.0 (inclusive) is this: T zeroToOne(T)(T val) { if (val >= 0 && val <= 1.0) { return val; } return val % 1; } The problem now, however, is that zeroToOne gives negative results for negative values. This is probably not what you want. This can be fixed with std.math.signbit: T zeroToOne(T)(T val) { import std.math : signbit; if (val >= 0 && val <= 1.0) { return val; } return (val % 1) + val.signbit; } If you're willing to give up the last 1/8388608th of precision (for float, 1/4503599627370496th for double) that including 1.0 gives you, this can become: T zeroToOne(T)(T val) { import std.math : signbit; return (val % 1) + val.signbit; } Which is easier to read, and consistent for values outside the [0,1) interval. -- Biotronic
Nov 21