Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 05:47:43 UTC, Paul Jurczak wrote:
I'm writing this rather ugly:
sqrt(cast(float)D) != round(sqrt(cast(float)D)
line and I'm looking for more concise notation without
introducing a meaningless variable to hold expression being
tested. Is there an equivalent of std.math.trunc(), which would
return fractional portion instead, maybe frac()?
I defined a helper function:
bool isIntegral(T)(T x) {return x == round(x);}
but is there something in D libraries to give me this
functionality?
Re: What is a concise way to test if floating point value is integral?
On Thursday, August 29, 2013 07:47:16 Paul Jurczak wrote: I'm writing this rather ugly: sqrt(cast(float)D) != round(sqrt(cast(float)D) line and I'm looking for more concise notation without introducing a meaningless variable to hold expression being tested. Is there an equivalent of std.math.trunc(), which would return fractional portion instead, maybe frac()? There may be something in std.math which makes it cleaner, but I would have thought that the to test whether a floating point value is an integral value, you'd just cast it to an integral type and then compare that against the original. e.g. auto isIntegral = cast(int)my_float == my_float; - Jonathan M Davis
Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 06:23:18 UTC, Jonathan M Davis wrote: On Thursday, August 29, 2013 07:47:16 Paul Jurczak wrote: I'm writing this rather ugly: sqrt(cast(float)D) != round(sqrt(cast(float)D) line and I'm looking for more concise notation without introducing a meaningless variable to hold expression being tested. Is there an equivalent of std.math.trunc(), which would return fractional portion instead, maybe frac()? There may be something in std.math which makes it cleaner, but I would have thought that the to test whether a floating point value is an integral value, you'd just cast it to an integral type and then compare that against the original. e.g. auto isIntegral = cast(int)my_float == my_float; - Jonathan M Davis Isn't type conversion: auto isIntegral = to!int(my_float) == my_float; more recommended/idiomatic D way to deal with built-in types?
Re: What is a concise way to test if floating point value is integral?
On Thursday, August 29, 2013 08:50:47 Paul Jurczak wrote: On Thursday, 29 August 2013 at 06:23:18 UTC, Jonathan M Davis wrote: On Thursday, August 29, 2013 07:47:16 Paul Jurczak wrote: I'm writing this rather ugly: sqrt(cast(float)D) != round(sqrt(cast(float)D) line and I'm looking for more concise notation without introducing a meaningless variable to hold expression being tested. Is there an equivalent of std.math.trunc(), which would return fractional portion instead, maybe frac()? There may be something in std.math which makes it cleaner, but I would have thought that the to test whether a floating point value is an integral value, you'd just cast it to an integral type and then compare that against the original. e.g. auto isIntegral = cast(int)my_float == my_float; - Jonathan M Davis Isn't type conversion: auto isIntegral = to!int(my_float) == my_float; more recommended/idiomatic D way to deal with built-in types? Not really IMHO. std.conv.to does fancier conversions than casting does, and it throws in cases of overflow, neither of which are of any benefit when converting a float to an int, as any integral value in a float will fit in an int. Using to would just create extra overhead for no extra benefit in this case. - Jonathan M Davis
Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis wrote: [..] as any integral value in a float will fit in an int. [..] Will it? Most of them will not fit, but cast to int produces nonsensical value anyway as in this example: cast(int)float.max With to!int you get a proper warning.
Re: What is a concise way to test if floating point value is integral?
On Thursday, August 29, 2013 10:07:31 Paul Jurczak wrote: On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis wrote: [..] as any integral value in a float will fit in an int. [..] Will it? Most of them will not fit Sure, they will. float has 32 bits, just like int, so it can't possibly hold a value larger than an int can hold. This code passes with flying colors foreach(i; int.min .. int.max) assert(cast(float)i == i); but cast to int produces nonsensical value anyway as in this example: cast(int)float.max So what? All you care about here is whether the value in the float is an integral value. float.max isn't an integral value, so it really doesn't matter if you get overflow when converting. It would have to convert back to the exact same value when converting it back to a float, and it won't. assert(cast(int)float.max == float.max); will fail. It might make more sense to use to!int if you want to use the resulting int for something, but all you're doing with it is comparing it against the original float to see if it's the same value. If anything, the fact that to!int throws would be a serious problem for what you're trying to do, because if what you're testing for is whether a float holds an integral value, throwing on overflow when converting to int would just get in your way. It should just result in false in that case (because it's not an integral value, or it wouldn't overflow), and the cast will result in false, unlike to!int. - Jonathan M Davis
Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 08:26:11 UTC, Jonathan M Davis
wrote:
On Thursday, August 29, 2013 10:07:31 Paul Jurczak wrote:
On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis
wrote:
[..]
as any integral value in a float will fit in an
int.
[..]
Will it? Most of them will not fit
Sure, they will. float has 32 bits, just like int, so it can't
possibly hold a
value larger than an int can hold. This code passes with flying
colors
foreach(i; int.min .. int.max)
assert(cast(float)i == i);
but cast to int produces
nonsensical value anyway as in this example:
cast(int)float.max
So what? All you care about here is whether the value in the
float is an
integral value. float.max isn't an integral value, so it really
doesn't matter
if you get overflow when converting. It would have to convert
back to the exact
same value when converting it back to a float, and it won't.
assert(cast(int)float.max == float.max);
will fail. It might make more sense to use to!int if you want
to use the
resulting int for something, but all you're doing with it is
comparing it
against the original float to see if it's the same value. If
anything, the fact
that to!int throws would be a serious problem for what you're
trying to do,
because if what you're testing for is whether a float holds an
integral value,
throwing on overflow when converting to int would just get in
your way. It
should just result in false in that case (because it's not an
integral value,
or it wouldn't overflow), and the cast will result in false,
unlike to!int.
- Jonathan M Davis
I should have used integer instead of integral to avoid math
vs. programming language confusion.
Well, float.max is an integer number! Its value is 3.40282e+38.
The function I defined at the top of this page:
bool isIntegral(T)(T x) {return x == round(x);}
works correctly with float.max. Using cast(int) fails. I should
have written it as:
bool isInteger(T)(T x) {return x == round(x);}
Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 08:26:11 UTC, Jonathan M Davis wrote: On Thursday, August 29, 2013 10:07:31 Paul Jurczak wrote: On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis wrote: [..] as any integral value in a float will fit in an int. [..] Will it? Most of them will not fit Sure, they will. float has 32 bits, just like int, so it can't possibly hold a value larger than an int can hold. float can't hold more distinct values than int, but a float can have integer values greater than int.max. (Also, there are int values that a float cannot store.) This code passes with flying colors foreach(i; int.min .. int.max) assert(cast(float)i == i); That's because both sides are casted to float. [...] float.max isn't an integral value, It's not a value that an int can store, but it's an integer in the mathematical sense.
Re: What is a concise way to test if floating point value is integral?
On Thursday, 29 August 2013 at 08:58:02 UTC, Paul Jurczak wrote:
On Thursday, 29 August 2013 at 08:26:11 UTC, Jonathan M Davis
wrote:
On Thursday, August 29, 2013 10:07:31 Paul Jurczak wrote:
On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis
wrote:
[..]
as any integral value in a float will fit in an
int.
[..]
Will it? Most of them will not fit
Sure, they will. float has 32 bits, just like int, so it can't
possibly hold a
value larger than an int can hold. This code passes with
flying colors
foreach(i; int.min .. int.max)
assert(cast(float)i == i);
but cast to int produces
nonsensical value anyway as in this example:
cast(int)float.max
So what? All you care about here is whether the value in the
float is an
integral value. float.max isn't an integral value, so it
really doesn't matter
if you get overflow when converting. It would have to convert
back to the exact
same value when converting it back to a float, and it won't.
assert(cast(int)float.max == float.max);
will fail. It might make more sense to use to!int if you want
to use the
resulting int for something, but all you're doing with it is
comparing it
against the original float to see if it's the same value. If
anything, the fact
that to!int throws would be a serious problem for what you're
trying to do,
because if what you're testing for is whether a float holds an
integral value,
throwing on overflow when converting to int would just get in
your way. It
should just result in false in that case (because it's not an
integral value,
or it wouldn't overflow), and the cast will result in false,
unlike to!int.
- Jonathan M Davis
I should have used integer instead of integral to avoid
math vs. programming language confusion.
Well, float.max is an integer number! Its value is 3.40282e+38.
The function I defined at the top of this page:
bool isIntegral(T)(T x) {return x == round(x);}
works correctly with float.max. Using cast(int) fails. I should
have written it as:
bool isInteger(T)(T x) {return x == round(x);}
Yes, casting will not work because a float type can't be fully
cast to an int without possible overflow.
Your method works fine. The only issue, the issue with comparing
any floating point, is tolerance. How close to an int does a
float have to be to be considered an int?
If you can afford to do something like `return (abs(x - round(x))
tol)`.
(remember, numerical computations can result in floating point
numbers that are suppose be integers but are not(accumulation of
rounding errors). Using == results in using the tolerance of a
float, its minimum value)
Also look at FXTRACT.
Re: What is a concise way to test if floating point value is integral?
On 2013-08-29, 10:25, Jonathan M Davis wrote:
On Thursday, August 29, 2013 10:07:31 Paul Jurczak wrote:
On Thursday, 29 August 2013 at 07:51:40 UTC, Jonathan M Davis
wrote:
[..]
as any integral value in a float will fit in an
int.
[..]
Will it? Most of them will not fit
Sure, they will. float has 32 bits, just like int, so it can't possibly
hold a
value larger than an int can hold. This code passes with flying colors
foreach(i; int.min .. int.max)
assert(cast(float)i == i);
First, that's showing the exact opposite of what you're saying it does.
Second, it doesn't even show that.
Your code is equivalent to:
foreach(i; int.min .. int.max)
assert(cast(float)i == cast(float)i);
If that does not pass with flying colors, I'd be surprised. Now try this:
foreach(i; int.min .. int.max) {
float f = i; // DMD optimizes out cast(int)cast(float)int
assert(cast(int)f == i);
}
It will fail for odd numbers in the range 16,777,216-33,554,432, and for
numbers not divisible by 4 in the range to the next power of two, then 8,
and so on. These numbers are simply not representable by a float.
For more information:
http://floating-point-gui.de/formats/fp/
--
Simen
What is a concise way to test if floating point value is integral?
I'm writing this rather ugly: sqrt(cast(float)D) != round(sqrt(cast(float)D) line and I'm looking for more concise notation without introducing a meaningless variable to hold expression being tested. Is there an equivalent of std.math.trunc(), which would return fractional portion instead, maybe frac()?
