Re: signbit question
On Friday, 16 March 2018 at 08:35:58 UTC, Radu wrote:
On Friday, 16 March 2018 at 07:00:36 UTC, ashit axar wrote:
On Thursday, 15 March 2018 at 17:30:48 UTC, Seb wrote:
They generate the same assembly: https://godbolt.org/g/4ohTJx
import std.stdio;
void main()
{
writeln("hello");
}
this generate error for dmd there.
`writeln` is not supported in betterC for dmd. Use `printf`
instead.
Or remove -betterC. I just used it because then no module
constructors/destructors are generated and thus the assembly is
even shorter.
Re: signbit question
On Friday, 16 March 2018 at 07:00:36 UTC, ashit axar wrote:
On Thursday, 15 March 2018 at 17:30:48 UTC, Seb wrote:
They generate the same assembly: https://godbolt.org/g/4ohTJx
import std.stdio;
void main()
{
writeln("hello");
}
this generate error for dmd there.
`writeln` is not supported in betterC for dmd. Use `printf`
instead.
Re: signbit question
On Thursday, 15 March 2018 at 17:30:48 UTC, Seb wrote:
They generate the same assembly: https://godbolt.org/g/4ohTJx
import std.stdio;
void main()
{
writeln("hello");
}
this generate error for dmd there.
Re: signbit question
Miguel L wrote: as the calculations on f guarantee it cannot be 0 at all. than `f` will become zero very soon. something that "cannot happen" is the most probable thing to happen. otherwise, LGTM.
Re: signbit question
On 3/15/2018 12:39 PM, Miguel L wrote:
On Thursday, 15 March 2018 at 17:31:38 UTC, rumbu wrote:
On Thursday, 15 March 2018 at 17:18:08 UTC, Miguel L wrote:
On Thursday, 15 March 2018 at 16:31:56 UTC, Stefan Koch wrote:
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote:
[...]
integers don't have a sign-bit.
since they are not necessarily singed.
However if an integer is signed and using 1-complement
you can either do sign = var < 0 or
sign = (var & (1 << (sizeof(var)*8 - 1));
though I cannot tell which one is faster you have to experiment.
Thanks. Just one more question:
Is this code correct? I don't care about +0 or -0 as the calculations
on f guarantee it cannot be 0 at all.
int a;
float f;
if((a<0)==signbit(f)) {}
else {...}
If you are comparing with an integer, please avoid signbit. It will
return 1 also for -0.0, -inf and -nan.
Don't bother also with signbit for integer types. The compiler usually
outsmarts the programmer in finding the best way to compare an integer
with 0.
You can simply write:
if (a < 0 && f < 0) {...}
This will cover the [-inf..0) but not the NaN case. You can test it in
a separate branch
if (isNaN(f)) {...}
There are various in my code there are more than two variables, and i'd
like to check when their signs differ.I am trying to avoid this, maybe
there is no point in it:
if(!((a>=0 && f>=0) || (a<0 && f<0))){
//signs are different
}
Thanks, anyway
You could simplify that to this:
if ((a < 0) != (f < 0))
{
}
Or if you have more than two variables you could do something like this:
bool AllSameSign(double[] args ...)
{
//Only need to check if there are more than one of them
if (args.length > 1)
{
//Compare arg[0] to all the other args.
for (int i = 1; i < args.length; i++)
{
if ((args[0] < 0) != (args[i] < 0))
{
return false;
}
}
}
return true;
}
Which you could call like this, with as many variables as you like:
AllSameSign(a,f);
Re: signbit question
On Thursday, 15 March 2018 at 17:31:38 UTC, rumbu wrote:
On Thursday, 15 March 2018 at 17:18:08 UTC, Miguel L wrote:
On Thursday, 15 March 2018 at 16:31:56 UTC, Stefan Koch wrote:
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote:
[...]
integers don't have a sign-bit.
since they are not necessarily singed.
However if an integer is signed and using 1-complement
you can either do sign = var < 0 or
sign = (var & (1 << (sizeof(var)*8 - 1));
though I cannot tell which one is faster you have to
experiment.
Thanks. Just one more question:
Is this code correct? I don't care about +0 or -0 as the
calculations on f guarantee it cannot be 0 at all.
int a;
float f;
if((a<0)==signbit(f)) {}
else {...}
If you are comparing with an integer, please avoid signbit. It
will return 1 also for -0.0, -inf and -nan.
Don't bother also with signbit for integer types. The compiler
usually outsmarts the programmer in finding the best way to
compare an integer with 0.
You can simply write:
if (a < 0 && f < 0) {...}
This will cover the [-inf..0) but not the NaN case. You can
test it in a separate branch
if (isNaN(f)) {...}
There are various in my code there are more than two variables,
and i'd like to check when their signs differ.I am trying to
avoid this, maybe there is no point in it:
if(!((a>=0 && f>=0) || (a<0 && f<0))){
//signs are different
}
Thanks, anyway
Re: signbit question
On Thursday, 15 March 2018 at 17:18:08 UTC, Miguel L wrote:
On Thursday, 15 March 2018 at 16:31:56 UTC, Stefan Koch wrote:
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote:
Why does std.math.signbit only work for floating point types?
Is there an analogue function for integer types? what is the
best way to compare the sign of a float with the sign of an
integer?
Thanks in advance
integers don't have a sign-bit.
since they are not necessarily singed.
However if an integer is signed and using 1-complement
you can either do sign = var < 0 or
sign = (var & (1 << (sizeof(var)*8 - 1));
though I cannot tell which one is faster you have to
experiment.
Thanks. Just one more question:
Is this code correct? I don't care about +0 or -0 as the
calculations on f guarantee it cannot be 0 at all.
int a;
float f;
if((a<0)==signbit(f)) {}
else {...}
If you are comparing with an integer, please avoid signbit. It
will return 1 also for -0.0, -inf and -nan.
Don't bother also with signbit for integer types. The compiler
usually outsmarts the programmer in finding the best way to
compare an integer with 0.
You can simply write:
if (a < 0 && f < 0) {...}
This will cover the [-inf..0) but not the NaN case. You can test
it in a separate branch
if (isNaN(f)) {...}
Re: signbit question
On Thursday, 15 March 2018 at 16:31:56 UTC, Stefan Koch wrote: On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote: Why does std.math.signbit only work for floating point types? Is there an analogue function for integer types? what is the best way to compare the sign of a float with the sign of an integer? Thanks in advance integers don't have a sign-bit. since they are not necessarily singed. However if an integer is signed and using 1-complement you can either do sign = var < 0 or sign = (var & (1 << (sizeof(var)*8 - 1)); though I cannot tell which one is faster you have to experiment. They generate the same assembly: https://godbolt.org/g/4ohTJx
Re: signbit question
On Thursday, 15 March 2018 at 16:31:56 UTC, Stefan Koch wrote:
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote:
Why does std.math.signbit only work for floating point types?
Is there an analogue function for integer types? what is the
best way to compare the sign of a float with the sign of an
integer?
Thanks in advance
integers don't have a sign-bit.
since they are not necessarily singed.
However if an integer is signed and using 1-complement
you can either do sign = var < 0 or
sign = (var & (1 << (sizeof(var)*8 - 1));
though I cannot tell which one is faster you have to experiment.
Thanks. Just one more question:
Is this code correct? I don't care about +0 or -0 as the
calculations on f guarantee it cannot be 0 at all.
int a;
float f;
if((a<0)==signbit(f)) {}
else {...}
Re: signbit question
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote: Why does std.math.signbit only work for floating point types? Is there an analogue function for integer types? what is the best way to compare the sign of a float with the sign of an integer? Thanks in advance integers don't have a sign-bit. since they are not necessarily singed. However if an integer is signed and using 1-complement you can either do sign = var < 0 or sign = (var & (1 << (sizeof(var)*8 - 1)); though I cannot tell which one is faster you have to experiment.
Re: signbit question
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote: Why does std.math.signbit only work for floating point types? Integers are stored in an entirely different way, twos-complement instead of having a sign bit. You probably shouldn't be using the sign bit function at all, it is for digging deeper into the float binary format. Instead, I'd just say if(f > 0 && i > 0) if(f < 0 && i < 0) if(f == 0 && i == 0) etc. in math stuff to see if they have the same sign. floats have weird things like +0 and -0 which doesn't exist at all in ints...
Re: signbit question
On Thursday, 15 March 2018 at 15:28:16 UTC, Miguel L wrote:
Why does std.math.signbit only work for floating point types?
Is there an analogue function for integer types?
I guess because for integers you don't need to distinguish
between +0.0 and -0.0, so no one bother until now to add it to
std.math.
That being said there are a few options for integer types:
---
import std.math, std.stdio;
void main()
{
foreach (a; -1 .. 2)
{
"a:".writeln(a);
signbit(cast(double) a).writefln!"signbit: %2d";
(cast(uint) a >> a.sizeof * 8 - 1).writefln!"bitshift: %2d";
(a < 0).writefln!"< 0:\t %2d";
writeln;
}
}
---
https://run.dlang.io/is/pts6dj
The first option is a bit slower for integers and the second and
third option generate equivalent assembly [1], so I would
recommend `a < 0` for integer types.
[1] https://godbolt.org/g/4ohTJx
what is the best way to compare the sign of a float with the
sign of an integer?
Ideas:
1) Make a PR to signbit to add integer support
2) Create your own signsbit a la:
---
auto signbit(A)(A a)
{
static import std.math;
import std.traits : isIntegral;
static if (isIntegral!A)
return a < 0;
else
return std.math.signbit(a);
}
---
signbit question
Why does std.math.signbit only work for floating point types? Is there an analogue function for integer types? what is the best way to compare the sign of a float with the sign of an integer? Thanks in advance
