[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=5866

RazvanN  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||razvan.nitu1...@gmail.com
 Resolution|--- |WORKSFORME

--- Comment #6 from RazvanN  ---
The code in the original bug report now compiles successfully on git HEAD
ubuntu 16.04. Closing as WORKSFORME.

--

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866



--- Comment #5 from bearophile_h...@eml.cc 2012-04-24 19:03:51 PDT ---
Now converted to enhancement by SomeDude.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866


SomeDude lovelyd...@mailmetrash.com changed:

   What|Removed |Added

 CC||lovelyd...@mailmetrash.com
   Severity|normal  |enhancement


-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866


Don clugd...@yahoo.com.au changed:

   What|Removed |Added

 CC||clugd...@yahoo.com.au


--- Comment #1 from Don clugd...@yahoo.com.au 2011-04-20 05:03:20 PDT ---
Bearophile, I don't think that would achieve what you think.

float  = float * float + float

contains a conversion from double to float.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866



--- Comment #2 from bearophile_h...@eml.cc 2011-04-20 09:44:40 PDT ---
(In reply to comment #1)
 float  = float * float + float
 
 contains a conversion from double to float.

Thank you for your comment. In programming I'm always finding new and new ways
to be wrong or just to show ignorance :-) But this program, gives no errors
with DMD 2.052:


float f1() { return 1.0f; }
float f2() { return 2.0f; }
float f3() { return 3.0f; }
void main() {
static assert(is(typeof(f1() * f2()) == float));
static assert(is(typeof(f1() * f2() + f3()) == float));
float result;
static assert(is(typeof(result = f1() * f2() + f3()) == float));
}


And a good C lint gives no double-error warnings in this C program:

float f1() { return 1.0f; }
float f2() { return 2.0f; }
float f3() { return 3.0f; }
int main() {
float result = f1() * f2() + f3();
return 0;
}


So where's the double-float conversion?

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866



--- Comment #3 from Don clugd...@yahoo.com.au 2011-04-20 12:34:16 PDT ---
(In reply to comment #2)
 (In reply to comment #1)
  float  = float * float + float
  
  contains a conversion from double to float.
 
 Thank you for your comment. In programming I'm always finding new and new ways
 to be wrong or just to show ignorance :-) But this program, gives no errors
 with DMD 2.052:
 
 
 float f1() { return 1.0f; }
 float f2() { return 2.0f; }
 float f3() { return 3.0f; }
 void main() {
 static assert(is(typeof(f1() * f2()) == float));
 static assert(is(typeof(f1() * f2() + f3()) == float));
 float result;
 static assert(is(typeof(result = f1() * f2() + f3()) == float));
 }
 
 
 And a good C lint gives no double-error warnings in this C program:
 
 float f1() { return 1.0f; }
 float f2() { return 2.0f; }
 float f3() { return 3.0f; }
 int main() {
 float result = f1() * f2() + f3();
 return 0;
 }
 
 
 So where's the double-float conversion?

It's not exactly a double-float conversion. But it's part of the same issue:
to what extent is the compiler allowed to perform floating-point promotions,
and use extra precision?

It shows up when f3 is negative, and slightly less than f1*f2. If the compiler
is using doubles for intermediate results (which it is allowed to do), the
results are not the same as if floats were used throughout. 
An obvious case is when f1 = float.max, f2 = 1.5, f3 = -float.max.
If it stays as float, the result will be +infinity. If intermediate doubles are
used, the result is 0.5 * float.max. (It affects precision as well as range,
but the range examples are more obvious).
Floating point multiply-accumulate (FMA) can do the same thing.

As long as you support x87, or allow FMA, this stuff is inevitable.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---

[Issue 5866] std.math.sin(float), std.math.cos(float) to return float

[d-bugmail]

http://d.puremagic.com/issues/show_bug.cgi?id=5866



--- Comment #4 from bearophile_h...@eml.cc 2011-04-20 14:39:26 PDT ---
(In reply to comment #3)

 As long as you support x87, or allow FMA, this stuff is inevitable.

Lot of complexities, I see.

Going back to the point of this enhancement request, if cos(float) and
sin(float) return a double, there is zero chance that the intermediate
computations get performed among floats. So I think this enhancement request
stands still.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
--- You are receiving this mail because: ---