## digitalmars.D - double.min - should be 5e-324?

- Dmitry Olshansky (18/18) Dec 04 2010 Well, to keep things short, double.min returns something weird.
- so (5/8) Dec 04 2010 That is something weird, you get a double smaller than the smallest
- so (4/4) Dec 04 2010 See what you mean, but it is the standard value from c's float.h.
- Dmitry Olshansky (5/11) Dec 04 2010 To prove the above point.
- Dmitry Olshansky (5/21) Dec 04 2010 the last line should be:
- Ellery Newcomer (3/19) Dec 04 2010 looks like double.min is returning double.min_normal
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= (5/7) Dec 04 2010 Yeah, things got changed a while back for floating point types. .min now...
- sybrandy (4/20) Dec 04 2010 Perhaps this link can help:
- Don (3/23) Dec 04 2010 double.min is deprecated, for exactly this reason. That's why it's not
- Don (4/27) Dec 04 2010 And futher -- double.min_normal is the smallest normalised double. The
- Dmitry Olshansky (4/31) Dec 05 2010 I see, thanks for the explanation.

Well, to keep things short, double.min returns something weird. See the following for demonstration: import std.stdio; void main(){ double r = double.max, r2 = double.min; writeln(r);//1.79769e+308 r *= 2;//test if it's max writeln(r); // infinity, ok writeln(r2);//2.22507e-308, wtf ? r2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of above double dmin = 5e-324; writeln(dmin);// 4.94066e-324 dmin /= 2.0; writefln(dmin);// 0 } -- Dmitry Olshansky

Dec 04 2010

writeln(r2);//2.22507e-308, wtf ?What is wrong? It is the smallest representable double. not (-double.max)r2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of aboveThat is something weird, you get a double smaller than the smallest representable! -- Using Opera's revolutionary email client: http://www.opera.com/mail/

Dec 04 2010

See what you mean, but it is the standard value from c's float.h. This is not my day, i should just stop posting... -- Using Opera's revolutionary email client: http://www.opera.com/mail/

Dec 04 2010

On 05.12.2010 0:48, so wrote:The smallest is 5e-324 as I (hopefully) showed.writeln(r2);//2.22507e-308, wtf ?What is wrong? It is the smallest representable double. not (-double.max)To prove the above point. -- Dmitry Olshanskyr2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of aboveThat is something weird, you get a double smaller than the smallest representable!

Dec 04 2010

On 05.12.2010 0:22, Dmitry Olshansky wrote:Well, to keep things short, double.min returns something weird. See the following for demonstration: import std.stdio; void main(){ double r = double.max, r2 = double.min; writeln(r);//1.79769e+308 r *= 2;//test if it's max writeln(r); // infinity, ok writeln(r2);//2.22507e-308, wtf ? r2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of above double dmin = 5e-324; writeln(dmin);// 4.94066e-324 dmin /= 2.0; writefln(dmin);// 0 }the last line should be: writeln(dmin); //0 -- Dmitry Olshansky

Dec 04 2010

On 12/04/2010 03:22 PM, Dmitry Olshansky wrote:Well, to keep things short, double.min returns something weird. See the following for demonstration: import std.stdio; void main(){ double r = double.max, r2 = double.min; writeln(r);//1.79769e+308 r *= 2;//test if it's max writeln(r); // infinity, ok writeln(r2);//2.22507e-308, wtf ? r2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of above double dmin = 5e-324; writeln(dmin);// 4.94066e-324 dmin /= 2.0; writefln(dmin);// 0 }looks like double.min is returning double.min_normal oddly enough, double.min is undefined in the spec

Dec 04 2010

Ellery Newcomer wrote:looks like double.min is returning double.min_normal oddly enough, double.min is undefined in the specYeah, things got changed a while back for floating point types. .min now returns the minimum normal. To get the actual minimum value, we need to use the negative of .max. Ali

Dec 04 2010

On 12/04/2010 04:22 PM, Dmitry Olshansky wrote:Well, to keep things short, double.min returns something weird. See the following for demonstration: import std.stdio; void main(){ double r = double.max, r2 = double.min; writeln(r);//1.79769e+308 r *= 2;//test if it's max writeln(r); // infinity, ok writeln(r2);//2.22507e-308, wtf ? r2 /= 2.0; writeln(r2);// 1.11254e-308, a logical consequence of above double dmin = 5e-324; writeln(dmin);// 4.94066e-324 dmin /= 2.0; writefln(dmin);// 0 }Perhaps this link can help: https://secure.wikimedia.org/wikipedia/en/wiki/IEEE_754-1985 Casey

Dec 04 2010

Dmitry Olshansky wrote:

Dec 04 2010

Don wrote:Dmitry Olshansky wrote:And futher -- double.min_normal is the smallest normalised double. The smallest representable double is (double.min_normal * double.epsilon). double.min is a silly name, so it has been deprecated.

Dec 04 2010

On 05.12.2010 8:59, Don wrote:Don wrote:I see, thanks for the explanation. -- Dmitry OlshanskyDmitry Olshansky wrote:And futher -- double.min_normal is the smallest normalised double. The smallest representable double is (double.min_normal * double.epsilon). double.min is a silly name, so it has been deprecated.

Dec 05 2010