digitalmars.D.learn - formatting floating point
- "Saaa" <empty needmail.com> Jul 11 2009
- Jarrett Billingsley <jarrett.billingsley gmail.com> Jul 11 2009
- "Saaa" <empty needmail.com> Jul 11 2009
- Jarrett Billingsley <jarrett.billingsley gmail.com> Jul 11 2009
- "Saaa" <empty needmail.com> Jul 11 2009
- Jarrett Billingsley <jarrett.billingsley gmail.com> Jul 11 2009
- "Saaa" <empty needmail.com> Jul 11 2009
- Don <nospam nospam.com> Jul 13 2009
- "Saaa" <empty needmail.com> Jul 13 2009
double d[2] = [ 0, 1, double.max]; char[] c = format(d); How do I get c to represent full precision? "[0,1,1.7976931348623157e+308]" // but then with double.max being represented fully
Jul 11 2009
On Sat, Jul 11, 2009 at 5:50 PM, Saaa<empty needmail.com> wrote:double d[2] =3D [ 0, 1, double.max]; char[] c =3D format(d); =A0How do I get c to represent full precision? "[0,1,1.7976931348623157e+308]" // but then with double.max being represented fully
You want a 309-digit number consisting mostly of 0s?
Jul 11 2009
"Saaa" <empty needmail.com> double d[2] = [ 0, 1, double.max]; char[] c = format(d); How do I get c to represent full precision? "[0,1,1.7976931348623157e+308]" // but then with double.max being represented fully
You want a 309-digit number consisting mostly of 0s?
Yes, but only if they are necessary. 0 doesn't need all hose digits for instance. What else is the point in saving doubles.
Jul 11 2009
On Sat, Jul 11, 2009 at 6:44 PM, Saaa<empty needmail.com> wrote:double d[2] = [ 0, 1, double.max]; char[] c = format(d); How do I get c to represent full precision? "[0,1,1.7976931348623157e+308]" // but then with double.max being represented fully
You want a 309-digit number consisting mostly of 0s?
Yes, but only if they are necessary. 0 doesn't need all hose digits for instance.
Um, doubles don't have infinite precision. See those digits that it output? That's all you get. Those are the only digits that are necessary because those are the only digits that are *stored*. Just because it's followed by almost 300 0s doesn't mean that 300 0s are actually stored in the number; it just means the exponent is that large.What else is the point in saving doubles.
If you're saving doubles in a textual format, try using the %a format specifier. It outputs a float in hexadecimal notation, which is a bit more precise than decimal (since no rounding has to be performed). I don't know if Phobos' unformatting can actually _read_ hex floats, though.
Jul 11 2009
"Jarrett Billingsley" <jarrett.billingsley gmail.com> wrote in message news:mailman.51.1247352795.14071.digitalmars-d-learn puremagic.com...On Sat, Jul 11, 2009 at 6:44 PM, Saaa<empty needmail.com> wrote:double d[2] = [ 0, 1, double.max]; char[] c = format(d); How do I get c to represent full precision? "[0,1,1.7976931348623157e+308]" // but then with double.max being represented fully
You want a 309-digit number consisting mostly of 0s?
Yes, but only if they are necessary. 0 doesn't need all hose digits for instance.
Um, doubles don't have infinite precision. See those digits that it output? That's all you get. Those are the only digits that are necessary because those are the only digits that are *stored*. Just because it's followed by almost 300 0s doesn't mean that 300 0s are actually stored in the number; it just means the exponent is that large.
I now see what you mean by 309 digits.. No I don't want that !! :D string.format does only 6 digits by default, I added the extra double.max digits in myself from wikipedia :) I overestimated the precision of a double, my bad. (53bits != 309 digits !) How can I format to the full number of digits, like I did for c?What else is the point in saving doubles.
If you're saving doubles in a textual format, try using the %a format specifier. It outputs a float in hexadecimal notation, which is a bit more precise than decimal (since no rounding has to be performed). I don't know if Phobos' unformatting can actually _read_ hex floats, though.
I could add the option, but for now I'm going for human readability
Jul 11 2009
On Sat, Jul 11, 2009 at 7:39 PM, Saaa<empty needmail.com> wrote:Um, doubles don't have infinite precision. =A0See those digits that it output? =A0That's all you get. =A0Those are the only digits that are necessary because those are the only digits that are *stored*. =A0Just because it's followed by almost 300 0s doesn't mean that 300 0s are actually stored in the number; it just means the exponent is that large.
I now see what you mean by 309 digits.. No I don't want that !! :D string.format does only 6 digits by default, I added the extra double.max digits in myself from wikipedia :) I overestimated the precision of a double, my bad. (53bits !=3D 309 digits !) How can I format to the full number of digits, like I did for c?
Ohh, I see. Your initial question was really vague, now that I see what you were asking. You'd just have to convert each element of the array separately.
Jul 11 2009
Ohh, I see. Your initial question was really vague, now that I see what you were asking.
You'd just have to convert each element of the array separately.
I found the formatting options, they are in std.format.. (I was apparently searching for the 'g' option.. ) this seems to work (using std2.string.format) double[] d1; d1=[double.max,double.min]; char[] c; c=format( "%.100g",d1); //100 is enough for reals I think? writefln(c); //[1.7976931348623157079e+308,2.2250738585072013832e-308]
Jul 11 2009
Saaa wrote:Ohh, I see. Your initial question was really vague, now that I see what you were asking.
You'd just have to convert each element of the array separately.
I found the formatting options, they are in std.format.. (I was apparently searching for the 'g' option.. ) this seems to work (using std2.string.format) double[] d1; d1=[double.max,double.min]; char[] c; c=format( "%.100g",d1); //100 is enough for reals I think? writefln(c); //[1.7976931348623157079e+308,2.2250738585072013832e-308]
Jul 13 2009
You'd just have to convert each element of the array separately.
I found the formatting options, they are in std.format.. (I was apparently searching for the 'g' option.. ) this seems to work (using std2.string.format) double[] d1; d1=[double.max,double.min]; char[] c; c=format( "%.100g",d1); //100 is enough for reals I think? writefln(c); //[1.7976931348623157079e+308,2.2250738585072013832e-308]
But choosing an insane big number of precision in combination with g seems to work perfectly already. Although there probably is a better formatting option, I hope.
Jul 13 2009