Hi,
Does the Double has the facilty to define -0.
If it has, "==" or System.Math.Sign() doesn't able to differentiate between -0 & 0.
i.e.
Double x = -0.0d
Double y = 0.0d
if(value == -0.0d) {//both x & y drops in this statement.
//is minus zero
}
else {
//Not minus zero
}
How to differentiate -0.0d & 0.0d in if statement?
Thank you,
Avin Patel 8 4616
Avin Patel wrote: How to differentiate -0.0d & 0.0d in if statement?
How can a sign have any meaning when discussing the absence of a value?
--
Things never go according to plan. So plan accordingly.
Avin Patel wrote: Hi, Does the Double has the facilty to define -0.
If it has, "==" or System.Math.Sign() doesn't able to differentiate between -0 & 0.
i.e. Double x = -0.0d Double y = 0.0d
if(value == -0.0d) {//both x & y drops in this statement. //is minus zero } else { //Not minus zero }
How to differentiate -0.0d & 0.0d in if statement?
Yup - Math.Sign() is documented to return 0 if the double value is 0
(and positive zero is equal to negative zero according to the IEEE spec).
To determine if you have negative zero, I think you'll have to write a
bit of code that looks at the sign bit directly:
public static bool IsSignBitSet( double x) {
byte[] bytes = BitConverter.GetBytes( x);
// this assumes a little-endian machine
return ((bytes[bytes.Length-1] & 0x80) == 0x80);
}
// ...
Console.WriteLine( "IsSignBitSet( +0.0): {0}", IsSignBitSet( +0.0));
Console.WriteLine( "IsSignBitSet( -0.0): {0}", IsSignBitSet( -0.0));
The above code outputs:
IsSignBitSet( +0.0): False
IsSignBitSet( -0.0): True
--
mikeb
mikeb <ma************@nospam.mailnull.com> wrote: How to differentiate -0.0d & 0.0d in if statement?
Yup - Math.Sign() is documented to return 0 if the double value is 0 (and positive zero is equal to negative zero according to the IEEE spec).
To determine if you have negative zero, I think you'll have to write a bit of code that looks at the sign bit directly:
Alternatively, check for whether it's equal to positive 0 but has a
different bit sequence to positive 0 (still using
BitConverter.GetBytes, but regardless of endianness).
--
Jon Skeet - <sk***@pobox.com> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Frank Oquendo <no******@here.com> wrote: How to differentiate -0.0d & 0.0d in if statement?
How can a sign have any meaning when discussing the absence of a value?
Very easily. -0 and +0 are mathematically distinct when considering
limits, where something can tend to 0 from above or below, for
instance. It's all well-defined in IEEE arithmetic, I believe.
--
Jon Skeet - <sk***@pobox.com> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Jon Skeet [C# MVP] wrote: mikeb <ma************@nospam.mailnull.com> wrote:
How to differentiate -0.0d & 0.0d in if statement?
Yup - Math.Sign() is documented to return 0 if the double value is 0 (and positive zero is equal to negative zero according to the IEEE spec).
To determine if you have negative zero, I think you'll have to write a bit of code that looks at the sign bit directly:
Alternatively, check for whether it's equal to positive 0 but has a different bit sequence to positive 0 (still using BitConverter.GetBytes, but regardless of endianness).
Alright - in the interest of endian-safeness, here's an alternative:
private readonly static long signBit =
BitConverter.DoubleToInt64Bits( -0.0);
public static bool IsSignBitSet( double x) {
long bits = BitConverter.DoubleToInt64Bits( x);
return( (bits & signBit) != 0);
}
--
mikeb
Hi Mikeb,
But compact C# doesn't have " BitConverter.DoubleToInt64Bits()" functionality?
"mikeb" wrote: Jon Skeet [C# MVP] wrote: mikeb <ma************@nospam.mailnull.com> wrote:
How to differentiate -0.0d & 0.0d in if statement?
Yup - Math.Sign() is documented to return 0 if the double value is 0 (and positive zero is equal to negative zero according to the IEEE spec).
To determine if you have negative zero, I think you'll have to write a bit of code that looks at the sign bit directly:
Alternatively, check for whether it's equal to positive 0 but has a different bit sequence to positive 0 (still using BitConverter.GetBytes, but regardless of endianness).
Alright - in the interest of endian-safeness, here's an alternative:
private readonly static long signBit = BitConverter.DoubleToInt64Bits( -0.0);
public static bool IsSignBitSet( double x) { long bits = BitConverter.DoubleToInt64Bits( x);
return( (bits & signBit) != 0); }
-- mikeb
Avin Patel <Av*******@discussions.microsoft.com> wrote: But compact C# doesn't have " BitConverter.DoubleToInt64Bits()" functionality?
In that case, you can use BitConverter.GetBytes and just compare the
contents of the returned array with BitConverter.GetBytes(0d).
--
Jon Skeet - <sk***@pobox.com> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Hi,
I guess this should be ok for compact case:
static public bool IsMinusZero(double data)
{
byte[] minuszero =
BitConverter.GetBytes(-0.0);
byte[] bytes = BitConverter.GetBytes(data);
for(int i=0; i<minuszero.Length; i++) {
if(bytes[i] != minuszero[i]) { return false; }
}
return true;
}
Thanks for replies,
Avin Patel
"Avin Patel" wrote: Hi Mikeb, But compact C# doesn't have " BitConverter.DoubleToInt64Bits()" functionality? "mikeb" wrote:
Jon Skeet [C# MVP] wrote: mikeb <ma************@nospam.mailnull.com> wrote:
>>How to differentiate -0.0d & 0.0d in if statement? > >Yup - Math.Sign() is documented to return 0 if the double value is 0 >(and positive zero is equal to negative zero according to the IEEE spec). > >To determine if you have negative zero, I think you'll have to write a >bit of code that looks at the sign bit directly:
Alternatively, check for whether it's equal to positive 0 but has a different bit sequence to positive 0 (still using BitConverter.GetBytes, but regardless of endianness).
Alright - in the interest of endian-safeness, here's an alternative:
private readonly static long signBit = BitConverter.DoubleToInt64Bits( -0.0);
public static bool IsSignBitSet( double x) { long bits = BitConverter.DoubleToInt64Bits( x);
return( (bits & signBit) != 0); }
-- mikeb This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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