math.ilogb Method (Double)

mathilogb Method (Double)

Gets the unbiased exponent of the specified floating-point number.

Namespace: C
Assembly: C.math (in C.math.dll) Version: 1.0.0.0 (1.0.0.0)

Syntax

public static int ilogb(
	double number
)

Public Shared Function ilogb ( 
	number As Double
) As Integer

public:
static int ilogb(
	double number
)

static member ilogb : 
        number : float -> int

Parameters

number: Type: SystemDouble
A floating-point number.

Return Value

Type: Int32
The unbiased exponent of the specified floating-point number, or a special value if number is not normal or subnormal.

Remarks

The unbiased exponent is the integral part of the logarithm base 2 of number. The unbiased exponent is such that:

number = significand(number) * 2^ilogb(number).

The return unbiased exponent is valid for all normal and subnormal numbers. Special values are treated as follows.

If number is ±0, FP_ILOGB0 is returned.
If number is infinite, INT_MAX is returned.
If number is NaN, FP_ILOGBNAN is returned.

If number is not zero, infinite, or NaN, the value returned is exactly equivalent to (Int32)logb(number).

The value of the exponent returned by ilogb(Double) is always 1 less than the exponent retuned by frexp(Double, Int32) because of the different normalization requirements: for ilogb(Double), the normalized significand is in the interval [1, 2), but for frexp(Double, Int32), the normalized significand is in the interval [0.5, 1).

See ilogb in the C standard documentation.

Examples

C++

Copy

Assert.IsTrue(math.ilogb(1D) == 0);
Assert.IsTrue(math.ilogb(System.Math.E) == 1);
Assert.IsTrue(math.ilogb(1024D) == 10);
Assert.IsTrue(math.ilogb(-2000D) == 10);

Assert.IsTrue(math.ilogb(2D) == 1);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 56D)) == 56);
Assert.IsTrue(math.ilogb(1.1D * Math.Pow(2D, -1074D)) == -1074);
Assert.IsTrue(math.ilogb(Math.Pow(2D, -1075D)) == math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 1024D)) == math.INT_MAX);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 1023D)) == 1023);
Assert.IsTrue(math.ilogb(2D * Math.Pow(2D, 102D)) == 103);

Assert.IsTrue(math.ilogb(math.DBL_DENORM_MIN) == math.DBL_EXP_MIN - math.DBL_MANT_BITS);
Assert.IsTrue(math.ilogb(math.DBL_DENORM_MAX) == math.DBL_EXP_MIN - 1);
Assert.IsTrue(math.ilogb(math.DBL_MIN) == math.DBL_EXP_MIN);
Assert.IsTrue(math.ilogb(math.DBL_MAX) == math.DBL_EXP_MAX);

Assert.IsTrue(math.ilogb(System.Double.PositiveInfinity) == math.INT_MAX);
Assert.IsTrue(math.ilogb(System.Double.NegativeInfinity) == math.INT_MAX);
Assert.IsTrue(math.ilogb(0D) == math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(-0D) == math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(System.Double.NaN) == math.FP_ILOGBNAN);
Assert.IsTrue(math.ilogb(-System.Double.NaN) == math.FP_ILOGBNAN);

Assert.IsTrue(math.ilogb(1D) = 0);
Assert.IsTrue(math.ilogb(System.Math.E) = 1);
Assert.IsTrue(math.ilogb(1024D) = 10);
Assert.IsTrue(math.ilogb(-2000D) = 10);

Assert.IsTrue(math.ilogb(2D) = 1);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 56D)) = 56);
Assert.IsTrue(math.ilogb(1.1D * Math.Pow(2D, -1074D)) = -1074);
Assert.IsTrue(math.ilogb(Math.Pow(2D, -1075D)) = math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 1024D)) = math.INT_MAX);
Assert.IsTrue(math.ilogb(Math.Pow(2D, 1023D)) = 1023);
Assert.IsTrue(math.ilogb(2D * Math.Pow(2D, 102D)) = 103);

Assert.IsTrue(math.ilogb(math.DBL_DENORM_MIN) = math.DBL_EXP_MIN - math.DBL_MANT_BITS);
Assert.IsTrue(math.ilogb(math.DBL_DENORM_MAX) = math.DBL_EXP_MIN - 1);
Assert.IsTrue(math.ilogb(math.DBL_MIN) = math.DBL_EXP_MIN);
Assert.IsTrue(math.ilogb(math.DBL_MAX) = math.DBL_EXP_MAX);

Assert.IsTrue(math.ilogb(System.Double.PositiveInfinity) = math.INT_MAX);
Assert.IsTrue(math.ilogb(System.Double.NegativeInfinity) = math.INT_MAX);
Assert.IsTrue(math.ilogb(0D) = math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(-0D) = math.FP_ILOGB0);
Assert.IsTrue(math.ilogb(System.Double.NaN) = math.FP_ILOGBNAN);
Assert.IsTrue(math.ilogb(-System.Double.NaN) = math.FP_ILOGBNAN);

Reference

math Class

ilogb Overload

C Namespace