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Function std.math.exponential.logb

Extracts the exponent of x as a signed integral value.

real logb (
  real x
) pure nothrow @nogc @trusted;

double logb (
  double x
) pure nothrow @nogc @trusted;

float logb (
  float x
) pure nothrow @nogc @trusted;

If x is subnormal, it is treated as if it were normalized. For a positive, finite x:

1 <= x * FLT_RADIX-logb(x) < FLT_RADIX

Special Values
x logb(x) divide by 0?
±∞ +∞ no
±0.0 -∞ yes


writeln(logb(1.0)); // 0
writeln(logb(100.0)); // 6

writeln(logb(0.0)); // -real.infinity
writeln(logb(real.infinity)); // real.infinity
writeln(logb(-real.infinity)); // real.infinity


Walter Bright, Don Clugston, Conversion of CEPHES math library to D by Iain Buclaw and David Nadlinger


Boost License 1.0.