nextDown

fnreal nextDown(real x) @safe pure nothrow @nogc

Calculate the next smallest floating point value before x.

Return the greatest number less than x that is representable as a real; thus, it gives the previous point on the IEEE number line.

x, nextDown(x) ∞, real.max ±0.0, -real.min_normal*real.epsilon -real.max, -∞ -∞, -∞ NaN, NaN
fndouble nextDown(double x) @safe pure nothrow @nogc

ditto

fnfloat nextDown(float x) @safe pure nothrow @nogc

ditto