floor

import std.math.traits : isNaN;

assert(floor(+123.456L) == +123);
assert(floor(-123.456L) == -124);
assert(floor(+123.0L) == +123);
assert(floor(-124.0L) == -124);
assert(floor(-1.234L) == -2);
assert(floor(-0.123L) == -1);
assert(floor(0.0L) == 0);
assert(floor(+0.123L) == 0);
assert(floor(+1.234L) == 1);
assert(floor(real.infinity) == real.infinity);
assert(isNaN(floor(real.nan)));
assert(isNaN(floor(real.init)));