Issue #21527 has been updated by Eregon (Benoit Daloze). ```ruby require 'fiddle' log1p = Fiddle::Function.new(Fiddle.dlopen(nil)["log1p"], [Fiddle::TYPE_DOUBLE], Fiddle::TYPE_DOUBLE) p log1p.call(1.0e-16) # => 1.0e-16 ``` ---------------------------------------- Feature #21527: Proposal: Math.log1p and Math.expm1 https://bugs.ruby-lang.org/issues/21527#change-114226 * Author: mame (Yusuke Endoh) * Status: Open ---------------------------------------- Let's add `Math.log1p` and `Math.expm1`. * `Math.log1p(x)`: Computes `Math.log(x + 1)` * `Math.expm1(x)`: Computes `Math.exp(x) - 1` These methods are often more accurate than the straightforward computation, especially when `x` is close to zero. ``` # The current approach loses precision p Math.log(1 + 1.0e-16) #=> 0.0 p Math.exp(1.0e-16) - 1 #=> 0.0 # The proposed methods return the accurate result p Math.log1p(1.0e-16) #=> 1.0e-16 p Math.expm1(1.0e-16) #=> 1.0e-16 ``` Note that they are very standard; the C99 even defines `log1p()` and `expm1()`. Other major programming languages (Python, JavaScript, Java, Go, Rust, etc.) also provide them. PR: https://github.com/ruby/ruby/pull/14087 -- https://bugs.ruby-lang.org/