From 4c96c9343c9d1738e1eec4405bc3f52bcaf56e30 Mon Sep 17 00:00:00 2001
From: Cat Stevens <catb0t@protonmail.ch>
Date: Thu, 22 Mar 2018 17:13:47 -0400
Subject: [PATCH] basis/math: add logn to math.functions (fix #1981)

---
 basis/math/functions/functions-docs.factor  | 4 ++++
 basis/math/functions/functions-tests.factor | 4 ++++
 basis/math/functions/functions.factor       | 3 +++
 3 files changed, 11 insertions(+)

diff --git a/basis/math/functions/functions-docs.factor b/basis/math/functions/functions-docs.factor
index 6c1930b463..02c4da0d12 100644
--- a/basis/math/functions/functions-docs.factor
+++ b/basis/math/functions/functions-docs.factor
@@ -117,6 +117,10 @@ HELP: log
 { $values { "x" number } { "y" number } }
 { $description "Natural logarithm function. Outputs negative infinity if " { $snippet "x" } " is 0." } ;
 
+HELP: logn
+{ $values { "x" number } { "n" number } { "y" number } }
+{ $description "Finds the base " { $snippet "n" } " logarithm of " { $snippet "x" } "." } ;
+
 HELP: log1+
 { $values { "x" number } { "y" number } }
 { $description "Takes the natural logarithm of " { $snippet "1 + x" } ". Outputs negative infinity if " { $snippet "1 + x" } " is zero. This word may be more accurate than " { $snippet "1 + log" } " for very small values of " { $snippet "x" } "." } ;
diff --git a/basis/math/functions/functions-tests.factor b/basis/math/functions/functions-tests.factor
index bc468931e1..da9630d33f 100644
--- a/basis/math/functions/functions-tests.factor
+++ b/basis/math/functions/functions-tests.factor
@@ -69,6 +69,10 @@ IN: math.functions.tests
 { 0.0 } [ 1.0 log ] unit-test
 { 1.0 } [ e log ] unit-test
 
+{ 0.0 } [ 1 e logn ] unit-test
+{ 0.0 } [ 1.0 e logn ] unit-test
+{ 1.0 } [ e e logn ] unit-test
+
 CONSTANT: log-factorial-1000 0x1.71820d04e2eb6p12
 CONSTANT: log10-factorial-1000 0x1.40f3593ed6f8ep11
 
diff --git a/basis/math/functions/functions.factor b/basis/math/functions/functions.factor
index 010420a66f..aa26be21a9 100644
--- a/basis/math/functions/functions.factor
+++ b/basis/math/functions/functions.factor
@@ -196,6 +196,9 @@ M: real log >float log ; inline
 
 M: complex log >polar [ flog ] dip rect> ; inline
 
+: logn ( x n -- y )
+  [ log ] bi@ / ;
+
 <PRIVATE
 
 : most-negative-finite-float ( -- x )