From 47c773300a40adf66e59e83ca2492f87b7ccb57d Mon Sep 17 00:00:00 2001
From: PowerUser64 <dev@blake.ly>
Date: Thu, 27 Nov 2025 00:31:33 -0800
Subject: [PATCH] feat(math): add `logb` function

Closes #12112
---
 CHANGELOG.rst          |  4 ++++
 doc_src/cmds/math.rst  |  2 ++
 src/tinyexpr.rs        |  1 +
 tests/checks/math.fish | 15 +++++++++++++++
 4 files changed, 22 insertions(+)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 80e8dcc25..fc78be460 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,10 @@ Notable improvements and fixes
 Deprecations and removed features
 ---------------------------------
 
+Scripting improvements
+----------------------
+- ``math`` gained a new ``logb`` function.
+
 Interactive improvements
 ------------------------
 - When typing immediately after starting fish, the first prompt is now rendered correctly.
diff --git a/doc_src/cmds/math.rst b/doc_src/cmds/math.rst
index 3fffcbe6b..4fc886a91 100644
--- a/doc_src/cmds/math.rst
+++ b/doc_src/cmds/math.rst
@@ -156,6 +156,8 @@ Functions
     the base-10 logarithm
 ``log2``
     the base-2 logarithm
+``logb(b,x)``
+    returns the logarithm with base b of x
 ``max``
     returns the largest of the given numbers - this takes an arbitrary number of arguments (but at least one)
 ``min``
diff --git a/src/tinyexpr.rs b/src/tinyexpr.rs
index befb02240..13e8e08af 100644
--- a/src/tinyexpr.rs
+++ b/src/tinyexpr.rs
@@ -291,6 +291,7 @@ fn npr(n: f64, r: f64) -> f64 {
     (L!("log"), Function::Fn1(f64::log10)),
     (L!("log10"), Function::Fn1(f64::log10)),
     (L!("log2"), Function::Fn1(f64::log2)),
+    (L!("logb"), Function::Fn2(|base, x| x.log(base))),
     (L!("max"), Function::FnN(maximum)),
     (L!("min"), Function::FnN(minimum)),
     (L!("ncr"), Function::Fn2(ncr)),
diff --git a/tests/checks/math.fish b/tests/checks/math.fish
index cb2c4bec3..9da01e2fa 100644
--- a/tests/checks/math.fish
+++ b/tests/checks/math.fish
@@ -276,6 +276,21 @@ echo $status
 math 'log2(8)'
 # CHECK: 3
 
+math 'logb(2, 8)'
+# CHECK: 3
+math 'logb(67, 406067677556641)'
+# CHECK: 8
+math 'logb(42, 230539333248)'
+# CHECK: 7
+math 'logb(12, 8916100448256)'
+# CHECK: 12
+math 'logb(3, 5559060566555523)'
+# CHECK: 33
+math 'logb(5, 2384185791015625)'
+# CHECK: 22
+math 'logb(7, 343)'
+# CHECK: 3
+
 # same as sin(cos(2 x pi))
 math sin cos 2 x pi
 # CHECK: 0.841471