From 9e333e5058f54703fa9be0f34914061be6c8a272 Mon Sep 17 00:00:00 2001
From: Emanuel <emanuel@empa.xyz>
Date: Wed, 6 Dec 2023 14:32:56 +0100
Subject: [PATCH] Add calc.root function (#2736)

Fixes #2522
---
 crates/typst/src/foundations/calc.rs | 32 ++++++++++++++++++++++++++++
 tests/typ/compute/calc.typ           | 16 ++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/crates/typst/src/foundations/calc.rs b/crates/typst/src/foundations/calc.rs
index 597bf156b..c65102ced 100644
--- a/crates/typst/src/foundations/calc.rs
+++ b/crates/typst/src/foundations/calc.rs
@@ -17,6 +17,7 @@ pub fn module() -> Module {
     scope.define_func::<pow>();
     scope.define_func::<exp>();
     scope.define_func::<sqrt>();
+    scope.define_func::<root>();
     scope.define_func::<sin>();
     scope.define_func::<cos>();
     scope.define_func::<tan>();
@@ -183,6 +184,37 @@ pub fn sqrt(
     Ok(value.v.float().sqrt())
 }
 
+/// Calculates the real nth root of a number.
+///
+/// If the number is negative, then n must be odd.
+///
+/// ```example
+/// #calc.root(16.0, 4) \
+/// #calc.root(27.0, 3)
+/// ```
+#[func]
+pub fn root(
+    /// The expression to take the root of
+    radicand: f64,
+    /// Which root of the radicand to take
+    index: Spanned<i64>,
+) -> SourceResult<f64> {
+    if index.v == 0 {
+        bail!(index.span, "cannot take the 0th root of a number");
+    } else if radicand < 0.0 {
+        if index.v % 2 == 0 {
+            bail!(
+                index.span,
+                "negative numbers do not have a real nth root when n is even"
+            );
+        } else {
+            Ok(-(-radicand).powf(1.0 / index.v as f64))
+        }
+    } else {
+        Ok(radicand.powf(1.0 / index.v as f64))
+    }
+}
+
 /// Calculates the sine of an angle.
 ///
 /// When called with an integer or a float, they will be interpreted as
diff --git a/tests/typ/compute/calc.typ b/tests/typ/compute/calc.typ
index 86dcafcdb..e61e15d47 100644
--- a/tests/typ/compute/calc.typ
+++ b/tests/typ/compute/calc.typ
@@ -162,6 +162,22 @@
 // Error: 12-14 cannot take square root of negative number
 #calc.sqrt(-1)
 
+---
+#test(calc.root(12.0, 1), 12.0)
+#test(calc.root(9.0, 2), 3.0)
+#test(calc.root(27.0, 3), 3.0)
+#test(calc.root(-27.0, 3), -3.0)
+// 100^(-1/2) = (100^(1/2))^-1 = 1/sqrt(100)
+#test(calc.root(100.0, -2), 0.1)
+
+---
+// Error: 17-18 cannot take the 0th root of a number
+#calc.root(1.0, 0)
+
+---
+// Error: 24-25 negative numbers do not have a real nth root when n is even
+#test(calc.root(-27.0, 4), -3.0)
+
 ---
 // Error: 11-13 value must be strictly positive
 #calc.log(-1)