Implement the cross product function for JS and RS

alantech · Nov 23, 2024 · 210f7d3 · 210f7d3
1 parent 7d8ec1c
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diff --git a/alan_std.js b/alan_std.js
@@ -420,6 +420,16 @@ export class Str {
   }
 }
 
+export function cross(a, b) {
+  // Assuming they're all the same type
+  let type = a[0].constructor;
+  return [
+    new type(a[1].val * b[2].val - a[2].val * b[1].val),
+    new type(a[2].val * b[0].val - a[0].val * b[2].val),
+    new type(a[0].val * b[1].val - a[1].val * b[0].val),
+  ];
+}
+
 export class GPU {
   constructor(adapter, device, queue) {
     this.adapter = adapter;

diff --git a/alan_std.test.js b/alan_std.test.js
@@ -411,3 +411,15 @@ assert.equal(new alanStd.I64(1).ctz(), 0n, "ctzI64(1) = 0");
 assert.equal(new alanStd.I64(2).ctz(), 1n, "ctzI64(2) = 1");
 assert.equal(new alanStd.I64(3).ctz(), 0n, "ctzI64(3) = 0");
 assert.equal(new alanStd.I64(-9_223_372_036_854_775_808n).ctz(), 63n, "ctzI64(-9_223_372_036_854_775_808n) = 63");
+
+assert.deepEqual(alanStd.cross(
+  [new alanStd.F64(1), new alanStd.F64(0), new alanStd.F64(0)],
+  [new alanStd.F64(0), new alanStd.F64(1), new alanStd.F64(0)],
+), [new alanStd.F64(0), new alanStd.F64(0), new alanStd.F64(1)],
+"cross([1, 0, 0], [0, 1, 0]) = [0, 0, 1]");
+
+assert.deepEqual(alanStd.cross(
+  [new alanStd.F64(0), new alanStd.F64(1), new alanStd.F64(0)],
+  [new alanStd.F64(1), new alanStd.F64(0), new alanStd.F64(0)],
+), [new alanStd.F64(0), new alanStd.F64(0), new alanStd.F64(-1)],
+"cross([0, 1, 0], [1, 0, 0]) = [0, 0, -1]");
diff --git a/alan_std/src/lib.rs b/alan_std/src/lib.rs
@@ -690,6 +690,20 @@ pub fn productset<V: std::clone::Clone + std::hash::Hash + Eq>(
     out
 }
 
+/// Vector-related functions
+
+pub fn cross<V>(a: &[V; 3], b: &[V; 3]) -> [V; 3]
+where
+    V: std::ops::Deref + std::ops::Mul<Output = V> + std::ops::Sub<Output = V>,
+    <V as Deref>::Target: std::ops::Mul<Output = V> + Sized + Copy + std::ops::Sub<Output = V>,
+{
+    [
+        *a[1] * *b[2] - *a[2] * *b[1],
+        *a[2] * *b[0] - *a[0] * *b[2],
+        *a[0] * *b[1] - *a[1] * *b[0],
+    ]
+}
+
 /// GPU-related functions and types
 
 pub struct GPU {