feat: initial release

Assisted-by: GLM 5.3 Flash

internal/core/cumprod_half_test.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+// SPDX-License-Identifier: MIT
+
+package core
+
+import "testing"
+
+// TestCumProdHalfNarrowsCarryPerStep pins the float16 cumulative
+// product's carry discipline: every step narrows the running product to
+// half before combining, exactly as the stored element narrows, so each
+// step multiplies the rounded carry. The input 67, 65, 6 makes the
+// discipline visible: 67 times 65 is 4355 in float64, which narrows to
+// 4356, and 4356 times 6 rounds to 26144; a carry left in float64 would
+// give 4355 times 6 = 26130, which rounds to 26128.
+func TestCumProdHalfNarrowsCarryPerStep(t *testing.T) {
+	a := mustFromHalves(t, []uint16{
+		HalfFromFloat64(67), HalfFromFloat64(65), HalfFromFloat64(6),
+	}, 3)
+	out, err := CumProd(a, 0)
+	if err != nil {
+		t.Fatalf("CumProd: %v", err)
+	}
+	want := []float64{67, 4356, 26144}
+	for i, w := range want {
+		if got := HalfToFloat64(out.RawHalves()[i]); got != w {
+			t.Fatalf("element %d = %v, want %v", i, got, w)
+		}
+	}
+}