// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

package core

import "testing"

// TestWhereHalfCanonicalisesNaN pins the float16 fast path of Where:
// every selected half value narrows through HalfFromFloat64 on the way
// out, so a NaN loses its payload and lands as the canonical 0x7E00 with
// its sign kept, while every finite value survives the round trip bit
// for bit. A payload copy would leak the incoming patterns 0x7C01 and
// 0x7D00 instead.
func TestWhereHalfCanonicalisesNaN(t *testing.T) {
	cond := mustFromInts(t, []int64{1, 0, 1, 0}, 4)
	// x: a signalling NaN with payload, 2, a negative signalling NaN, and
	// a slot the condition does not pick. y: 4, 3, 4 and -1.
	x := mustFromHalves(t, []uint16{0x7C01, 0x4000, 0xFE01, 0x3C00}, 4)
	y := mustFromHalves(t, []uint16{0x4400, 0x4200, 0x4400, 0xBC00}, 4)
	out, err := Where(cond, x, y)
	if err != nil {
		t.Fatalf("Where: %v", err)
	}
	if out.Dtype() != Float16 {
		t.Fatalf("Where answered dtype %s, want float16", out.Dtype())
	}
	want := []uint16{0x7E00, 0x4200, 0xFE00, 0xBC00}
	got := out.RawHalves()
	for i, w := range want {
		if got[i] != w {
			t.Fatalf("element %d = %#04x, want %#04x", i, got[i], w)
		}
	}
}