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