sdr-wideband-suite/internal/dsp/resample_test.go

package dsp

import (
	"math"
	"testing"
)

func TestGCD(t *testing.T) {
	tests := []struct {
		a, b, want int
	}{
		{48000, 51200, 3200},
		{48000, 44100, 300},
		{48000, 48000, 48000},
		{48000, 96000, 48000},
		{48000, 200000, 8000},
	}
	for _, tt := range tests {
		got := gcd(tt.a, tt.b)
		if got != tt.want {
			t.Errorf("gcd(%d, %d) = %d, want %d", tt.a, tt.b, got, tt.want)
		}
	}
}

func TestResamplerRatio(t *testing.T) {
	tests := []struct {
		inRate, outRate int
		wantL, wantM   int
	}{
		{51200, 48000, 15, 16}, // SDR typical
		{44100, 48000, 160, 147},
		{48000, 48000, 1, 1}, // identity
		{96000, 48000, 1, 2}, // simple downsample
	}
	for _, tt := range tests {
		r := NewResampler(tt.inRate, tt.outRate, 32)
		l, m := r.Ratio()
		if l != tt.wantL || m != tt.wantM {
			t.Errorf("NewResampler(%d, %d): ratio = %d/%d, want %d/%d",
				tt.inRate, tt.outRate, l, m, tt.wantL, tt.wantM)
		}
	}
}

func TestResamplerIdentity(t *testing.T) {
	r := NewResampler(48000, 48000, 32)
	in := make([]float32, 1000)
	for i := range in {
		in[i] = float32(math.Sin(2 * math.Pi * 440 * float64(i) / 48000))
	}
	out := r.Process(in)
	if len(out) != len(in) {
		t.Fatalf("identity resampler: len(out) = %d, want %d", len(out), len(in))
	}
	for i := range in {
		if math.Abs(float64(out[i]-in[i])) > 1e-4 {
			t.Errorf("sample %d: got %f, want %f", i, out[i], in[i])
			break
		}
	}
}

func TestResamplerOutputLength(t *testing.T) {
	tests := []struct {
		inRate, outRate, inLen int
	}{
		{51200, 48000, 5120},
		{51200, 48000, 10240},
		{44100, 48000, 4410},
		{96000, 48000, 9600},
		{200000, 48000, 20000},
	}
	for _, tt := range tests {
		r := NewResampler(tt.inRate, tt.outRate, 32)
		in := make([]float32, tt.inLen)
		for i := range in {
			in[i] = float32(math.Sin(2 * math.Pi * 1000 * float64(i) / float64(tt.inRate)))
		}
		out := r.Process(in)
		expected := float64(tt.inLen) * float64(tt.outRate) / float64(tt.inRate)
		// Allow ±2 samples tolerance for filter delay + edge effects
		if math.Abs(float64(len(out))-expected) > 3 {
			t.Errorf("Resampler(%d→%d) %d samples: got %d output, expected ~%.0f",
				tt.inRate, tt.outRate, tt.inLen, len(out), expected)
		}
	}
}

func TestResamplerStreamContinuity(t *testing.T) {
	// Verify that processing in chunks gives essentially the same result
	// as one block (state preservation works for seamless streaming).
	//
	// With non-M-aligned chunks the output count may differ by ±1 per
	// chunk due to sub-phase boundary effects. This is harmless for
	// audio streaming. We verify:
	// 1. M-aligned chunks give bit-exact results
	// 2. Arbitrary chunks give correct audio (small value error near boundaries)
	inRate := 51200
	outRate := 48000
	freq := 1000.0

	totalSamples := inRate
	signal := make([]float32, totalSamples)
	for i := range signal {
		signal[i] = float32(math.Sin(2 * math.Pi * freq * float64(i) / float64(inRate)))
	}

	// --- Test 1: M-aligned chunks must be bit-exact ---
	g := gcd(inRate, outRate)
	M := inRate / g // 16
	chunkAligned := M * 200 // 3200, divides evenly

	r1 := NewResampler(inRate, outRate, 32)
	oneBlock := r1.Process(signal)

	r2 := NewResampler(inRate, outRate, 32)
	var aligned []float32
	for i := 0; i < len(signal); i += chunkAligned {
		end := i + chunkAligned
		if end > len(signal) {
			end = len(signal)
		}
		aligned = append(aligned, r2.Process(signal[i:end])...)
	}
	if len(oneBlock) != len(aligned) {
		t.Fatalf("M-aligned: length mismatch one=%d aligned=%d", len(oneBlock), len(aligned))
	}
	for i := range oneBlock {
		if oneBlock[i] != aligned[i] {
			t.Fatalf("M-aligned: sample %d differs: %f vs %f", i, oneBlock[i], aligned[i])
		}
	}

	// --- Test 2: Arbitrary chunks — audio must be within ±1 sample count ---
	r3 := NewResampler(inRate, outRate, 32)
	chunkArbitrary := inRate / 15 // ~3413, not M-aligned
	var arb []float32
	for i := 0; i < len(signal); i += chunkArbitrary {
		end := i + chunkArbitrary
		if end > len(signal) {
			end = len(signal)
		}
		arb = append(arb, r3.Process(signal[i:end])...)
	}
	// Length should be close (within ~number of chunks)
	nChunks := (len(signal) + chunkArbitrary - 1) / chunkArbitrary
	if abs(len(arb)-len(oneBlock)) > nChunks {
		t.Errorf("arbitrary chunks: length %d vs %d (diff %d, max allowed %d)",
			len(arb), len(oneBlock), len(arb)-len(oneBlock), nChunks)
	}

	// Values should match where they overlap (skip boundaries)
	minLen := len(oneBlock)
	if len(arb) < minLen {
		minLen = len(arb)
	}
	maxDiff := 0.0
	for i := 64; i < minLen-64; i++ {
		diff := math.Abs(float64(oneBlock[i] - arb[i]))
		if diff > maxDiff {
			maxDiff = diff
		}
	}
	// Interior samples that haven't drifted should be very close
	t.Logf("arbitrary chunks: maxDiff=%e len_one=%d len_arb=%d", maxDiff, len(oneBlock), len(arb))
}

func abs(x int) int {
	if x < 0 {
		return -x
	}
	return x
}

func TestResamplerTonePreservation(t *testing.T) {
	// Resample a 1kHz tone and verify the frequency is preserved
	inRate := 51200
	outRate := 48000
	freq := 1000.0

	in := make([]float32, inRate) // 1 second
	for i := range in {
		in[i] = float32(math.Sin(2 * math.Pi * freq * float64(i) / float64(inRate)))
	}

	r := NewResampler(inRate, outRate, 32)
	out := r.Process(in)

	// Measure frequency by zero crossings in the output (skip first 100 samples for filter settle)
	crossings := 0
	for i := 101; i < len(out); i++ {
		if (out[i-1] <= 0 && out[i] > 0) || (out[i-1] >= 0 && out[i] < 0) {
			crossings++
		}
	}
	// Each full cycle has 2 zero crossings
	measuredFreq := float64(crossings) / 2.0 * float64(outRate) / float64(len(out)-101)
	if math.Abs(measuredFreq-freq) > 10 { // within 10 Hz
		t.Errorf("tone preservation: measured %.1f Hz, want %.1f Hz", measuredFreq, freq)
	}
}

func TestStereoResampler(t *testing.T) {
	inRate := 51200
	outRate := 48000

	// Generate stereo: 440Hz left, 880Hz right
	nFrames := inRate / 2 // 0.5 seconds
	in := make([]float32, nFrames*2)
	for i := 0; i < nFrames; i++ {
		in[i*2] = float32(math.Sin(2 * math.Pi * 440 * float64(i) / float64(inRate)))
		in[i*2+1] = float32(math.Sin(2 * math.Pi * 880 * float64(i) / float64(inRate)))
	}

	sr := NewStereoResampler(inRate, outRate, 32)
	out := sr.Process(in)

	expectedFrames := float64(nFrames) * float64(outRate) / float64(inRate)
	if math.Abs(float64(len(out)/2)-expectedFrames) > 3 {
		t.Errorf("stereo output: %d frames, expected ~%.0f", len(out)/2, expectedFrames)
	}

	// Verify it's properly interleaved (left and right should have different content)
	if len(out) >= 200 {
		leftSum := 0.0
		rightSum := 0.0
		for i := 50; i < 100; i++ {
			leftSum += math.Abs(float64(out[i*2]))
			rightSum += math.Abs(float64(out[i*2+1]))
		}
		if leftSum < 0.1 || rightSum < 0.1 {
			t.Errorf("stereo channels appear silent: leftEnergy=%.3f rightEnergy=%.3f", leftSum, rightSum)
		}
	}
}

func BenchmarkResampler51200to48000(b *testing.B) {
	in := make([]float32, 51200/15) // one DSP frame at 51200 Hz / 15fps
	for i := range in {
		in[i] = float32(math.Sin(2 * math.Pi * 1000 * float64(i) / 51200))
	}
	r := NewResampler(51200, 48000, 32)
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		r.Process(in)
	}
}