dsp/window: add lookup table window functions

dsp/window/window.go

@@ -323,3 +323,32 @@ func Gaussian(seq []float64, sigma float64) []float64 {
 	}
 	return seq
 }
+
+// Values is an arbitrary real window function.
+type Values []float64
+
+// NewValues returns a Values of length n with weights corresponding to the
+// provided window function.
+func NewValues(window func([]float64) []float64, n int) Values {
+	v := make(Values, n)
+	for i := range v {
+		v[i] = 1
+	}
+	return window(v)
+}
+
+// Transform applies the weights in the receiver to seq in place, returning the
+// result. If v is nil, Transform is a no-op, otherwise the length of v must
+// match the length of seq.
+func (v Values) Transform(seq []float64) []float64 {
+	if v == nil {
+		return seq
+	}
+	if len(v) != len(seq) {
+		panic("window: length mismatch")
+	}
+	for i, w := range v {
+		seq[i] *= w
+	}
+	return seq
+}

dsp/window/window_complex.go

@@ -323,3 +323,32 @@ func GaussianComplex(seq []complex128, sigma float64) []complex128 {
 	}
 	return seq
 }
+
+// ValuesComplex is an arbitrary complex window function.
+type ValuesComplex []complex128
+
+// NewValuesComplex returns a ValuesComplex of length n with weights corresponding
+// to the provided window function.
+func NewValuesComplex(window func([]complex128) []complex128, n int) ValuesComplex {
+	v := make(ValuesComplex, n)
+	for i := range v {
+		v[i] = 1
+	}
+	return window(v)
+}
+
+// Transform applies the weights in the receiver to seq in place, returning the
+// result. If v is nil, Transform is a no-op, otherwise the length of v must
+// match the length of seq.
+func (v ValuesComplex) Transform(seq []complex128) []complex128 {
+	if v == nil {
+		return seq
+	}
+	if len(v) != len(seq) {
+		panic("window: length mismatch")
+	}
+	for i, w := range v {
+		seq[i] *= w
+	}
+	return seq
+}

dsp/window/window_example_test.go

@@ -103,3 +103,18 @@ func ExampleHamming() {
 	// srcCpy: [0.092577 0.136714 0.220669 0.336222 0.472063 0.614894 0.750735 0.866288 0.950242 0.994379 0.994379 0.950242 0.866288 0.750735 0.614894 0.472063 0.336222 0.220669 0.136714 0.092577]
 	// dst:    [0.092577 0.136714 0.220669 0.336222 0.472063 0.614894 0.750735 0.866288 0.950242 0.994379 0.994379 0.950242 0.866288 0.750735 0.614894 0.472063 0.336222 0.220669 0.136714 0.092577]
 }
+
+func ExampleValues() {
+	src := []float64{1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+		1, 1, 1, 1, 1, 1, 1, 1, 1, 1}
+
+	// Create a Sine Window lookup table.
+	sine := window.NewValues(window.Sine, len(src))
+
+	// Apply the transformation to the src.
+	fmt.Printf("dst: %f\n", sine.Transform(src))
+
+	// Output:
+	//
+	// dst: [0.078459 0.233445 0.382683 0.522499 0.649448 0.760406 0.852640 0.923880 0.972370 0.996917 0.996917 0.972370 0.923880 0.852640 0.760406 0.649448 0.522499 0.382683 0.233445 0.078459]
+}

dsp/window/window_test.go

@@ -150,10 +150,18 @@ func TestWindows(t *testing.T) {
 			}
 
 			dst := test.fn(src)
-
 			if !floats.EqualApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for window function %q:\ngot:%#.6v\nwant:%#v", test.name, dst, test.want)
 			}
+
+			for i := range src {
+				src[i] = 1
+			}
+
+			dst = NewValues(test.fn, len(src)).Transform(src)
+			if !floats.EqualApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
 		})
 	}
 }
@@ -161,20 +169,29 @@ func TestWindows(t *testing.T) {
 func TestGausWindows(t *testing.T) {
 	const tol = 1e-6
 
-	src := make([]float64, 20)
-	for i := range src {
-		src[i] = 1
-	}
-
 	for _, test := range gausWindowTests {
 		t.Run(fmt.Sprintf("%s (sigma=%.1f)", test.name, test.sigma), func(t *testing.T) {
-			srcCpy := make([]float64, len(src))
+			src := make([]float64, 20)
-			copy(srcCpy, src)
+			for i := range src {
-			dst := Gaussian(srcCpy, test.sigma)
+				src[i] = 1
+			}
 
+			dst := Gaussian(src, test.sigma)
 			if !floats.EqualApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for window function %q:\ngot:%#.6v\nwant:%#v", test.name, dst, test.want)
 			}
+
+			for i := range src {
+				src[i] = 1
+			}
+
+			sigma := test.sigma
+			dst = NewValues(func(seq []float64) []float64 {
+				return Gaussian(seq, sigma)
+			}, len(src)).Transform(src)
+			if !floats.EqualApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
 		})
 	}
 }
@@ -190,10 +207,18 @@ func TestWindowsComplex(t *testing.T) {
 			}
 
 			dst := test.fnCmplx(src)
-
 			if !equalApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
 			}
+
+			for i := range src {
+				src[i] = complex(1, 1)
+			}
+
+			dst = NewValuesComplex(test.fnCmplx, len(src)).Transform(src)
+			if !equalApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
 		})
 	}
 }
@@ -201,20 +226,29 @@ func TestWindowsComplex(t *testing.T) {
 func TestGausWindowComplex(t *testing.T) {
 	const tol = 1e-6
 
-	src := make([]complex128, 20)
-	for i := range src {
-		src[i] = complex(1, 1)
-	}
-
 	for _, test := range gausWindowTests {
 		t.Run(fmt.Sprintf("%sComplex (sigma=%.1f)", test.name, test.sigma), func(t *testing.T) {
-			srcCpy := make([]complex128, len(src))
+			src := make([]complex128, 20)
-			copy(srcCpy, src)
+			for i := range src {
-			dst := GaussianComplex(srcCpy, test.sigma)
+				src[i] = complex(1, 1)
+			}
 
+			dst := GaussianComplex(src, test.sigma)
 			if !equalApprox(dst, test.want, tol) {
 				t.Errorf("unexpected result for window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
 			}
+
+			for i := range src {
+				src[i] = complex(1, 1)
+			}
+
+			sigma := test.sigma
+			dst = NewValuesComplex(func(seq []complex128) []complex128 {
+				return GaussianComplex(seq, sigma)
+			}, len(src)).Transform(src)
+			if !equalApprox(dst, test.want, tol) {
+				t.Errorf("unexpected result for lookup window function %q:\ngot:%#.6v\nwant:%#.6v", test.name, dst, test.want)
+			}
 		})
 	}
 }