# HG changeset patch
# User Chris Cannam
# Date 1615453093 0
#      Thu Mar 11 08:58:13 2021 +0000
# Node ID c6fe20667eda14ea1b64718afebe857e3c5f7fc6
# Parent  2da672dd06e362d76ad939d2e9f555b524e6d585
Further simplification of tables

diff --git a/src/FFT.cpp b/src/FFT.cpp
--- a/src/FFT.cpp
+++ b/src/FFT.cpp
@@ -1657,10 +1657,8 @@
         m_b = allocate_and_zero<double>(m_half + 1);
         m_c = allocate_and_zero<double>(m_half + 1);
         m_d = allocate_and_zero<double>(m_half + 1);
-        m_cos_f = allocate_and_zero<double>(m_half / 2);
-        m_sin_f = allocate_and_zero<double>(m_half / 2);
-        m_cos_i = allocate_and_zero<double>(m_half / 2);
-        m_sin_i = allocate_and_zero<double>(m_half / 2);
+        m_cos = allocate_and_zero<double>(m_half / 2);
+        m_sin = allocate_and_zero<double>(m_half / 2);
         m_vr = allocate_and_zero<double>(m_half);
         m_vi = allocate_and_zero<double>(m_half);
         makeTables();
@@ -1672,10 +1670,8 @@
         deallocate(m_b);
         deallocate(m_c);
         deallocate(m_d);
-        deallocate(m_cos_f);
-        deallocate(m_sin_f);
-        deallocate(m_cos_i);
-        deallocate(m_sin_i);
+        deallocate(m_cos);
+        deallocate(m_sin);
         deallocate(m_vr);
         deallocate(m_vi);
     }
@@ -1822,10 +1818,8 @@
     double *m_b;
     double *m_c;
     double *m_d;
-    double *m_cos_f;
-    double *m_sin_f;
-    double *m_cos_i;
-    double *m_sin_i;
+    double *m_cos;
+    double *m_sin;
     double *m_vr;
     double *m_vi;
 
@@ -1858,10 +1852,8 @@
         // additional factors for real-complex transform
         for (i = 0; i < n/2; ++i) {
             double phase = M_PI * (double(i + 1) / double(m_half) + 0.5);
-            m_cos_f[i] = cos(phase);
-            m_sin_f[i] = sin(phase);
-            m_cos_i[i] = cos(-phase);
-            m_sin_i[i] = sin(-phase);
+            m_cos[i] = cos(phase);
+            m_sin[i] = sin(phase);
         }
     }        
 
@@ -1880,8 +1872,8 @@
         ro[m_half] = m_vr[0] - m_vi[0];
         io[0] = io[m_half] = 0.0;
         for (int i = 0; i < halfhalf; ++i) {
-            double c = m_cos_f[i];
-            double s = -m_sin_f[i];
+            double c = m_cos[i];
+            double s = -m_sin[i];
             int k = i + 1;
             double r0 = m_vr[k];
             double i0 = m_vi[k];
@@ -1905,8 +1897,8 @@
         m_vr[0] = ri[0] + ri[m_half];
         m_vi[0] = ri[0] - ri[m_half];
         for (int i = 0; i < halfhalf; ++i) {
-            double c = m_cos_f[i];
-            double s = m_sin_f[i];
+            double c = m_cos[i];
+            double s = m_sin[i];
             int k = i + 1;
             double r0 = ri[k];
             double r1 = ri[m_half - k];
diff --git a/test/TestFFT.cpp b/test/TestFFT.cpp
--- a/test/TestFFT.cpp
+++ b/test/TestFFT.cpp
@@ -175,6 +175,28 @@
     COMPARE_SCALED(back, in, 4);
 }
 
+ALL_IMPL_AUTO_TEST_CASE(sine_8)
+{
+    // Longer sine. With only 4 elements, the real transform only
+    // needs to get the DC and Nyquist bins right for its two complex
+    // sub-transforms. We need a longer test to check the real
+    // transform is working properly.
+    double cospi4 = 0.5 * sqrt(2.0);
+    double in[] = { 0, cospi4, 1.0, cospi4, 0.0, -cospi4, -1.0, -cospi4 };
+    double re[5], im[5];
+    USING_FFT(8);
+    fft.forward(in, re, im);
+    COMPARE_ALL(re, 0.0);
+    COMPARE_ZERO(im[0]);
+    COMPARE(im[1], -4.0);
+    COMPARE_ZERO(im[2]);
+    COMPARE_ZERO(im[3]);
+    COMPARE_ZERO(im[4]);
+    double back[8];
+    fft.inverse(re, im, back);
+    COMPARE_SCALED(back, in, 8);
+}
+
 ALL_IMPL_AUTO_TEST_CASE(cosine)
 {
     // Cosine. Output is purely real
@@ -190,6 +212,25 @@
     fft.inverse(re, im, back);
     COMPARE_SCALED(back, in, 4);
 }
+
+ALL_IMPL_AUTO_TEST_CASE(cosine_8)
+{
+    // Longer cosine.
+    double cospi4 = 0.5 * sqrt(2.0);
+    double in[] = { 1.0, cospi4, 0.0, -cospi4, -1.0, -cospi4, 0.0, cospi4 };
+    double re[5], im[5];
+    USING_FFT(8);
+    fft.forward(in, re, im);
+    COMPARE_ALL(im, 0.0);
+    COMPARE_ZERO(re[0]);
+    COMPARE(re[1], 4.0);
+    COMPARE_ZERO(re[2]);
+    COMPARE_ZERO(re[3]);
+    COMPARE_ZERO(re[4]);
+    double back[8];
+    fft.inverse(re, im, back);
+    COMPARE_SCALED(back, in, 8);
+}
 	
 ALL_IMPL_AUTO_TEST_CASE(sineCosine)
 {