1 files changed, 24 insertions, 0 deletions
diff --git a/externals/grill/fftease/src/fold.c b/externals/grill/fftease/src/fold.c
new file mode 100644
index 00000000..0ecee5d6
--- /dev/null
+++ b/externals/grill/fftease/src/fold.c
@@ -0,0 +1,24 @@
+/*
+ * multiply current input I by window W (both of length Nw);
+ * using modulus arithmetic, fold and rotate windowed input
+ * into output array O of (FFT) length N according to current
+ * input time n
+ */
+void fold( float *I, float  *W, int Nw, float *O, int N, int n )
+{
+ 
+    int i;
+
+    for ( i = 0; i < N; i++ )
+	O[i] = 0.;
+
+    while ( n < 0 )
+	n += N;
+    n %= N;
+    for ( i = 0; i < Nw; i++ ) {
+	O[n] += I[i]*W[i];
+	if ( ++n == N )
+	    n = 0;
+    }
+}
+