Merge correlation function into process, also add documentation

1 files changed, 28 insertions, 37 deletions

diff --git a/timestretch.c b/timestretch.c
index 1f94837..b9ae038 100644
--- a/timestretch.c
+++ b/timestretch.c
@@ -11,11 +11,11 @@ static short * g_overlap_buffer;
 static short * g_overlap_heuristic;
 static size_t  g_overlap;
 
-static size_t  g_input_length;  // Minimal length 
-static size_t  g_output_length;
-static size_t  g_corr_length;
+static size_t  g_skip;          // Per frame skip << 16, i.e. amount of samples consumed if not FRAME_LAST
+static size_t  g_input_length;  // Minimal length, not everything is used
+static size_t  g_output_length; // Exact length of output
+static size_t  g_corr_length;   // Length of frame part correlation is attempted in
 
-static size_t  g_skip;          // Per frame skip
 static size_t  g_offset;        // Offset into stream, lower bits
 
 #define FRAME_FIRST 0x01
@@ -29,7 +29,7 @@ static size_t  g_offset;        // Offset into stream, lower bits
 #define sampcpy(A,B,C) memcpy((A),(B),(C)*sizeof(short))
 
 // Returns the length of one output frame
-static size_t calc_convert_values( int sample_rate, float tempo ) {
+static size_t calc_convert_values( int sample_rate, double tempo ) {
     unsigned int i;
     g_overlap = ( sample_rate * OVERLAP ) / 1000;
 
@@ -48,9 +48,9 @@ static size_t calc_convert_values( int sample_rate, float tempo ) {
     // boost middle of sequence by top of a flat parabola
     // slope stolen from soundtouch, precalc table
     for( i = 0; i < g_corr_length; ++i )
-        g_overlap_heuristic[i] = (short)16384.0*(-(double)(i*i)/((double)(g_corr_length*g_corr_length))+(double)i/(double)g_corr_length+0.75f);
+        g_overlap_heuristic[i] = (short)16384.0*(-(double)(i*i)/((double)(g_corr_length*g_corr_length))+(double)i/(double)g_corr_length+0.75);
 
-    g_skip = (size_t)( tempo * (float)g_output_length * 65536.0 );
+    g_skip = (size_t)( tempo * (double)g_output_length * 65536.0 );
     g_input_length = g_corr_length + g_output_length + g_overlap;
     if( g_skip / 65536 > g_input_length )
         g_input_length = g_skip / 65536;
@@ -58,8 +58,7 @@ static size_t calc_convert_values( int sample_rate, float tempo ) {
     return g_output_length;
 }
 
-/*
-  Example: tempo 1.5 with 30/15/10 => skip == 45, out = 30
+/* Example: tempo 1.5 with 30/15/10 => skip == 45, out = 30
 we found an offset of 5 msec
 
   [#####OOOOOOOOOOVVVVVVVVVVVVVVVVVVVVmmmmmmmmmm?????????????????????????]
@@ -68,41 +67,33 @@ we found an offset of 5 msec
   [                                            #####OOOOOOOOOOVVVVVVVVVVVVVVVVVVVVmmmmmmmmmm?????????????????????????]
 */
 
-static unsigned int find_corr_max(const short *input, const short *mixbuf) {
-    unsigned int i, j, offs = 0;
-    int64_t acc, corr_max = 0;
-
-    // Scans for the best correlation value by testing each possible position
-    for (i = 0; i < g_corr_length; ++i) {
-        for(j = 0, acc = 0; j < g_overlap; ++j )
-            acc += input[i+j] * mixbuf[j];
-
-        acc *= g_overlap_heuristic[i];
-        if ( corr_max < acc ) {
-            offs = i;
-            corr_max = acc;
-        }
-    }
-
-//printf( "%03d %016llX\n", offs, corr_max );
-    return offs;
-}
-
 // Returns the amount of samples that can be discarded from begin of the input buffer
 size_t process_frame( short *input, short *output, short *overlap, int frame_flag ) {
-    int i, i_ = (int)g_overlap;
-    unsigned int offset = 0;
+    int offset = 0;
 
-    // The first frame needs to be copied verbatim,
-    // we do not have anything to mix, yet.
+    // The first frame needs to be copied verbatim, we do not have anything to mix, yet.
     if( frame_flag & FRAME_FIRST )
         sampcpy( output, input, g_output_length );
     else {
-        offset = find_corr_max( input, overlap );
+        int64_t acc, corr_max = 0;
+        int i, j;
+
+        // Scans for the best correlation value by testing each possible position
+        for( i = 0; i < (int)g_corr_length; ++i ) {
+            for( j = 0, acc = 0; j < (int)g_overlap; ++j )
+                acc += input[i+j] * overlap[j];
+
+            acc *= g_overlap_heuristic[i];
+            if ( corr_max < acc ) {
+                offset = i;
+                corr_max = acc;
+            }
+        }
+//printf( "%03d %016llX\n", offset, corr_max );
 
         // Cross fade end of last frame with begin of this frame
-        for (i = 0; i < (int)g_overlap ; ++i, --i_ )
-            output[i] = ( i_ * overlap[i] + i * input[i+offset] ) / (int)g_overlap;
+        for( i = 0, j = (int)g_overlap; i < (int)g_overlap ; ++i, --j )
+            output[i] = ( j * overlap[i] + i * input[i+offset] ) / (int)g_overlap;
 
         // Copy rest of the input verbatim
         sampcpy( output + g_overlap, input + offset + g_overlap, g_output_length - g_overlap );
@@ -122,7 +113,7 @@ size_t process_frame( short *input, short *output, short *overlap, int frame_fla
 }
 
 int main( int args, char **argv ) {
-  size_t    out_chunk_size = calc_convert_values( 8000, 1.25f );
+  size_t    out_chunk_size = calc_convert_values( 8000, 1.25 );
   size_t    in_fill = 0;
   short     outbuf[ g_output_length ];
   short     inbuf [ g_input_length  ];