From 4e4884d602887c5d8f886bf51188c645a8e7d310 Mon Sep 17 00:00:00 2001
From: Tim Redfern <tim@getdrop.com>
Date: Tue, 15 Nov 2022 23:44:36 +0000
Subject: offset read by 1

---
 audioin/src/ofApp.h | 54 +++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 50 insertions(+), 4 deletions(-)

(limited to 'audioin')

diff --git a/audioin/src/ofApp.h b/audioin/src/ofApp.h
index d62dfa0..3ac6b39 100644
--- a/audioin/src/ofApp.h
+++ b/audioin/src/ofApp.h
@@ -23,16 +23,62 @@ public:
             //delete[] data; //why is this throwing an error
         }
     }
+/*
+if the size is 1000 and the num is 600
+1st frame: writePoint=0
+memcpy(&data[0],input,min(600,1000-0))
+-> we copied the whole 600 starting at 0 and ending at 599
+2nd frame: writePoint=600
+memcpy(&data[600],input, min(600,1000-600))
+-> we copied 400 starting at 600 and ending at 999
+yes (1000-600<600)
+    so 
+    memcpy(data,&input[1000-600],600-(1000-600))
+    -> we copied 200 starting at input:400 and ending at 599 to the start of data
+    writePoint=600-(1000-600)
+3rd frame: writePoint=200
+memcpy(&data[200],input, min(600,1000-200))
+-> we copied the whole 600 starting at 200 and ending at 799
+4th frame: writePoint=800
+memcpy(&data[800],input, min(600,1000-800))
+-> we copied 200 starting at 800 and ending at 999
+yes (1000-800<600)
+    so 
+    memcpy(data,&input[1000-800],600-(1000-800))
+    -> we copied 400 starting at input:200 and ending at 599 to the start of data
+    writePoint=600-(1000-800)
+5th frame: writePoint=400
+memcpy(&data[400],input, min(600,1000-400))
+-> we copied the whole 600 starting at 400 and ending at 999
+
+back to square one. 5*600=3000
+*/    
     void add(float * input, int num){
         memcpy(&data[writePoint],input,min(num,size-writePoint)*sizeof(float));
-        if (size-writePoint<num){
-            memcpy(data,&input[(size-writePoint)],(num-(size-writePoint))*sizeof(float));
+        if (size-writePoint<num){ //we have to wrap
+            //copy the remaining chunk to the start
+            memcpy(data,&input[size-writePoint],(num-(size-writePoint))*sizeof(float));
             writePoint=num-(size-writePoint);
         }
         else writePoint+=num;
     }
-    float operator [] (int i) const {return data[writePoint>i?writePoint-i:size-(i-writePoint)];}
-    float& operator [] (int i) {return data[writePoint>i?writePoint-i:size-(i-writePoint)];}
+/*
+if size is 1000 and writePoint is 1000
+0: return data[1000]
+writePoint can never be 1000?
+
+if size is 1000 and writePoint is 800
+0: return data[800]
+1: return data[799]
+799: return data[1] --> this should be data[0] !?
+800: return data[1000-(800-800)->1000] -> this should be data[999]
+*/
+    float operator [] (int i) const {
+        return data[(writePoint>i?writePoint-i:size-(i-writePoint))-1];
+    }
+    float& operator [] (int i) {
+        return data[(writePoint>i?writePoint-i:size-(i-writePoint))-1];
+    }
 private:
     size_t size;
     float *data;
-- 
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