better transposition algorithm

lina.c

@@ -12,25 +12,26 @@ void lina_dot(double *A, double *B, double *C, int m, int n, int l){
     assert(A != NULL && B != NULL && C != NULL);
     assert(A != C && B != C);
 
-    //Actual dot
-    //Iteration over A's rows
-    for(int i=0; i < m;i++){
+    // Iteration over A's rows
+    for(int i = 0; i < m; i++)
+        {
+            // Iteration over B's columns
+            for(int k = 0; k < l; k++)
+                {
+                    double pos = 0;
 
-        //Iteration over B's columns
-        for(int k=0; k < l; k++){
+                    // Iteration over the single B column 
+                    // for executing the product of sum
+                    
+                    for(int j=0; j < n; j++)
 
-            double pos = 0;
-
-            //Iteration over the single B column for executing the product of sum
-            for(int j=0; j < n; j++)
-                pos += A[i * n + j] * B[j * l + k];
-
-            //The usage of a support variable 'pos' is for safety purpose (non-zero C matrix)
-            C[i*l+k] = pos;
+                        pos += A[i*n + j] * B[j*l + k];
 
+                    // The usage of a support variable 'pos'
+                    // is for safety purpose (non-zero C matrix)
+                    C[i*l + k] = pos;
+                }
         }
-        
-    }
 
 }
 
@@ -40,10 +41,9 @@ void lina_add(double *A, double *B, double *C, int m, int n){
     assert(A != NULL && B != NULL && C != NULL);
     
     for(int i = 0; i < m; i++)
-
         for(int j = 0; j < n; j++)
 
-            C[i * n + j] = A[i * n + j] + B[i * n + j];
+            C[i*n + j] = A[i*n + j] + B[i*n + j];
 }
 
 void lina_scale(double *A, double *B, double k, int m, int n){
@@ -55,27 +55,46 @@ void lina_scale(double *A, double *B, double k, int m, int n){
 
         for(int j = 0; j < n; j++)
 
-            B[i * n + j] = k * A[i * n + j];
+            B[i*n + j] = k * A[i*n + j];
 }
 
-void lina_transpose(double *A, double *B, int m, int n){
-
+void lina_transpose(double *A, double *B, int m, int n)
+{
     assert(m > 0 && n > 0);
     assert(A != NULL && B != NULL);
 
-#warning "Try to think better algorithm"
+    if(m == 1 || n == 1)
+        {
+            memcpy(B, A, sizeof(A[0]) * m * n);
+            return;
+        }
 
-    double *support = malloc(sizeof(*support) * m * n);
+    if(m == n)
+        {
+            for(int i = 0; i < n; i += 1)
+                for(int j = 0; j < i+1; j += 1)
+                    {
+                        double temp = A[i*n + j];
+                        B[i*n + j] = A[j*n + i];
+                        B[j*n + i] = temp;
+                    }
+        }
+    else
+        {
+            B[0] = A[0];
+            B[m*n-1] = A[m*n-1];
 
-    check(support != NULL);
+            double item = A[1];
+            int    next = m;
 
-    memcpy(support, A, sizeof(*support) * m * n);
+            while(next != 1)
+                {
+                    double temp = A[next];
+                    B[next] = item;
+                    item = temp;
+                    next = (next % n) * m + (next / n);
+                }
 
-    for(int i = 0; i < n; i++)
-        
-        for(int j = 0; j < m; j++)
-
-            B[j*n + i] = support[i*m + j];
-
-    free(support);
+            B[1] = item;
+        }
 }