diff --git a/gpu/tp5/c/build.sh b/gpu/tp5/c/build.sh
index 22ebca9..1c788f8 100755
--- a/gpu/tp5/c/build.sh
+++ b/gpu/tp5/c/build.sh
@@ -13,7 +13,7 @@ fi
 
 mkdir -p bin
 
-cc=hipcc
+cc=nvcc
 ccargs="-O2"
 #ccargs="$ccargs -g -G -Xcompiler -fsanitize=address"
 
diff --git a/gpu/tp5/c/src/matrix.cu b/gpu/tp5/c/src/matrix.cu
index 5e5a350..9b8b3f0 100644
--- a/gpu/tp5/c/src/matrix.cu
+++ b/gpu/tp5/c/src/matrix.cu
@@ -22,10 +22,10 @@ inline void cuda_check(cudaError_t code, const char* file, int line) {
 // step 01
 // return the 1D index of a row-major matrix of size (rows,cols) from 2D indices (i,j)
 //
-__host__ __device__ int index1(int i, int j, int rows, int cols) {
-	if (i < 0 || i >= rows) return -1;
-	if (j < 0 || j >= cols) return -1;
-	return (i * cols) + j;
+__host__ __device__ int index1(int y, int x, int height, int width) {
+	if (y < 0 || y >= height) return -1;
+	if (x < 0 || x >= width) return -1;
+	return (y * width) + x;
 }
 
 template <typename T>
@@ -189,6 +189,8 @@ __global__ void matmul3(const int* A, const int* B, int* C, int N, int M, int P)
 
 	auto result_height = A_height;
 	auto result_width = B_width;
+	auto index = index1(THREAD_GID(y), THREAD_GID(x), result_height, result_width);
+	if (index == -1) return;
 
 	auto result = 0;
 	auto thread_x = threadIdx.x;
@@ -199,8 +201,7 @@ __global__ void matmul3(const int* A, const int* B, int* C, int N, int M, int P)
 		__shared__ int local_B[T][T];
 		auto index_A = index2(thread_y, thread_x, blockIdx.y, step_index, A_height, A_width);
 		auto index_B = index2(thread_y, thread_x, step_index, blockIdx.x, B_height, B_width);
-		if (index_A == -1) return;
-		if (index_B == -1) return;
+		if (index_A == -1 || index_B == -1) continue;
 		local_A[thread_x][thread_y] = A[index_A];
 		local_B[thread_x][thread_y] = B[index_B];
 		__syncthreads();
@@ -211,7 +212,6 @@ __global__ void matmul3(const int* A, const int* B, int* C, int N, int M, int P)
 		}
 		__syncthreads();
 	}
-	auto index = index1(THREAD_GID(y), THREAD_GID(x), result_height, result_width);
 	C[index] = result;
 }