Move multiplications out of inner loop

1 files changed, 15 insertions, 10 deletions

diff --git a/dda.c b/dda.c
index 677638f..e6fe822 100644
--- a/dda.c
+++ b/dda.c
@@ -87,6 +87,13 @@ dda (test_data_t *testdata)
     int yi = next_sample_y (y0);
     int xi = next_sample_x (x0);
     double e = (sample_to_pos (xi) - x0) * dy - (sample_to_pos (yi) - y0) * dx;
+    double delta_e_big_x, delta_e_big_y;
+    double delta_e_small_x, delta_e_small_y;
+
+    delta_e_big_x = BIG_STEP_X * dy;
+    delta_e_small_x = SMALL_STEP_X * dy;
+    delta_e_big_y = BIG_STEP_Y * dx;
+    delta_e_small_y = SMALL_STEP_Y * dx;
 
     while (yi < next_sample_y (y1))
     {
@@ -96,13 +103,13 @@ dda (test_data_t *testdata)
 	    {
 		if ((xi & 0xff) == N_GRID_X - 1)
 		{
-		    e += BIG_STEP_X * dy;
+		    e += delta_e_big_x;
 		    xi += (1 << 8);
 		    xi &= 0xffffff00;
 		}
 		else
 		{
-		    e += SMALL_STEP_X * dy;
+		    e += delta_e_small_x;
 		    xi++;
 		}
 	    }
@@ -112,9 +119,9 @@ dda (test_data_t *testdata)
 	begin:
 	    if ((xi & 0xff) == 0)
 	    {
-		if (e > BIG_STEP_X * dy)
+		if (e > delta_e_big_x)
 		{
-		    e -= BIG_STEP_X * dy;
+		    e -= delta_e_big_x;
 		    xi -= (1 << 8);
 		    xi |= (N_GRID_X - 1);
 		    goto small;
@@ -123,9 +130,9 @@ dda (test_data_t *testdata)
 	    else
 	    {
 	    small:
-		if (e > SMALL_STEP_X * dy)
+		if (e > delta_e_small_x)
 		{
-		    e -= SMALL_STEP_X * dy;
+		    e -= delta_e_small_x;
 		    xi--;
 		    goto begin;
 		}
@@ -142,15 +149,13 @@ dda (test_data_t *testdata)
 
 	if ((yi & 0xff) == (N_GRID_Y - 1))
 	{
-	    e -= BIG_STEP_Y * dx;
-
+	    e -= delta_e_big_y;
 	    yi += (1 << 8);
 	    yi &= 0xffffff00;
 	}
 	else
 	{
-	    e -= SMALL_STEP_Y * dx;
-
+	    e -= delta_e_small_y;
 	    yi++;
 	}
     }