dda.c: file attempt to use sign of dda->delta_um[] to set direction.

attic/dda.c-attempts-to-use-sign-of-dda-delta_um-to-set-di.patch

@@ -0,0 +1,49 @@
+From c8e28f3ff9b72eace20cce851d77a6de5e995c69 Mon Sep 17 00:00:00 2001
+From: Markus Hitter <mah@jump-ing.de>
+Date: Sun, 12 Oct 2014 23:17:48 +0200
+Subject: [PATCH] dda.c: attempts to use sign of dda->delta_um[] to set
+ direction.
+
+At that point we stored movement distance in steps signed in
+dda->delta_um[] as well as unsigned in dda->delta[] plus its
+sign in dda->{xyze}_direction. That's obvously redundant, so
+the try was to get rid of the redundancy.
+
+However, dda_start() is the most time critical part when using
+look-ahead, so this attemt was dropped. Next attempt will be to
+use dda->{xyze}_direction in dda_find_crossing_speed(), the only
+usage of the dda->delta_um[].
+---
+ dda.c | 16 +++++++++++++++-
+ 1 file changed, 15 insertions(+), 1 deletion(-)
+
+diff --git a/dda.c b/dda.c
+index 8d53256..195e472 100644
+--- a/dda.c
++++ b/dda.c
+@@ -468,7 +468,21 @@ void dda_start(DDA *dda) {
+ 			endstops_on();
+ 
+ 		// set direction outputs
+-		x_direction(dda->x_direction);
++    // This is the fastest one.
++    x_direction(dda->x_direction); // 20164 bytes
++    // Costs 14 additional CPU clock cycles.
++    //x_direction(dda->delta_um[X] < 0 ? 1 : 0); // 20184 bytes
++    // Costs 12 additional CPU clock cycles.
++    //x_direction(dda->delta_um[X] >> (sizeof(int32_t) * 8 - 1)); // 20178 bytes
++    // Costs 14 additional CPU clock cycles.
++    //x_direction(dda->delta_um[X] > 0); // 20184 bytes
++    // Costs 12 additional CPU clock cycles.
++    //x_direction(dda->delta_um[X] < 0); // 20178 bytes
++    // Costs 5 additional CPU clock cycles.
++    //x_direction( ! ((*((uint8_t *)(&dda->delta_um[X]) + 3)) & 0x80)); // 20172 bytes
++    // Check just the last byte, that's smaller and faster.
++    // Costs 6 additional CPU clock cycles.
++    //x_direction((*((uint8_t *)(&dda->delta_um[X]) + 3)) > 0); // 20172 bytes
+ 		y_direction(dda->y_direction);
+ 		z_direction(dda->z_direction);
+ 		e_direction(dda->e_direction);
+-- 
+2.1.0
+