From d705a5b45efa4c7a47650fc2c187ff1d025db8fa Mon Sep 17 00:00:00 2001
From: Scott Lahteine <github@thinkyhead.com>
Date: Tue, 13 Apr 2021 23:22:57 -0500
Subject: [PATCH] Fix long acceleration overflow

---
 Marlin/src/module/planner.cpp | 23 +++++++++++------------
 Marlin/src/module/planner.h   |  2 +-
 2 files changed, 12 insertions(+), 13 deletions(-)

diff --git a/Marlin/src/module/planner.cpp b/Marlin/src/module/planner.cpp
index d6356432e7..b528eb9d3b 100644
--- a/Marlin/src/module/planner.cpp
+++ b/Marlin/src/module/planner.cpp
@@ -207,7 +207,7 @@ skew_factor_t Planner::skew_factor; // Initialized by settings.load()
 
 xyze_long_t Planner::position{0};
 
-uint32_t Planner::cutoff_long;
+uint32_t Planner::acceleration_long_cutoff;
 
 xyze_float_t Planner::previous_speed;
 float Planner::previous_nominal_speed_sqr;
@@ -2271,23 +2271,22 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
   // Compute and limit the acceleration rate for the trapezoid generator.
   const float steps_per_mm = block->step_event_count * inverse_millimeters;
   uint32_t accel;
-  if (!block->steps.a && !block->steps.b && !block->steps.c) {
-    // convert to: acceleration steps/sec^2
-    accel = CEIL(settings.retract_acceleration * steps_per_mm);
-    TERN_(LIN_ADVANCE, block->use_advance_lead = false);
+  if (!block->steps.a && !block->steps.b && !block->steps.c) {    // Is this a retract / recover move?
+    accel = CEIL(settings.retract_acceleration * steps_per_mm);   // Convert to: acceleration steps/sec^2
+    TERN_(LIN_ADVANCE, block->use_advance_lead = false);          // No linear advance for simple retract/recover
   }
   else {
     #define LIMIT_ACCEL_LONG(AXIS,INDX) do{ \
       if (block->steps[AXIS] && max_acceleration_steps_per_s2[AXIS+INDX] < accel) { \
-        const uint32_t comp = max_acceleration_steps_per_s2[AXIS+INDX] * block->step_event_count; \
-        if (accel * block->steps[AXIS] > comp) accel = comp / block->steps[AXIS]; \
+        const uint32_t max_possible = max_acceleration_steps_per_s2[AXIS+INDX] * block->step_event_count / block->steps[AXIS]; \
+        NOMORE(accel, max_possible); \
       } \
     }while(0)
 
     #define LIMIT_ACCEL_FLOAT(AXIS,INDX) do{ \
       if (block->steps[AXIS] && max_acceleration_steps_per_s2[AXIS+INDX] < accel) { \
-        const float comp = (float)max_acceleration_steps_per_s2[AXIS+INDX] * (float)block->step_event_count; \
-        if ((float)accel * (float)block->steps[AXIS] > comp) accel = comp / (float)block->steps[AXIS]; \
+        const float max_possible = float(max_acceleration_steps_per_s2[AXIS+INDX]) * float(block->step_event_count) / float(block->steps[AXIS]); \
+        NOMORE(accel, max_possible); \
       } \
     }while(0)
 
@@ -2336,7 +2335,7 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
     #endif
 
     // Limit acceleration per axis
-    if (block->step_event_count <= cutoff_long) {
+    if (block->step_event_count <= acceleration_long_cutoff) {
       LIMIT_ACCEL_LONG(A_AXIS, 0);
       LIMIT_ACCEL_LONG(B_AXIS, 0);
       LIMIT_ACCEL_LONG(C_AXIS, 0);
@@ -2352,7 +2351,7 @@ bool Planner::_populate_block(block_t * const block, bool split_move,
   block->acceleration_steps_per_s2 = accel;
   block->acceleration = accel / steps_per_mm;
   #if DISABLED(S_CURVE_ACCELERATION)
-    block->acceleration_rate = (uint32_t)(accel * (4096.0f * 4096.0f / (STEPPER_TIMER_RATE)));
+    block->acceleration_rate = (uint32_t)(accel * (sq(4096.0f) / (STEPPER_TIMER_RATE)));
   #endif
   #if ENABLED(LIN_ADVANCE)
     if (block->use_advance_lead) {
@@ -3020,7 +3019,7 @@ void Planner::reset_acceleration_rates() {
     max_acceleration_steps_per_s2[i] = settings.max_acceleration_mm_per_s2[i] * settings.axis_steps_per_mm[i];
     if (AXIS_CONDITION) NOLESS(highest_rate, max_acceleration_steps_per_s2[i]);
   }
-  cutoff_long = 4294967295UL / highest_rate; // 0xFFFFFFFFUL
+  acceleration_long_cutoff = 4294967295UL / highest_rate; // 0xFFFFFFFFUL
   TERN_(HAS_LINEAR_E_JERK, recalculate_max_e_jerk());
 }
 
diff --git a/Marlin/src/module/planner.h b/Marlin/src/module/planner.h
index d4ed00d2fa..398339f04e 100644
--- a/Marlin/src/module/planner.h
+++ b/Marlin/src/module/planner.h
@@ -443,7 +443,7 @@ class Planner {
     /**
      * Limit where 64bit math is necessary for acceleration calculation
      */
-    static uint32_t cutoff_long;
+    static uint32_t acceleration_long_cutoff;
 
     #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
       static float last_fade_z;