Comment/cleanup of motion code

Marlin/src/module/motion.cpp

@@ -587,12 +587,9 @@ float soft_endstop_min[XYZ] = { X_MIN_BED, Y_MIN_BED, Z_MIN_POS },
     float raw[XYZE];
     COPY(raw, current_position);
 
-    // Drop one segment so the last move is to the exact target.
-    // If there's only 1 segment, loops will be skipped entirely.
-    --segments;
 
     // Calculate and execute the segments
-    for (uint16_t s = segments + 1; --s;) {
+    while (--segments) {
 
       static millis_t next_idle_ms = millis() + 200UL;
       thermalManager.manage_heater();  // This returns immediately if not really needed.
@@ -691,16 +688,12 @@ float soft_endstop_min[XYZ] = { X_MIN_BED, Y_MIN_BED, Z_MIN_POS },
       // SERIAL_ECHOPAIR("mm=", cartesian_mm);
       // SERIAL_ECHOLNPAIR(" segments=", segments);
 
-      // Drop one segment so the last move is to the exact target.
-      // If there's only 1 segment, loops will be skipped entirely.
-      --segments;
-
       // Get the raw current position as starting point
       float raw[XYZE];
       COPY(raw, current_position);
 
       // Calculate and execute the segments
-      for (uint16_t s = segments + 1; --s;) {
+      while (--segments) {
         static millis_t next_idle_ms = millis() + 200UL;
         thermalManager.manage_heater();  // This returns immediately if not really needed.
         if (ELAPSED(millis(), next_idle_ms)) {

Marlin/src/module/planner.h

@@ -505,8 +505,8 @@ class Planner {
     /**
      * Get the index of the next / previous block in the ring buffer
      */
-    static int8_t next_block_index(int8_t block_index) { return BLOCK_MOD(block_index + 1); }
-    static int8_t prev_block_index(int8_t block_index) { return BLOCK_MOD(block_index - 1); }
+    static int8_t next_block_index(const int8_t block_index) { return BLOCK_MOD(block_index + 1); }
+    static int8_t prev_block_index(const int8_t block_index) { return BLOCK_MOD(block_index - 1); }
 
     /**
      * Calculate the distance (not time) it takes to accelerate

Marlin/src/module/stepper.cpp

@@ -409,8 +409,7 @@ void Stepper::isr() {
   // If there is no current block, attempt to pop one from the buffer
   if (!current_block) {
     // Anything in the buffer?
-    current_block = planner.get_current_block();
-    if (current_block) {
+    if ((current_block = planner.get_current_block())) {
       trapezoid_generator_reset();
 
       // Initialize Bresenham counters to 1/2 the ceiling