Rewrite sym_defer_pr

* Modernise code using sym_defer_pk as template
* Format consistency with other current algorithms

quantum/debounce/sym_defer_pr.c

@@ -1,5 +1,7 @@
 /*
-Copyright 2021 Chad Austin <chad@chadaustin.me>
+Copyright 2017 Alex Ong<the.onga@gmail.com>
+Copyright 2020 Andrei Purdea<andrei@purdea.ro>
+Copyright 2021 Simon Arlott
 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation, either version 2 of the License, or
@@ -13,66 +15,122 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
 /*
-Symmetric per-row debounce algorithm. Changes only apply when
-DEBOUNCE milliseconds have elapsed since the last change.
+Basic symmetric per-row algorithm. Uses an 8-bit counter per row.
+When no state changes have occured for DEBOUNCE milliseconds, we push the state.
 */
 
 #include "debounce.h"
 #include "timer.h"
 #include "util.h"
-#include <string.h>
+
+#ifdef PROTOCOL_CHIBIOS
+#    if CH_CFG_USE_MEMCORE == FALSE
+#        error ChibiOS is configured without a memory allocator. Your keyboard may have set `#define CH_CFG_USE_MEMCORE FALSE`, which is incompatible with this debounce algorithm.
+#    endif
+#endif
 
 #ifndef DEBOUNCE
 #    define DEBOUNCE 5
 #endif
 
-static uint16_t last_time;
-// Countdown timers for each matrix row, indexed by row.
-static uint8_t countdowns[MATRIX_ROWS_PER_HAND] = {0};
-// Last raw state for each matrix row, indexed by row.
-static matrix_row_t last_raw[MATRIX_ROWS_PER_HAND] = {0};
+// Maximum debounce: 255ms
+#if DEBOUNCE > UINT8_MAX
+#    undef DEBOUNCE
+#    define DEBOUNCE UINT8_MAX
+#endif
 
-void debounce_init(uint8_t num_rows) {
-    memset(countdowns, 0, sizeof(countdowns));
-    memset(last_raw, 0, sizeof(last_raw));
-}
+typedef uint8_t debounce_counter_t;
+
+#if DEBOUNCE > 0
+// Uses MATRIX_ROWS_PER_HAND instead of MATRIX_ROWS to support split keyboards
+static debounce_counter_t debounce_counters[MATRIX_ROWS_PER_HAND] = {0};
+static fast_timer_t       last_time;
+static bool               counters_need_update;
+static bool               cooked_changed;
+
+#    define DEBOUNCE_ELAPSED 0
+
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t elapsed_time);
+static void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[]);
+
+void debounce_init(uint8_t num_rows) {}
 
-/**
- * @brief Debounces the raw matrix state and updates the cooked (debounced) state.
- *
- * For each row in the matrix, this function tracks changes and applies a debounce period.
- * If a row's state changes, its countdown timer is reset. If the countdown timer expires,
- * the debounced state is updated to match the raw state.
- *
- * @param raw The current raw key state matrix.
- * @param cooked The debounced key state matrix to be updated.
- * @param num_rows Number of rows in the matrix.
- * @param changed True if the raw matrix has changed since the last call.
- * @return true if the debounced matrix has new key changes, false otherwise.
- */
 bool debounce(matrix_row_t raw[], matrix_row_t cooked[], uint8_t num_rows, bool changed) {
-    uint16_t now           = timer_read();
-    uint16_t elapsed16     = TIMER_DIFF_16(now, last_time);
-    last_time              = now;
-    uint8_t elapsed        = MIN(elapsed16, UINT8_MAX);
-    bool    cooked_changed = false;
+    bool updated_last = false;
+    cooked_changed    = false;
 
-    uint8_t* countdown = countdowns;
+    if (counters_need_update) {
+        fast_timer_t now          = timer_read_fast();
+        fast_timer_t elapsed_time = TIMER_DIFF_FAST(now, last_time);
 
-    for (uint8_t row = 0; row < MATRIX_ROWS_PER_HAND; ++row, ++countdown) {
-        matrix_row_t raw_row = raw[row];
+        last_time    = now;
+        updated_last = true;
 
-        if (raw_row != last_raw[row]) {
-            *countdown    = DEBOUNCE;
-            last_raw[row] = raw_row;
-        } else if (*countdown > elapsed) {
-            *countdown -= elapsed;
-        } else if (*countdown) {
-            cooked_changed |= cooked[row] ^ raw_row;
-            cooked[row] = raw_row;
-            *countdown  = 0;
+        if (elapsed_time > 0) {
+            // Update debounce counters with elapsed timer clamped to UINT8_MAX
+            update_debounce_counters_and_transfer_if_expired(raw, cooked, MIN(elapsed_time, UINT8_MAX));
         }
     }
 
+    if (changed) {
+        if (!updated_last) {
+            last_time = timer_read_fast();
+        }
+
+        start_debounce_counters(raw, cooked);
+    }
+
     return cooked_changed;
 }
+
+/**
+ * @brief Updates debounce counters and transfers debounced row states if the debounce period has expired.
+ *
+ * Iterates through each row in the matrix and checks its debounce counter. If the debounce period has expired
+ * for a row, the debounced state is updated to match the raw state. Otherwise, the debounce counter is decremented
+ * by the elapsed time and marked for further updates.
+ *
+ * @param raw The current raw key state matrix.
+ * @param cooked The debounced key state matrix to be updated.
+ * @param elapsed_time The time elapsed since the last debounce update, in milliseconds.
+ */
+static void update_debounce_counters_and_transfer_if_expired(matrix_row_t raw[], matrix_row_t cooked[], uint8_t elapsed_time) {
+    counters_need_update = false;
+    for (uint8_t row = 0; row < MATRIX_ROWS_PER_HAND; row++) {
+        if (debounce_counters[row] != DEBOUNCE_ELAPSED) {
+            if (debounce_counters[row] <= elapsed_time) {
+                debounce_counters[row] = DEBOUNCE_ELAPSED;
+                cooked_changed |= cooked[row] ^ raw[row];
+                cooked[row] = raw[row];
+            } else {
+                debounce_counters[row] -= elapsed_time;
+                counters_need_update = true;
+            }
+        }
+    }
+}
+
+/**
+ * @brief Initializes debounce counters for rows with changed states.
+ *
+ * For each row in the matrix, this function checks if the raw state differs from the debounced state.
+ * If a change is detected and the debounce counter has elapsed, the counter is set to the debounce period
+ * and marked for update. Otherwise, the counter is cleared.
+ *
+ * @param raw The current raw key state matrix.
+ * @param cooked The debounced key state matrix.
+ */
+static void start_debounce_counters(matrix_row_t raw[], matrix_row_t cooked[]) {
+    for (uint8_t row = 0; row < MATRIX_ROWS_PER_HAND; row++) {
+        if (raw[row] != cooked[row]) {
+            debounce_counters[row] = DEBOUNCE;
+            counters_need_update   = true;
+        } else {
+            debounce_counters[row] = DEBOUNCE_ELAPSED;
+        }
+    }
+}
+
+#else
+#    include "none.c"
+#endif