quad: fix queue implementation so usage meets expectations

quad/src/queue/queue.c

 #include "queue.h"
 
-int queue_init(struct Queue *q, volatile unsigned char *buff, unsigned int max_size) {
+int queue_init(struct Queue *q, volatile unsigned char *buff, unsigned int max_size_plus1) {
   q->buff = buff;
-  q->max_size = max_size + 1;
-  q->start = max_size;
+  q->max_size_plus1 = max_size_plus1;
+  q->start = max_size_plus1 - 1;
   q->end = 0;
   return 0;
 }
@@ -13,7 +13,7 @@ struct Queue * queue_malloc(unsigned int max_size) {
   if (buff == NULL) return NULL;
   struct Queue *q = malloc(sizeof(struct Queue));
   if (q == NULL) return NULL;
-  queue_init(q, buff, max_size);
+  queue_init(q, buff, max_size + 1);
   return q;
 }
 
@@ -28,7 +28,7 @@ int queue_add(struct Queue *q, unsigned char c) {
   }
   q->buff[q->end] = c;
   q->end += 1;
-  q->end %= q->max_size;
+  q->end %= q->max_size_plus1;
   return 0;
 }
 
@@ -37,17 +37,17 @@ int queue_remove(struct Queue *q, unsigned char *c) {
     return -1;
   }
   q->start += 1;
-  q->start %= q->max_size;
+  q->start %= q->max_size_plus1;
   *c = q->buff[q->start];
   return 0;
 }
 
 int queue_size(struct Queue *q) {
-  return (q->max_size + q->end - q->start - 1) % q->max_size;
+  return (q->max_size_plus1 + q->end - q->start - 1) % q->max_size_plus1;
 }
 
 int queue_full(struct Queue *q) {
-  return q->start == q->end;;
+  return q->start == q->end;
 }
 
 int queue_empty(struct Queue *q) {
@@ -57,7 +57,7 @@ int queue_empty(struct Queue *q) {
 void queue_print(struct Queue *q) {
   int i;
   printf("buffer: (size: %d, full: %d, empty: %d)\n", queue_size(q), queue_full(q), queue_empty(q));
-  for (i = 0; i < q->max_size; i += 1) {
+  for (i = 0; i < q->max_size_plus1; i += 1) {
     char c = (char) q->buff[i];
     if (c == 0) c = '-';
     printf("%c", c);;

quad/src/queue/queue.h

@@ -6,13 +6,13 @@
 
 struct Queue {
   volatile unsigned char *buff;
-  unsigned int max_size;
+  unsigned int max_size_plus1;
   unsigned int start;
   unsigned int end;
 };
 
 
-int queue_init(struct Queue *q, volatile unsigned char *buff, unsigned int max_size);
+int queue_init(struct Queue *q, volatile unsigned char *buff, unsigned int max_size_plus1);
 struct Queue * queue_malloc(unsigned int max_size);
 void queue_free(struct Queue *q);
 int queue_add(struct Queue *q, unsigned char c);