cgraph agxbuf: abstract calculation of the capacity of a backing store

This looks a bit like overkill. However, an upcoming commit will make how we
determine this capacity conditional.

Gitlab: #2302

diff --git a/lib/cgraph/agxbuf.h b/lib/cgraph/agxbuf.h
index fa1d2b6a97b691ae392acf187043d922b66b5d36..6ff51f5da75117afa16829d4dee2dcf6248d5f07 100644 (file)
--- a/lib/cgraph/agxbuf.h
+++ b/lib/cgraph/agxbuf.h
@@ -64,6 +64,15 @@ static inline void agxbfree(agxbuf *xb) {
  */
 static inline size_t agxblen(const agxbuf *xb) { return xb->size; }
 
+/// get the capacity of the backing memory of a buffer
+///
+/// In contrast to \p agxblen, this is the total number of usable bytes in the
+/// backing store, not the total number of currently stored bytes.
+///
+/// \param xb Buffer to operate on
+/// \return Number of usable bytes in the backing store
+static inline size_t agxbsizeof(const agxbuf *xb) { return xb->capacity; }
+
 /* agxbpop:
  * Removes last character added, if any.
  */
@@ -87,7 +96,7 @@ static inline void agxbmore(agxbuf *xb, size_t ssz) {
   size_t nsize = 0; // new buffer size
   char *nbuf;       // new buffer
 
-  size = xb->capacity;
+  size = agxbsizeof(xb);
   nsize = size == 0 ? BUFSIZ : (2 * size);
   if (size + ssz > nsize)
     nsize = size + ssz;
@@ -137,7 +146,7 @@ static inline PRINTF_LIKE(2, 3) int agxbprint(agxbuf *xb, const char *fmt,
 
   // do we need to expand the buffer?
   {
-    size_t unused_space = xb->capacity - xb->size;
+    size_t unused_space = agxbsizeof(xb) - agxblen(xb);
     if (unused_space < size) {
       size_t extra = size - unused_space;
       agxbmore(xb, extra);
@@ -164,7 +173,7 @@ static inline size_t agxbput_n(agxbuf *xb, const char *s, size_t ssz) {
   if (ssz == 0) {
     return 0;
   }
-  if (ssz > xb->capacity - xb->size)
+  if (ssz > agxbsizeof(xb) - agxblen(xb))
     agxbmore(xb, ssz);
   memcpy(&xb->buf[xb->size], s, ssz);
   xb->size += ssz;
@@ -185,7 +194,7 @@ static inline size_t agxbput(agxbuf *xb, const char *s) {
  *  int agxbputc(agxbuf*, char)
  */
 static inline int agxbputc(agxbuf *xb, char c) {
-  if (xb->size >= xb->capacity) {
+  if (agxblen(xb) >= agxbsizeof(xb)) {
     agxbmore(xb, 1);
   }
   xb->buf[xb->size] = c;