MINOR: buffers: simplify b_contig_space()

This function is used a lot in block copies and is needlessly
complicated since it still uses pointer arithmetic. Let's fall
back to regular offsets and simplify it. This removed around
23 bytes from b_putblk() and it removed any conditional jump.

diff --git a/include/common/buf.h b/include/common/buf.h
index 92db0a174bc213312bf0fe556e5c00658de41b1a..4ccc8b0ed63d1f5dcb073bb1f6b82cf2d7b74675 100644 (file)
--- a/include/common/buf.h
+++ b/include/common/buf.h
@@ -300,21 +300,28 @@ static inline size_t b_contig_data(const struct buffer *b, size_t start)
 }
 
 /* b_contig_space() : returns the amount of bytes that can be appended to the
- * buffer at once.
+ * buffer at once. We have 8 possible cases :
+ *
+ * [____________________]  return size
+ * [______|_____________]  return size - tail_ofs
+ * [XXXXXX|_____________]  return size - tail_ofs
+ * [___|XXXXXX|_________]  return size - tail_ofs
+ * [______________XXXXXX]  return head_ofs
+ * [XXXX|___________|XXX]  return head_ofs - tail_ofs
+ * [XXXXXXXXXX|XXXXXXXXX]  return 0
+ * [XXXXXXXXXXXXXXXXXXXX]  return 0
  */
 static inline size_t b_contig_space(const struct buffer *b)
 {
-       const char *left, *right;
+       size_t left, right;
 
-       right = b_head(b);
+       right = b_head_ofs(b);
        left  = right + b_data(b);
 
-       if (left >= b_wrap(b))
-               left -= b_size(b);
-       else
-               right = b_wrap(b);
-
-       return right - left;
+       left = b_size(b) - left;
+       if ((ssize_t)left <= 0)
+               left += right;
+       return left;
 }
 
 /* b_getblk() : gets one full block of data at once from a buffer, starting