X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~mdw/git/mLib/blobdiff_plain/beee81ec8fc4857080e809c759575c4267f7bd1f..d93e9a33ee30faed3945b2a7acfc46b84197d432:/struct/buf.c

diff --git a/struct/buf.c b/struct/buf.c
index 4b02b28..10e0544 100644
--- a/struct/buf.c
+++ b/struct/buf.c
@@ -223,6 +223,60 @@ int buf_fill(buf *b, int ch, size_t sz)
 int (dbuf_fill)(dbuf *db, int ch, size_t sz)
   { return (dbuf_fill(db, ch, sz)); }
 
+/* --- @align_step@ --- *
+ *
+ * Arguments:	@buf *b@ = pointer to a buffer block
+ *		@size_t m, a@ = alignment parameters
+ *
+ * Returns:	The number of bytes to skip or fill.
+ */
+
+static size_t align_step(buf *b, size_t m, size_t a)
+{
+  if (m < 2) return (0);
+  else if (!(m&(m - 1))) return ((a - BLEN(b))&(m - 1));
+  else return ((a + m - BLEN(b)%m)%m);
+}
+
+/* --- @{,d}buf_alignskip@ --- *
+ *
+ * Arguments:	@buf *b@ or @dbuf *db@ = pointer to a buffer block
+ *		@size_t m, a@ = alignment multiple and offset
+ *
+ * Returns:	Zero if it worked, nonzero if there wasn't enough space.
+ *
+ * Use:		Advance the buffer position as little as possible such that
+ *		it is @a@ greater than a multiple of @m@.  This doesn't write
+ *		anything to the buffer, so it's probably not suitable for
+ *		output: use @buf_alignfill@ instead.
+ */
+
+int buf_alignskip(buf *b, size_t m, size_t a)
+{
+  if (!buf_get(b, align_step(b, m, a))) return (-1);
+  else return (0);
+}
+int (dbuf_alignskip)(dbuf *db, size_t m, size_t a)
+  { return (dbuf_alignskip(db, m, a)); }
+
+/* --- @{,d}buf_alignfill@ --- *
+ *
+ * Arguments:	@buf *b@ or @dbuf *db@ = pointer to a buffer block
+ *		@int ch@ = fill character
+ *		@size_t m, a@ = alignment multiple and offset
+ *
+ * Returns:	Zero if it worked, nonzero if there wasn't enough space.
+ *
+ * Use:		Fill the buffer with as few copies of @ch@ as possible, as if
+ *		by @memset@, to advance the buffer position to a value @a@
+ *		greater than a multiple of @m@.
+ */
+
+int buf_alignfill(buf *b, int ch, size_t m, size_t a)
+  { return (buf_fill(b, ch, align_step(b, m, a))); }
+int (dbuf_alignfill)(dbuf *db, int ch, size_t m, size_t a)
+  { return (dbuf_alignfill(db, ch, m, a)); }
+
 /* --- @{,d}buf_getbyte@ --- *
  *
  * Arguments:	@buf *b@ or @dbuf *db@ = pointer to a buffer block