Implement efficient 'scm_unget_bytes' and 'unget-bytevector'.

* libguile/ports.c (scm_i_unget_bytes): New static function.
  (scm_unget_bytes): New API function.
  (scm_unget_byte): Rewrite to simply call 'scm_i_unget_bytes'.
  (scm_ungetc, scm_peek_char, looking_at_bytes): Use 'scm_i_unget_bytes'.

* libguile/ports.h: Add prototype for 'scm_unget_bytes'.

* libguile/fports.c (scm_setvbuf): Use 'scm_unget_bytes'.

* libguile/r6rs-ports.c (scm_unget_bytevector): New procedure.

* module/ice-9/binary-ports.scm (unget-bytevector): New export.

* doc/ref/api-io.texi (R6RS Binary Input): Add documentation.
  (R6RS I/O Ports): Update brief description of (ice-9 binary-ports) to
  reflect the new reality: it is no longer a subset of (rnrs io ports).

* test-suite/tests/ports.test ("unget-bytevector"): Add test.

1 files changed, 16 insertions, 3 deletions

diff --git a/doc/ref/api-io.texi b/doc/ref/api-io.texi
index e994cd74b..948316678 100644
--- a/doc/ref/api-io.texi
+++ b/doc/ref/api-io.texi
@@ -1223,9 +1223,10 @@ possible.
 * R6RS Textual Output::         Textual output.
 @end menu
 
-A subset of the @code{(rnrs io ports)} module is provided by the
-@code{(ice-9 binary-ports)} module.  It contains binary input/output
-procedures and does not rely on R6RS support.
+A subset of the @code{(rnrs io ports)} module, plus one non-standard
+procedure @code{unget-bytevector} (@pxref{R6RS Binary Input}), is
+provided by the @code{(ice-9 binary-ports)} module.  It contains binary
+input/output procedures and does not rely on R6RS support.
 
 @node R6RS File Names
 @subsubsection File Names
@@ -1855,6 +1856,18 @@ reached.  Return either a new bytevector containing the data read or the
 end-of-file object (if no data were available).
 @end deffn
 
+The @code{(ice-9 binary-ports)} module provides the following procedure
+as an extension to @code{(rnrs io ports)}:
+
+@deffn {Scheme Procedure} unget-bytevector port bv [start [count]]
+@deffnx {C Function} scm_unget_bytevector (port, bv, start, count)
+Place the contents of @var{bv} in @var{port}, optionally starting at
+index @var{start} and limiting to @var{count} octets, so that its bytes
+will be read from left-to-right as the next bytes from @var{port} during
+subsequent read operations.  If called multiple times, the unread bytes
+will be read again in last-in first-out order.
+@end deffn
+
 @node R6RS Textual Input
 @subsubsection Textual Input