sha256: allow application to specify digest buffer.

* chksum.c (sha256_stream_impl): New static function, formed
out of bulk of sha256_stream. Takes a pointer to a buffer
where the digest is stored.
(sha256_ensure_buf): New static function.
(sha256_stream): Take buf argument; use sha256_ensure_buf to
allocate a buffer if necessary, and to obtain the low-level
buffer pointer. Implementation moved into sha256_stream_impl.
(sha256_buf, sha256_str): Take pointer to digest buffer; don't
allocate a buf object, don't return anything.
(sha256): Take buf argument; use sha256_ensure_buf to
allocate a buffer if necessary, and to obtain the low-level
buffer pointer, which is passed to sha256_buf and sha256_str.
(chksum_init): Update registrations of intrinsics with new
optional parameters.

* chksum.h (sha256_stream, sha256): Declarations updated.

* txr.1: Updated.

1 files changed, 2 insertions, 2 deletions

diff --git a/chksum.h b/chksum.h
index e3516f57..6eb68588 100644
--- a/chksum.h
+++ b/chksum.h
@@ -25,8 +25,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-val sha256_stream(val stream, val nbytes);
-val sha256(val obj);
+val sha256_stream(val stream, val nbytes, val buf);
+val sha256(val obj, val buf);
 val crc32_stream(val stream, val nbytes);
 val crc32(val obj);
 void chksum_init(void);