crc32: add optional initial crc argument.

This allows a CRC-32 calculation over multiple objects in
multiple steps.

* chksum.c (crc32_stream, crc32_buf, crc32_str, crc32): Take
additional argument.
(chksum_init): Add optional argument to registration of
crc32-stream and crc32 intrinsics.

* chksum.h (crc32_stream, crc32): Declarations updated.

* txr.1: Doc updated; two examples added.

1 files changed, 2 insertions, 2 deletions

diff --git a/chksum.h b/chksum.h
index 6ec364e5..33cc9c67 100644
--- a/chksum.h
+++ b/chksum.h
@@ -30,8 +30,8 @@ val sha256(val obj, val buf);
 val sha256_begin(void);
 val sha256_hash(val ctx, val obj);
 val sha256_end(val ctx, val buf);
-val crc32_stream(val stream, val nbytes);
-val crc32(val obj);
+val crc32_stream(val stream, val nbytes, val init);
+val crc32(val obj, val init);
 val md5_stream(val stream, val nbytes, val buf);
 val md5(val obj, val buf_in);
 val md5_begin(void);