This patch optimizes the md5_text() function (which is used to

implement the md5() SQL-level function). The old code did the
following:

1. de-toast the datum
2. convert it to a cstring via textout()
3. get the length of the cstring via strlen()

Since we are treating the datum context as a blob of binary data,
the latter two steps are unnecessary. Once the data has been
detoasted, we can just use it as-is, and derive its length from
the varlena metadata.

This patch improves some run-of-the-mill md5() computations by
just under 10% in my limited tests, and passes the regression tests.

I also noticed that md5_text() wasn't checking the return value
of md5_hash(); encountering OOM at precisely the right moment
could result in returning a random md5 hash. This patch corrects
that. A better fix would be to make md5_hash() only return on
success (and/or allocate via palloc()), but since it's used in
the frontend as well I don't see an easy way to do that.

src/backend/libpq/md5.c

@@ -14,7 +14,7 @@
  *	Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/libpq/md5.c,v 1.27 2004/12/31 21:59:50 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/libpq/md5.c,v 1.28 2005/02/23 22:46:17 neilc Exp $
  */
 
 
@@ -289,8 +289,8 @@ bytesToHex(uint8 b[16], char *s)
  *						  characters.  you thus need to provide an array
  *						  of 33 characters, including the trailing '\0'.
  *
- *	RETURNS		  0 on failure (out of memory for internal buffers) or
- *				  non-zero on success.
+ *	RETURNS		  false on failure (out of memory for internal buffers) or
+ *				  true on success.
  *
  *	STANDARDS	  MD5 is described in RFC 1321.
  *