g10/plaintext: do_hash: use iobuf_read for higher performance

* g10/plaintext.c (do_hash): Use iobuf_read instead of iobuf_get for
reading data; Use gcry_md_write instead of gcry_md_putc for hash data.
--

This patch reduces iobuf_read per byte processing overhead and speeds
up detached signature verifying.

Detached verifying speed on AMD Ryzen 5800X (4.3GiB file, SHA256):

         gpg process
         user time
 before: 9.410s
 after:  1.913s (4.9x faster)

GnuPG-bug-id: T5826
Signed-off-by: Jussi Kivilinna <[email protected]>

1 files changed, 7 insertions, 2 deletions

diff --git a/g10/plaintext.c b/g10/plaintext.c
index 3e169d93f..f20057cbb 100644
--- a/g10/plaintext.c
+++ b/g10/plaintext.c
@@ -545,11 +545,16 @@ do_hash (gcry_md_hd_t md, gcry_md_hd_t md2, IOBUF fp, int textmode)
     }
   else
     {
-      while ((c = iobuf_get (fp)) != -1)
+      byte *buffer = xmalloc (32768);
+      int ret;
+
+      while ((ret = iobuf_read (fp, buffer, 32768)) != -1)
 	{
 	  if (md)
-	    gcry_md_putc (md, c);
+	    gcry_md_write (md, buffer, ret);
 	}
+
+      xfree (buffer);
     }
 }