02/04: openpgp: Use Libgcrypt's crc24 implementation.

[guix-commits]

civodul pushed a commit to branch master
in repository guix.

commit 6f233040d34706879a9ac490668a7132be4f1e13
Author: Ludovic Courtès <ludo@gnu.org>
AuthorDate: Tue Jun 23 18:11:35 2020 +0200

    openpgp: Use Libgcrypt's crc24 implementation.
    
    This gives an 18% speedup on the wall-clock time of:
    
      guile -c '(use-modules (git) (guix git-authenticate)) 
(load-keyring-from-reference (repository-open ".") "keyring")'
    
    * guix/openpgp.scm (crc24): Rewrite by calling out to 'bytevector-hash'.
---
 guix/openpgp.scm | 21 ++++-----------------
 1 file changed, 4 insertions(+), 17 deletions(-)

diff --git a/guix/openpgp.scm b/guix/openpgp.scm
index b74f8ff..33c8512 100644
--- a/guix/openpgp.scm
+++ b/guix/openpgp.scm
@@ -1029,23 +1029,10 @@ there is no limit."
 
 (define (crc24 bv)
   "Compute a CRC24 as described in RFC4880, Section 6.1."
-  (define poly #x1864cfb)
-
-  (let loop ((crc #xb704ce)
-             (index 0))
-    (if (= index (bytevector-length bv))
-        (logand crc #xffffff)
-        (let ((crc (logxor (ash (bytevector-u8-ref bv index) 16)
-                           crc)))
-          (let inner ((i 0)
-                      (crc crc))
-            (if (< i 8)
-                (let ((crc (ash crc 1)))
-                  (inner (+ i 1)
-                         (if (zero? (logand crc #x1000000))
-                             crc
-                             (logxor crc poly))))
-                (loop crc (+ index 1))))))))
+  ;; We used to have it implemented in Scheme but the C version here makes
+  ;; 'load-keyring-from-reference' 18% faster when loading the 72
+  ;; ASCII-armored files of today's Guix keyring.
+  (bytevector->uint (bytevector-hash bv (hash-algorithm crc24-rfc2440))))
 
 (define %begin-block-prefix "-----BEGIN ")
 (define %begin-block-suffix "-----")