store: Rewrite 'store-path-hash-part' to not use regexps.

* guix/store.scm (store-path-hash-part): Rewrite without using a
regexp.  This speeds up 'guix substitute'.

1 files changed, 6 insertions, 3 deletions

diff --git a/guix/store.scm b/guix/store.scm
index b15da54852..2563d26fa0 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -1549,9 +1549,12 @@ valid inputs."
 (define (store-path-hash-part path)
   "Return the hash part of PATH as a base32 string, or #f if PATH is not a
 syntactically valid store path."
-  (let ((path-rx (store-regexp* (%store-prefix))))
-    (and=> (regexp-exec path-rx path)
-           (cut match:substring <> 1))))
+  (and (string-prefix? (%store-prefix) path)
+       (let ((base (string-drop path (+ 1 (string-length (%store-prefix))))))
+         (and (> (string-length base) 33)
+              (let ((hash (string-take base 32)))
+                (and (string-every %nix-base32-charset hash)
+                     hash))))))
 
 (define (log-file store file)
   "Return the build log file for FILE, or #f if none could be found.  FILE