diff options
| author | Ludovic Courtès <ludo@gnu.org> | 2021-09-09 23:22:10 +0200 |
|---|---|---|
| committer | Ludovic Courtès <ludo@gnu.org> | 2021-09-10 17:30:54 +0200 |
| commit | cb06f7c61e4b8393abf38f1f5891e03c33d53b9b (patch) | |
| tree | 5ae33fcbe4a683a03cc7149caa819ad4bdbee4da /guix/base32.scm | |
| parent | a87d8c912d64382d8d7489c156249bc2b2638df0 (diff) | |
| download | guix-cb06f7c61e4b8393abf38f1f5891e03c33d53b9b.tar guix-cb06f7c61e4b8393abf38f1f5891e03c33d53b9b.tar.gz | |
base32: Provide an open-coded 'bit-field'.
This improves the throughput of 'bytevector->base32-string' a bit.
* guix/base32.scm (bit-field): New macro.
Diffstat (limited to 'guix/base32.scm')
| -rw-r--r-- | guix/base32.scm | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/guix/base32.scm b/guix/base32.scm index 49f191ba26..d6c8a02243 100644 --- a/guix/base32.scm +++ b/guix/base32.scm @@ -1,5 +1,5 @@ ;;; GNU Guix --- Functional package management for GNU -;;; Copyright © 2012, 2015, 2017 Ludovic Courtès <ludo@gnu.org> +;;; Copyright © 2012, 2015, 2017, 2021 Ludovic Courtès <ludo@gnu.org> ;;; ;;; This file is part of GNU Guix. ;;; @@ -42,6 +42,19 @@ ;;; ;;; Code: +(define-syntax bit-field + (lambda (s) + ;; This inline version of 'bit-field' assumes that START and END are + ;; literals and pre-computes the mask. In an ideal world, using 'define' + ;; or 'define-inlinable' would be enough, but as of 3.0.7, peval doesn't + ;; expand calls to 'expt' (and 'bit-field' is a subr.) + (syntax-case s () + ((_ n start end) + (let* ((s (syntax->datum #'start)) + (e (syntax->datum #'end)) + (mask (- (expt 2 (- e s)) 1))) + #`(logand (ash n (- start)) #,mask)))))) + (define bytevector-quintet-ref (let* ((ref bytevector-u8-ref) (ref+ (lambda (bv offset) |