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[Guile-commits] branch master updated: Optimize truncate-bits
From: |
Andy Wingo |
Subject: |
[Guile-commits] branch master updated: Optimize truncate-bits |
Date: |
Thu, 06 May 2021 15:52:15 -0400 |
This is an automated email from the git hooks/post-receive script.
wingo pushed a commit to branch master
in repository guile.
The following commit(s) were added to refs/heads/master by this push:
new 05614f7 Optimize truncate-bits
05614f7 is described below
commit 05614f792bfabbc33798863edd0bb67c744e9299
Author: Andy Wingo <wingo@pobox.com>
AuthorDate: Thu May 6 21:49:13 2021 +0200
Optimize truncate-bits
* module/system/base/types/internal.scm (truncate-bits): Inline cases
for 16, 32, and 64, to avoid allocating bignums for the boundary
conditions.
---
module/system/base/types/internal.scm | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/module/system/base/types/internal.scm
b/module/system/base/types/internal.scm
index c75ca3b..0514d7b 100644
--- a/module/system/base/types/internal.scm
+++ b/module/system/base/types/internal.scm
@@ -1,5 +1,5 @@
;;; Details on internal value representation.
-;;; Copyright (C) 2014, 2015, 2017, 2018, 2020 Free Software Foundation, Inc.
+;;; Copyright (C) 2014, 2015, 2017, 2018, 2020, 2021 Free Software Foundation,
Inc.
;;;
;;; This library is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as published by
@@ -230,9 +230,22 @@ may not fit into a word on the target platform."
(else (error "value does not fit in bits" x bits))))
(define (truncate-bits x bits signed?)
- (let ((x' (logand x (1- (ash 1 bits)))))
- (and (eq? x (if signed? (sign-extend x' bits) x'))
- x')))
+ (define-syntax-rule (bits-case bits)
+ (let ((umax (1- (ash 1 bits)))
+ (smin (ash -1 (1- bits)))
+ (smax (1- (ash 1 (1- bits)))))
+ (and (if signed?
+ (<= smin x smax)
+ (<= 0 x umax))
+ (logand x umax))))
+ (case bits
+ ((16) (bits-case 16))
+ ((32) (bits-case 32))
+ ((64) (bits-case 64))
+ (else
+ (let ((x' (logand x (1- (ash 1 bits)))))
+ (and (eq? x (if signed? (sign-extend x' bits) x'))
+ x')))))
;; See discussion in tags.h and boolean.h.
(eval-when (expand)
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