On 8/20/23 16:11, Bruno Haible wrote:
The new code not only assume two's complement, but also that
right-shift of negative 'int' works as in two's complement.
It's easy enough to remove that assumption, and this makes the code a
bit simpler, and not significantly less efficient since GCC implements N
% 2 and N / 2 by masking and shifting. I installed the attached.From 3703c742aa9b90d57bc7427b94cec21a6492d106 Mon Sep 17 00:00:00 2001
From: Paul Eggert <[email protected]>
Date: Sun, 20 Aug 2023 17:55:03 -0700
Subject: [PATCH] =?UTF-8?q?ldexp:=20port=20to=20non-two=E2=80=99s=20comple?=
=?UTF-8?q?ment?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
* lib/ldexp.c (FUNC): Don’t assume two’s-complement.
---
ChangeLog | 5 +++++
lib/ldexp.c | 9 ++++-----
2 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 6575ee12b6..8f346acff5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2023-08-20 Paul Eggert <[email protected]>
+
+ ldexp: port to non-two’s complement
+ * lib/ldexp.c (FUNC): Don’t assume two’s-complement.
+
2023-08-20 Bruno Haible <[email protected]>
readutmp, boot-time: Fix the result on runit and s6 init systems.
diff --git a/lib/ldexp.c b/lib/ldexp.c
index 844fd11f53..8bc4073527 100644
--- a/lib/ldexp.c
+++ b/lib/ldexp.c
@@ -57,16 +57,15 @@ FUNC (DOUBLE x, int exp)
BEGIN_ROUNDING ();
/* Check for zero, nan and infinity. */
- if (!(ISNAN (x) || x + x == x || exp == 0))
+ if (!(ISNAN (x) || x + x == x))
{
- bool negexp = exp < 0;
- DOUBLE factor = negexp ? L_(0.5) : L_(2.0);
+ DOUBLE factor = exp < 0 ? L_(0.5) : L_(2.0);
while (true)
{
- if (exp & 1)
+ if (exp % 2 != 0)
x *= factor;
- exp = (exp + negexp) >> 1;
+ exp /= 2;
if (exp == 0)
break;
factor = factor * factor;
--
2.41.0
