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[Emacs-diffs] master c1c8b67: Check that signed right shift is arithmeti
From: |
Paul Eggert |
Subject: |
[Emacs-diffs] master c1c8b67: Check that signed right shift is arithmetic |
Date: |
Fri, 19 May 2017 16:43:42 -0400 (EDT) |
branch: master
commit c1c8b67246c4314b302cca2ac43f13a0baba4c16
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>
Check that signed right shift is arithmetic
* src/data.c (ash_lsh_impl): Verify that signed right shift is
arithmetic; if we run across a compiler that uses a logical shift
we’ll need to complicate the code before removing this
compile-time check. Help the compiler do common subexpression
elimination better.
---
src/data.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/src/data.c b/src/data.c
index 3ff2a80..4242b90 100644
--- a/src/data.c
+++ b/src/data.c
@@ -3066,9 +3066,12 @@ usage: (logxor &rest INTS-OR-MARKERS) */)
}
static Lisp_Object
-ash_lsh_impl (register Lisp_Object value, Lisp_Object count, bool lsh)
+ash_lsh_impl (Lisp_Object value, Lisp_Object count, bool lsh)
{
- register Lisp_Object val;
+ /* This code assumes that signed right shifts are arithmetic. */
+ verify ((EMACS_INT) -1 >> 1 == -1);
+
+ Lisp_Object val;
CHECK_NUMBER (value);
CHECK_NUMBER (count);
@@ -3076,12 +3079,12 @@ ash_lsh_impl (register Lisp_Object value, Lisp_Object
count, bool lsh)
if (XINT (count) >= EMACS_INT_WIDTH)
XSETINT (val, 0);
else if (XINT (count) > 0)
- XSETINT (val, XUINT (value) << XFASTINT (count));
+ XSETINT (val, XUINT (value) << XINT (count));
else if (XINT (count) <= -EMACS_INT_WIDTH)
XSETINT (val, lsh ? 0 : XINT (value) < 0 ? -1 : 0);
else
- XSETINT (val, lsh ? XUINT (value) >> -XINT (count) : \
- XINT (value) >> -XINT (count));
+ XSETINT (val, (lsh ? XUINT (value) >> -XINT (count)
+ : XINT (value) >> -XINT (count)));
return val;
}
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