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author | Hannes Domani <ssbssa@yahoo.de> | 2024-06-11 20:32:27 +0200 |
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committer | Hannes Domani <ssbssa@yahoo.de> | 2024-06-11 20:36:34 +0200 |
commit | d17731525424349d7e63b517acf9f45114979fbb (patch) | |
tree | 551ab6e2d134944cc2b81fb84fe073ef27b67d91 /gdb/testsuite | |
parent | 4bafd5b7f377bac19a6dad748f6a162556696c01 (diff) | |
download | binutils-d17731525424349d7e63b517acf9f45114979fbb.zip binutils-d17731525424349d7e63b517acf9f45114979fbb.tar.gz binutils-d17731525424349d7e63b517acf9f45114979fbb.tar.bz2 |
Fix right shift of negative numbers
PR31590 shows that right shift of negative numbers doesn't work
correctly since GDB 14:
(gdb) p (-3) >> 1
$1 = -1
GDB 13 and earlier returned the correct value -2.
And there actually is one test that shows the failure:
print -1 >> 1
$84 = 0
(gdb) FAIL: gdb.base/bitshift.exp: lang=asm: rsh neg lhs: print -1 >> 1
The problem was introduced with the change to gmp functions in
commit 303a881f87.
It's wrong because gdb_mpz::operator>> uses mpz_tdif_q_2exp, which
always rounds toward zero, and the gmp docu says this:
For positive n both mpz_fdiv_q_2exp and mpz_tdiv_q_2exp are simple
bitwise right shifts.
For negative n, mpz_fdiv_q_2exp is effectively an arithmetic right shift
treating n as two's complement the same as the bitwise logical functions
do, whereas mpz_tdiv_q_2exp effectively treats n as sign and magnitude.
So this changes mpz_tdiv_q_2exp to mpz_fdiv_q_2exp, since it
does right shifts for both positive and negative numbers.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31590
Approved-By: Tom Tromey <tom@tromey.com>
Diffstat (limited to 'gdb/testsuite')
-rw-r--r-- | gdb/testsuite/gdb.base/bitshift.exp | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/gdb/testsuite/gdb.base/bitshift.exp b/gdb/testsuite/gdb.base/bitshift.exp index 61c7eca..17f6b78 100644 --- a/gdb/testsuite/gdb.base/bitshift.exp +++ b/gdb/testsuite/gdb.base/bitshift.exp @@ -344,6 +344,8 @@ proc test_shifts {} { with_test_prefix "rsh neg lhs" { test_shift $lang "print -1 >> 0" " = -1" test_shift $lang "print -1 >> 1" " = -1" + test_shift $lang "print -2 >> 1" " = -1" + test_shift $lang "print -3 >> 1" " = -2" test_shift $lang "print -8 >> 1" " = -4" test_shift $lang "print [make_int64 $lang -8] >> 1" " = -4" } |