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| author | vlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4> | 2020-03-26 00:17:17 +0000 |
|---|---|---|
| committer | vlefevre <vlefevre@280ebfd0-de03-0410-8827-d642c229c3f4> | 2020-03-26 00:17:17 +0000 |
| commit | 2caa79803f1d5b1e29ef9712bf40c7c6f67a339c (patch) | |
| tree | fa4957837694202ef0656fb610297feda9309aba | |
| parent | 7572f822b6dda7fc5f93d7136b5d73f9808417df (diff) | |
| download | mpfr-2caa79803f1d5b1e29ef9712bf40c7c6f67a339c.tar.gz | |
[src/mpfr-impl.h] UBF: updated comment: this breaks aliasing rules, but
there isn't any other acceptable solution.
Note: when trying to build MPFR without --enable-assert, with GCC and
CFLAGS="-O2 -Werror=strict-aliasing", the compilation of tests/tsub.c
currently fails because of that.
git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@13816 280ebfd0-de03-0410-8827-d642c229c3f4
| -rw-r--r-- | src/mpfr-impl.h | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/src/mpfr-impl.h b/src/mpfr-impl.h index 4465b96eb..cb7c752a5 100644 --- a/src/mpfr-impl.h +++ b/src/mpfr-impl.h @@ -2526,9 +2526,11 @@ extern "C" { which is assumed to be present (with a value in it) when the usual exponent field has the value MPFR_EXP_UBF. The goal of this compatible representation is to easily be able to support UBF in "normal" code - and hopefully avoid aliasing issues at the same time. And code that - accepts UBF in input should also accept mpfr_t as a consequence; this - makes mpfr_t to UBF conversion unnecessary. + using the public API. This is some form of "subtyping". + + Unfortunately this breaks aliasing rules, and C does not provide any way + to avoid that (except with additional syntax ugliness and API breakage): + https://news.ycombinator.com/item?id=11753236 The alignment requirement for __mpfr_ubf_struct (UBF) needs to be at least as strong as the one for __mpfr_struct (MPFR number); this is not required |