GCC 8.0.0 Status Report (2018-01-15), Trunk in Regression and Documentation fixes only mode
Tue Feb 6 17:32:00 GMT 2018
On Tue, 6 Feb 2018, Vincent Lefevre wrote:
> The issues were also present on 64-bit platforms and were due to
> a bug in mpfr_div_ui, which has always been present, since 1999.
> With MPFR 4.0.0, they are also visible with mpfr_div just because
> mpfr_div now uses mpfr_div_ui in some simple cases. I don't think
> that GCC could be affected because AFAIK, a failure can only occur
> when the input and output precisions are different, or is this
> possible with GCC?
GCC doesn't use mpfr_div at all; it uses MPFR to fold calls to a range of
libm functions with constant arguments (input and output precisions should
always be the same, since GCC doesn't yet support built-in functions for
the TS 18661-1 narrowing functions such as fsqrtl), and for correctly
rounding conversions of decimal strings to binary floating point. The + -
* / operations are handled directly in real.c without use of MPFR. Of
course MPFR functions called might use mpfr_div indirectly.
Joseph S. Myers
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