Doc update to mention MPFR (Re: [RFC][00/19] Target FP: Precise target floating-point emulation)

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Eli Zaretskii wrote:
> > Date: Thu, 16 Nov 2017 20:05:59 +0100 (CET)
> > From: "Ulrich Weigand" <uweigand@de.ibm.com>
> > Cc: eliz@gnu.org (Eli Zaretskii), gdb-patches@sourceware.org
> > 
> > I've just posted an updated set of patches that implements the
> > suggestion to use host FP if the format matches, and MPFR if not.
> > To keep code complexity down, this is done by encapsulating the
> > operations in an abstract base class with multiple implementations.
> > https://sourceware.org/ml/gdb-patches/2017-11/msg00323.html
> > https://sourceware.org/ml/gdb-patches/2017-11/msg00324.html
> > 
> > Does this address your concerns?
> 
> Yes, thank you very much.

Thanks for confirming!

I just noticed that I forgot to update the docs to mention MPFR.
The following patch adds this to README and gdb.texinfo in the
same places where libexpat is mentioned.  It also add a brief
mention to NEWS.

Is this OK?

Thanks,
Ulrich


gdb/ChangeLog:

	* NEWS: Document use of GNU MPFR.
	* README: Likewise.
	* doc/gdb.texinfo: Likewise

Index: binutils-gdb/gdb/NEWS
===================================================================
--- binutils-gdb.orig/gdb/NEWS
+++ binutils-gdb/gdb/NEWS
@@ -3,6 +3,10 @@
 
 *** Changes since GDB 8.0
 
+* GDB now uses the GNU MPFR library, if available, to emulate target
+  floating-point arithmetic during expression evaluation when the target
+  uses different floating-point formats than the host.
+
 * GDB now supports access to the guarded-storage-control registers and the
   software-based guarded-storage broadcast control registers on IBM z14.
 
Index: binutils-gdb/gdb/README
===================================================================
--- binutils-gdb.orig/gdb/README
+++ binutils-gdb/gdb/README
@@ -89,6 +89,15 @@ features.  Expat will be linked in if it
 those features will be disabled.  The latest version of Expat should be
 available from `http://expat.sourceforge.net'.
 
+   GDB uses GNU MPFR, a library for multiple-precision floating-point
+computation with correct rounding, to emulate target floating-point
+arithmetic during expression evaluation when the target uses different
+floating-point formats than the host.  MPFR will be linked in if it is
+available at build time.  At least version 3.1 of GNU MPFR is required.
+If GNU MPFR it is not available, GDB will fall back to using host
+floating-point arithmetic.  The latest version of GNU MPFR should be
+available from `http://www.mpfr.org´;.
+
    GDB can be used as a cross-debugger, running on a machine of one
 type while debugging a program running on a machine of another type.
 See below.
@@ -475,6 +484,16 @@ prefer; but you may abbreviate option na
      have libexpat installed, you can  get the latest version from
      http://expat.sourceforge.net.
 
+`--with-mpfr'
+     Build GDB with the GNU MPFR library.  (Done by default if
+     GNU MPFR is installed and found at configure time.)  This library
+     is used to emulate target floating-point arithmetic during expression
+     evaluation when the target uses different floating-point formats than
+     the host. At least version 3.1 of GNU MPFR is required.  If GNU MPFR
+     is not available, GDB will fall back to using host floating-point
+     arithmetic.  If your host does not have GNU MPFR installed, you can
+     get the latest version from http://www.mpfr.org.
+
 `--with-python[=PATH]'
      Build GDB with Python scripting support.  (Done by default if
      libpython is present and found at configure time.)  Python makes
Index: binutils-gdb/gdb/doc/gdb.texinfo
===================================================================
--- binutils-gdb.orig/gdb/doc/gdb.texinfo
+++ binutils-gdb/gdb/doc/gdb.texinfo
@@ -34270,6 +34270,22 @@ Branch trace (@pxref{Branch Trace Format
 @pxref{Branch Trace Configuration Format})
 @end itemize
 
+@item MPFR
+@anchor{MPFR}
+@value{GDBN} can use the GNU MPFR multiple-precision floating-point
+library.  This library may be included with your operating system
+distribution; if it is not, you can get the latest version from
+@url{http://www.mpfr.org}.  At least version 3.1 of GNU MPFR is
+required.  The @file{configure} script will search for this library
+in several standard locations; if it is installed in an unusual path,
+you can use the @option{--with-libmpfr-prefix} option to specify
+its location.
+
+GNU MPFR is used to emulate target floating-point arithmetic during
+expression evaluation when the target uses different floating-point
+formats than the host.  If GNU MPFR it is not available, GDB will
+fall back to using host floating-point arithmetic.
+
 @item zlib
 @cindex compressed debug sections 
 @value{GDBN} will use the @samp{zlib} library, if available, to read


-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com