Implement real literal extension for Ada

Sometimes it is convenient to be able to specify the exact bits of a
floating-point literal.  For example, you may want to set a
floating-point register to a denormalized value, or to a particular
NaN.

In C, you can do this by combining the "{}" cast with an array
literal, like:

    (gdb) p {double}{0x576488BDD2AE9FFE}
    $1 = 9.8765449999999996e+112

This patch adds a somewhat similar idea to Ada.  It extends the lexer
to allow "l" and "f" suffixes in a based literal.  The "f" indicates a
floating-point literal, and the "l"s control the size of the
floating-point type.

Note that this differs from Ada's based real literals.  I believe
those can also be used to control the bits of a floating-point value,
but they are a bit more cumbersome to use (simplest is binary but
that's also very lengthy).  Also, these aren't implemented in GDB.

I chose not to allow this extension to work with based integer
literals with exponents.  That didn't seem very useful.

1 files changed, 8 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 068a6c46bc8..8fce31c41f1 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -142,6 +142,14 @@ info win
   This command now includes information about the width of the tui
   windows in its output.
 
+* GDB's Ada parser now supports an extension for specifying the exact
+  byte contents of a floating-point literal.  This can be useful for
+  setting floating-point registers to a precise value without loss of
+  precision.  The syntax is an extension of the based literal syntax.
+  Use, e.g., "16lf#0123abcd#" -- the number of "l"s controls the width
+  of the floating-point type, and the "f" is the marker for floating
+  point.
+
 * New targets
 
 GNU/Linux/LoongArch    loongarch*-*-linux*