Re: [PATCH] PR libstdc++/13045 / C++ demangler, floating values and function pointer type return type postfix fix.

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

Carlo Wood <carlo@alinoe.com> writes:

| On Wed, Nov 26, 2003 at 05:34:34AM +0100, Gabriel Dos Reis wrote:
| > It will not work. One reason was explained by DJ.
| 
| What reason was that?  I cannot remember to have read any
| valid reason from him.  Please include DETAILS in your
| mails or we will not get anywhere. (like this:)
| 
| If you are refering to his remark in
| http://gcc.gnu.org/ml/gcc-patches/2003-11/msg02054.html
| then you didn't read my original proposal either.
| 
| Perhaps I am too mathematical orientated; when I talk

I can speak mathematics too.

| about a one-on-one bijection, then I use the words
| "*exactly* as typed by the programmer", because in my
| mind, a 100% reversable one-on-one character translation
| is it is equivalent, there is no difference abstractly
| seen.

Sure, there is a difference.  The mangling is not
character-for-character  oriented but toekn-for-token oriented.
Which is where you and me differ.

|  Sorry if I was unclear in my choice of words;
| nevertheless, I was more then clear in my examples later
| in that same post.
| 
| > Another is that
| > it does not reduce to a normal form before outputing leading to many
| > symbols being thought different while they are the same.
| 
| But is that really a problem?

the same that lead to the current thread, i.e. trying to use a
character oriented meaning where a token-oriented understanding is
used. 

|  Because when it is a problem
| then there a lot more problems just around the corner (see below).
| 
| > It is not like no other concrete and praticable proposal was made.
| > 
| > The C99 hex floating notation notation with the constraints
| >   (1) no trailing zero for mantissa
| >   (2) no leading zero for exponent
| > gives a normal form (or pretty close -- double check).
| > It has the advantage of being target independent.
| 
| That is not correct.  On different targets, this can result in
| different symbols.  For example, a floating point value that cannot
| be represented in a finite number of binary bits will result in
| different symbols depending on the precision of a double on that target.
| 
| For example, suppose the programmer types in the source code: "1.234".
| Then on one target that could result in:
| 1.3BE76C9 and on another 1.3BE76C8B43958

Since the mangler and the demangler use the same hex encodings.

| the demangler would translate the last one into:
| 
| 1.234  (because it is 1.2339999999999999857...,
|                                        ^__ last digit needed for given
| 				           precision.

The demangler will translate back exactly what the mangler put there.

-- Gaby