Author: Dieter Buerssner
Date: 08:12:10 12/09/02
Go up one level in this thread
On December 09, 2002 at 10:11:54, Matt Taylor wrote:
>>Thanks. Could not find the "1f" or "1b" stuff anywhere on the web or in the gcc
>>docs/info pages.
>>
>>Bob
>
>I've never seen that particular behavior documented, but I know the 1f/2f/1b
>stuff is common in GNU assembly.
It is documented in the GNU assembler manual:
---
Local Symbol Names
------------------
Local symbols help compilers and programmers use names temporarily.
They create symbols which are guaranteed to be unique over the entire
scope of the input source code and which can be referred to by a simple
notation. To define a local symbol, write a label of the form `N:'
(where N represents any positive integer). To refer to the most recent
previous definition of that symbol write `Nb', using the same number as
when you defined the label. To refer to the next definition of a local
label, write `Nf'-- The `b' stands for"backwards" and the `f' stands
for "forwards".
There is no restriction on how you can use these labels, and you can
reuse them too. So that it is possible to repeatedly define the same
local label (using the same number `N'), although you can only refer to
the most recently defined local label of that number (for a backwards
reference) or the next definition of a specific local label for a
forward reference. It is also worth noting that the first 10 local
labels (`0:'...`9:') are implemented in a slightly more efficient
manner than the others.
Here is an example:
1: branch 1f
2: branch 1b
1: branch 2f
2: branch 1b
Which is the equivalent of:
label_1: branch label_3
label_2: branch label_1
label_3: branch label_4
label_4: branch label_3
[...]
---
There is a small contradiction: "N repreresents any positive integer"
and later: "the first 10 local labels (`0:'...`9:')"
>I would have suggested nasm syntax, but that wouldn't get inlined,
>unfortunately.
gcc cannot produce nasm output from C-code. I guess the inlining part would
actually work - but wouldn't be of any help, of course.
Regards,
Dieter
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