--- Comment #9 from gcc-bugzilla at contacts dot eelis dot net 2008-08-13
22:24 ---
Ok, I see. Sorry for wasting your time.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37119
--- Comment #8 from rguenth at gcc dot gnu dot org 2008-08-13 22:20 ---
The relevant ABI says
"a bit-field mut entirely reside in a storage unit appropriate for
its declared type"
which means it all makes very much sense.
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rguenth at gcc dot gnu dot org changed:
Wha
--- Comment #7 from pinskia at gcc dot gnu dot org 2008-08-13 22:16 ---
>brings it down to 5 bytes (we seem to never pack chars with other types)
We do, but we don't packed if it overflows into the next unit.
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pinskia at gcc dot gnu dot org changed:
What|Remov
--- Comment #6 from rguenth at gcc dot gnu dot org 2008-08-13 22:05 ---
struct X { uint32_t a:17; uint8_t b:8; uint8_t c:1; } __attribute__((packed));
brings it down to 5 bytes (we seem to never pack chars with other types)
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37119
--- Comment #5 from rguenth at gcc dot gnu dot org 2008-08-13 22:01 ---
This is also 4 bytes in size:
struct X { uint32_t a:17; uint16_t b:8; uint16_t c:1; };
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37119
--- Comment #4 from rguenth at gcc dot gnu dot org 2008-08-13 21:59 ---
Seems like we do that since forever, so we cannot change this anyway. But
surely it looks unintuitive that
struct X { uint32_t a:17; uint16_t b:8; uint8_t c:1; };
is 4 bytes while
struct X { uint32_t a:17; uint8_
--- Comment #3 from pinskia at gcc dot gnu dot org 2008-08-13 21:43 ---
>I don't follow. 4 bytes is 4*8=32 bits, which is more than 26, no?
Or the ABI says the different types are not merged together. Really you have
to look into what the ABI says to figure out the correct answer. I d
--- Comment #2 from gcc-bugzilla at contacts dot eelis dot net 2008-08-13
21:39 ---
(In reply to comment #1)
> so 26bits which is a little over 4 bytes.
I don't follow. 4 bytes is 4*8=32 bits, which is more than 26, no?
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37119
--- Comment #1 from pinskia at gcc dot gnu dot org 2008-08-13 21:26 ---
> struct X { uint32_t a:17; uint8_t b:8; bool c:1; };
0...16 is a as uint32_t is more than 17 bytes
17...24 is b as uint8_t is 8 bytes
25...26 is c as bool is 1 byte
so 26bits which is a little over 4 bytes. so it
