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| author | Kaz Kylheku <kaz@kylheku.com> | 2022-05-24 06:49:51 -0700 |
|---|---|---|
| committer | Kaz Kylheku <kaz@kylheku.com> | 2022-05-24 06:49:51 -0700 |
| commit | 735a001aece9e7b7247561201e63c7efa93b3bee (patch) | |
| tree | 716224bd7ded4e43245704fef8651b4db8dd7911 | |
| parent | 2262860404bad7755c6a8adb10f167439037f3fa (diff) | |
| download | txr-735a001aece9e7b7247561201e63c7efa93b3bee.tar.gz txr-735a001aece9e7b7247561201e63c7efa93b3bee.tar.bz2 txr-735a001aece9e7b7247561201e63c7efa93b3bee.zip | |
doc: add a note about pack.
* txr.1: pack with alignment values greater than 1 doesn't
directly correspond to a single GNU C feature.
| -rw-r--r-- | txr.1 | 34 |
1 files changed, 34 insertions, 0 deletions
@@ -81476,6 +81476,40 @@ After these transformations are applied, the nested forms which occur in the transformed syntax may perform more such transformations, depending on their operands. +Note that the two-argument form of +.code pack +with a +.meta width +value greater than 1 doesn't directly correspond to any +single attribute specifier in GNU C. The GNU C +.code packed +attribute is Boolean, implicitly reducing alignment to 1. +A combination of the GNU C attributes +.code aligned +and +.code packed +is used to produce the effect of +.mono +.meti (pack < n << type ) +.onom +for values of +.meta n +> 1. +In GNU C, the +.code packed +attribute, when applied to a structure, distributes to its members, +but isn't capable of distributing an alignment exceeding 1. So the +.mono +.meti (pack < n (struct ...)) +.onom +expression, for values of +.meta n +> 1, doesn't correspond to anything in GNU C; its effect +can be simulated by attributing the structure type with +.codn packed , +and then individually applying the required alignment to +the member declarations. + .SS* Additional Types .coNP FFI types @, size-t @, ptrdiff-t @, int-ptr-t @, uint-ptr-t @, intmax-t @, uintmax-t @ wint-t @, sig-atomic-t @ time-t and @ clock-t .desc |