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| author | Eric Botcazou <ebotcazou@adacore.com> | 2020-04-13 11:10:43 +0200 |
|---|---|---|
| committer | Pierre-Marie de Rodat <derodat@adacore.com> | 2020-06-17 04:14:04 -0400 |
| commit | 741826eff5855366c65d49123b899ea40fc0c443 (patch) | |
| tree | f5540a6179e08cdf3f363c3081d9f2118b1c9632 /gcc/ada/doc | |
| parent | d27ec3f60a3ac5eab05765cbbf45083e4e3dabc6 (diff) | |
| download | gcc-741826eff5855366c65d49123b899ea40fc0c443.zip gcc-741826eff5855366c65d49123b899ea40fc0c443.tar.gz gcc-741826eff5855366c65d49123b899ea40fc0c443.tar.bz2 | |
[Ada] Adjust documentation of 'Bit and 'Descriptor_Size attributes
2020-06-17 Eric Botcazou <ebotcazou@adacore.com>
gcc/ada/
* doc/gnat_rm/implementation_defined_attributes.rst (Bit): Sharpen
the comparison with System.Storage_Unit.
(Descriptor_Size): Clear confusion about alignment and padding.
* gnat_rm.texi: Regenerate.
Diffstat (limited to 'gcc/ada/doc')
| -rw-r--r-- | gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst b/gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst index e285ebc..cfde81e 100644 --- a/gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst +++ b/gcc/ada/doc/gnat_rm/implementation_defined_attributes.rst @@ -93,8 +93,8 @@ Attribute Bit ``obj'Bit``, where ``obj`` is any object, yields the bit offset within the storage unit (byte) that contains the first bit of storage allocated for the object. The value of this attribute is of the -type *universal_integer*, and is always a non-negative number not -exceeding the value of ``System.Storage_Unit``. +type *universal_integer* and is always a nonnegative number smaller +than ``System.Storage_Unit``. For an object that is a variable or a constant allocated in a register, the value is zero. (The use of this attribute does not force the @@ -241,14 +241,16 @@ the first element of the array. .. code-block:: ada - type Unconstr_Array is array (Positive range <>) of Boolean; + type Unconstr_Array is array (Short_Short_Integer range <>) of Positive; Put_Line ("Descriptor size = " & Unconstr_Array'Descriptor_Size'Img); -The attribute takes into account any additional padding due to type alignment. -In the example above, the descriptor contains two values of type -``Positive`` representing the low and high bound. Since ``Positive`` has -a size of 31 bits and an alignment of 4, the descriptor size is ``2 * Positive'Size + 2`` or 64 bits. +The attribute takes into account any padding due to the alignment of the +component type. In the example above, the descriptor contains two values +of type ``Short_Short_Integer`` representing the low and high bound. But, +since ``Positive`` has an alignment of 4, the size of the descriptor is +``2 * Short_Short_Integer'Size`` rounded up to the next multiple of 32, +which yields a size of 32 bits, i.e. including 16 bits of padding. Attribute Elaborated ==================== |