Struct loca::Layout [−][src]
pub struct Layout { /* fields omitted */ }Expand description
Layout of a block of memory.
An instance of Layout describes a particular layout of memory.
You build a Layout up as an input to give to an allocator.
All layouts have an associated non-negative size and a power-of-two alignment.
(Note however that layouts are not required to have positive
size, even though many allocators require that all memory
requests have positive size. A caller to the Alloc::alloc
method must either ensure that conditions like this are met, or
use specific allocators with looser requirements.)
Implementations
Constructs a Layout from a given size and align,
or returns None if any of the following conditions
are not met:
-
alignmust be a power of two, -
alignmust not exceed 2^31 (i.e.1 << 31), -
size, when rounded up to the nearest multiple ofalign, must not overflow (i.e. the rounded value must be less thanusize::MAX).
Creates a layout, bypassing all checks.
Safety
This function is unsafe as it does not verify that align is
a power-of-two that is also less than or equal to 2^31, nor
that size aligned to align fits within the address space
(i.e. the Layout::from_size_align preconditions).
The minimum byte alignment for a memory block of this layout.
Produces layout describing a record that could be used to
allocate backing structure for T (which could be a trait
or other unsized type like a slice).
Creates a layout describing the record that can hold a value
of the same layout as self, but that also is aligned to
alignment align (measured in bytes).
If self already meets the prescribed alignment, then returns
self.
Note that this method does not add any padding to the overall
size, regardless of whether the returned layout has a different
alignment. In other words, if K has size 16, K.align_to(32)
will still have size 16.
Panics
Panics if the combination of self.size and the given align
violates the conditions listed in from_size_align.
Returns the amount of padding we must insert after self
to ensure that the following address will satisfy align
(measured in bytes).
E.g. if self.size is 9, then self.padding_needed_for(4)
returns 3, because that is the minimum number of bytes of
padding required to get a 4-aligned address (assuming that the
corresponding memory block starts at a 4-aligned address).
The return value of this function has no meaning if align is
not a power-of-two.
Note that the utility of the returned value requires align
to be less than or equal to the alignment of the starting
address for the whole allocated block of memory. One way to
satisfy this constraint is to ensure align <= self.align.
Returns a layout padded so the following address be aligned to
align (measured in bytes), assuming the memory block is also
aligned. It is equivalent to appending an array of
self.padding_needed_for(align) bytes.
The return value of this function has no meaning if align is
not a power-of-two.
Note that the utility of the returned value requires align
to be less than or equal to the alignment of the starting
address for the whole allocated block of memory. One way to
satisfy this constraint is to ensure align <= self.align.
Creates a layout describing the record for n instances of
self, with a suitable amount of padding between each to
ensure that each instance is given its requested size and
alignment. On success, returns (k, offs) where k is the
layout of the array and offs is the distance between the start
of each element in the array.
On arithmetic overflow, returns None.
Creates a layout describing the record for self followed by
next, including any necessary padding to ensure that next
will be properly aligned. Note that the result layout will
satisfy the alignment properties of both self and next.
Returns Some((k, offset)), where k is layout of the concatenated
record and offset is the relative location, in bytes, of the
start of the next embedded within the concatenated record
(assuming that the record itself starts at offset 0).
On arithmetic overflow, returns None.
Creates a layout describing the record for n instances of
self, with no padding between each instance.
Note that, unlike repeat, repeat_packed does not guarantee
that the repeated instances of self will be properly
aligned, even if a given instance of self is properly
aligned. In other words, if the layout returned by
repeat_packed is used to allocate an array, it is not
guaranteed that all elements in the array will be properly
aligned.
On arithmetic overflow, returns None.
Creates a layout describing the record for self followed by
next with no additional padding between the two. Since no
padding is inserted, the alignment of next is irrelevant,
and is not incorporated at all into the resulting layout.
Returns (k, offset), where k is layout of the concatenated
record and offset is the relative location, in bytes, of the
start of the next embedded within the concatenated record
(assuming that the record itself starts at offset 0).
(The offset is always the same as self.size(); we use this
signature out of convenience in matching the signature of
extend.)
On arithmetic overflow, returns None.