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# Big-Endian Integer Loading
This method loads an integer value from a bit-slice, using big-endian
significance ordering when the bit-slice spans more than one `T` element in
memory.
Big-endian significance ordering means that if a bit-slice occupies an array
`[A, B, C]`, then the bits stored in `A` are considered to be the most
significant segment of the loaded integer, then `B` contains the middle segment,
then `C` contains the least significant segment.
The segments are combined in order, that is, as the raw bit-pattern
`0b<padding><A><B><C>`. If the destination type is signed, the loaded value is
sign-extended according to the most-significant bit in the `A` segment.
It is important to note that the `O: BitOrder` parameter of the bit-slice from
which the value is loaded **does not** affect the bit-pattern of the stored
segments. They are always stored exactly as they exist in an ordinary integer.
The ordering parameter only affects *which* bits in an element are available for
storage.
## Type Parameters
- `I`: The integer type being loaded. This can be any of the signed or unsigned
integers.
## Parameters
- `&self`: A bit-slice region whose length is in the range `1 ..= I::BITS`.
## Returns
The contents of the bit-slice, interpreted as an integer.
## Panics
This panics if `self.len()` is 0, or greater than `I::BITS`.
## Examples
Let us consider an `i32` value stored in 24 bits of a `BitSlice<u8, Lsb0>`:
```rust
use bitvec::prelude::*;
let mut raw = [0u8; 4];
let bits = raw.view_bits_mut::<Lsb0>();
let integer = 0x00__B4_96_3Cu32 as i32;
bits[4 .. 28].store_be::<i32>(integer);
let loaded = bits[4 .. 28].load_be::<i32>();
assert_eq!(loaded, 0xFF__B4_96_3Cu32 as i32);
```
Observe that, because the lowest 24 bits began with the pattern `0b1101…`, the
value was considered to be negative when interpreted as an `i24` and was
sign-extended through the highest byte.
Let us now look at the memory representation of this value:
```rust
# use bitvec::prelude::*;
# let mut raw = [0u8; 4];
# let bits = raw.view_bits_mut::<Lsb0>();
# bits[4 .. 28].store_be::<u32>(0x00B4963Cu32);
assert_eq!(raw, [
0b1011_0000,
// 0xB dead
0b0100_1001,
// 0x4 0x9
0b0110_0011,
// 0x6 0x3
0b0000_1100,
// dead 0xC
]);
```
Notice how while the `Lsb0` bit-ordering means that indexing within the
bit-slice proceeds right-to-left in each element, the actual bit-patterns stored
in memory are not affected. Element `[0]` is more numerically significant than
element `[1]`, but bit `[4]` is not more numerically significant than bit `[5]`.
In the sequence `B496`, `B` is the most significant, and so it gets placed
lowest in memory. `49` fits in one byte, and is stored directly as written.
Lastly, `6` is the least significant nibble of the four, and is placed highest
in memory.
Now let’s look at the way different `BitOrder` parameters interpret the
placement of bit indices within memory:
```rust
use bitvec::prelude::*;
let raw = [
// Bit index 14 ←
// Lsb0: ─┤
0b0100_0000_0000_0011u16,
// Msb0: ├─
// → 14
// Bit index ← 19 16
// Lsb0: ├──┤
0b0001_0000_0000_1110u16,
// Msb0: ├──┤
// 16 19 →
];
assert_eq!(
raw.view_bits::<Lsb0>()
[14 .. 20]
.load_be::<u8>(),
0b00_01_1110,
);
assert_eq!(
raw.view_bits::<Msb0>()
[14 .. 20]
.load_be::<u8>(),
0b00_11_0001,
);
```
Notice how the bit-orderings change which *parts* of the memory are loaded, but
in both cases the segment in `raw[0]` is more significant than the segment in
`raw[1]`, and the ordering of bits *within* each segment are unaffected by the
bit-ordering.
## Notes
Be sure to see the documentation for
[`<BitSlice<_, Lsb0> as BitField>::load_be`][llb] and
[`<BitSlice<_, Msb0> as Bitfield>::load_be`][mlb] for more detailed information
on the memory views!
You can view the mask of all *storage regions* of a bit-slice by using its
[`.domain()`] method to view the breakdown of its memory region, then print the
[`.mask()`] of any [`PartialElement`] the domain contains. Whole elements are
always used in their entirety. You should use the `domain` module’s types
whenever you are uncertain of the exact locations in memory that a particular
bit-slice governs.
[llb]: https://docs.rs/bitvec/latest/bitvec/field/trait.BitField.html#method.load_be-3
[mlb]: https://docs.rs/bitvec/latest/bitvec/field/trait.BitField.html#method.load_be-4
[`PartialElement`]: crate::domain::PartialElement
[`.domain()`]: crate::slice::BitSlice::domain
[`.mask()`]: crate::domain::PartialElement::mask
|
