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| <h1><a class="header" href="#using-the-bitfield-types-generated-by-bindgen" id="using-the-bitfield-types-generated-by-bindgen">Using the Bitfield Types Generated by Bindgen</a></h1> |
| <h2><a class="header" href="#bitfield-strategy-overview" id="bitfield-strategy-overview">Bitfield Strategy Overview</a></h2> |
| <p>As Rust does not support bitfields, Bindgen generates a struct for each with the following characteristics</p> |
| <ul> |
| <li>Immutable getter functions for each bitfield named <code><bitfield></code></li> |
| <li>Setter functions for each contiguous block of bitfields named <code>set_<bitfield></code></li> |
| <li>For each contiguous block of bitfields, Bindgen emits an opaque physical field that contains one or more logical bitfields</li> |
| <li>A static constructor <code>new_bitfield_{1, 2, ...}</code> with a parameter for each bitfield contained within the opaque physical field.</li> |
| </ul> |
| <h2><a class="header" href="#bitfield-examples" id="bitfield-examples">Bitfield examples</a></h2> |
| <p>For this discussion, we will use the following C type definitions and functions.</p> |
| <pre><code class="language-c">typedef struct { |
| unsigned int a: 1; |
| unsigned int b: 1; |
| unsigned int c: 2; |
| |
| } StructWithBitfields; |
| |
| // Create a default bitfield |
| StructWithBitfields create_bitfield(); |
| |
| // Print a bitfield |
| void print_bitfield(StructWithBitfields bfield); |
| </code></pre> |
| <p>Bindgen creates a set of field getters and setters for interacting with the bitset. For example, </p> |
| <pre><code class="language-rust ignore"> let mut bfield = unsafe { create_bitfield() }; |
| |
| bfield.set_a(1); |
| println!("a set to {}", bfield.a()); |
| bfield.set_b(1); |
| println!("b set to {}", bfield.b()); |
| bfield.set_c(3); |
| println!("c set to {}", bfield.c()); |
| |
| unsafe { print_bitfield(bfield) }; |
| </code></pre> |
| <p>will print out</p> |
| <pre><code class="language-text">a set to 1 |
| b set to 1 |
| c set to 3 |
| StructWithBitfields: a:1, b:1, c:3 |
| </code></pre> |
| <p>Overflowing a bitfield will result in the same behavior as in C/C++: the bitfield will be set to 0.</p> |
| <pre><code class="language-rust ignore"> let mut bfield = unsafe { create_bitfield() }; |
| bfield.set_a(1); |
| bfield.set_b(1); |
| bfield.set_c(12); |
| println!("c set to {} due to overflow", bfield.c()); |
| |
| unsafe { print_bitfield(bfield) }; |
| </code></pre> |
| <p>will print out</p> |
| <pre><code class="language-text">c set to 0 due to overflow |
| StructWithBitfields: a:1, b:1, c:0 |
| </code></pre> |
| <p>To create a new bitfield in Rust, use the bitfield allocation unit constructor.</p> |
| <p>Note: This requires the Builder's derive_default to be set to true, otherwise the necessary Default functions won't be generated.</p> |
| <pre><code class="language-rust ignore"> let bfield = StructWithBitfields{ |
| _bitfield_1: StructWithBitfields::new_bitfield_1(0,0,0), |
| ..Default::default() |
| }; |
| |
| unsafe { print_bitfield(bfield) }; |
| </code></pre> |
| <p>This will print out</p> |
| <pre><code class="language-text">StructWithBitfields: a:0, b:0, c:0 |
| </code></pre> |
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