1 use crate::prelude::*;
2 use serde_derive::{Deserialize, Serialize};
3 
4 /// A map for determining where live GC references live in a stack frame.
5 ///
6 /// Note that this is currently primarily documented as cranelift's
7 /// `binemit::StackMap`, so for detailed documentation about this please read
8 /// the docs over there.
9 #[derive(Debug, Serialize, Deserialize)]
10 pub struct StackMap {
11     bits: Box<[u32]>,
12     mapped_words: u32,
13 }
14 
15 impl StackMap {
16     /// Creates a new `StackMap`, typically from a preexisting
17     /// `binemit::StackMap`.
18     pub fn new(mapped_words: u32, bits: impl Iterator<Item = u32>) -> StackMap {
19         StackMap {
20             bits: bits.collect(),
21             mapped_words,
22         }
23     }
24 
25     /// Returns a specified bit.
26     pub fn get_bit(&self, bit_index: usize) -> bool {
27         assert!(bit_index < 32 * self.bits.len());
28         let word_index = bit_index / 32;
29         let word_offset = bit_index % 32;
30         (self.bits[word_index] & (1 << word_offset)) != 0
31     }
32 
33     /// Returns the number of words represented by this stack map.
34     pub fn mapped_words(&self) -> u32 {
35         self.mapped_words
36     }
37 }
38