1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

use crate::{BddPartialValuation, BddVariable};
use std::convert::TryFrom;

impl BddPartialValuation {
    /// Creates an empty valuation without any variables set.
    pub fn empty() -> BddPartialValuation {
        BddPartialValuation(Vec::new())
    }

    /// True if the valuation contains no values.
    pub fn is_empty(&self) -> bool {
        self.0.iter().all(|it| it.is_none())
    }

    /// Return the number of fixed variables in this valuation.
    pub fn cardinality(&self) -> u16 {
        u16::try_from(self.0.iter().filter(|it| it.is_some()).count()).unwrap()
    }

    /// Return the identifier of the last fixed variable in this valuation. Returns `None` if
    /// no variable is fixed.
    pub fn last_fixed_variable(&self) -> Option<BddVariable> {
        for i in (0..self.0.len()).rev() {
            if self.0[i].is_some() {
                return Some(BddVariable(i as u16));
            }
        }
        None
    }

    /// Create a partial valuation from a list of variables and values.
    ///
    /// The order of variables in the slice can be arbitrary. The operation does not perform
    /// any uniqueness checking. If the slice contains multiple copies of the same variable,
    /// the last value is accepted.
    pub fn from_values(values: &[(BddVariable, bool)]) -> BddPartialValuation {
        let mut result = Self::empty();
        for (id, value) in values {
            result.set_value(*id, *value)
        }
        result
    }

    /// Consume this valuation and turn it into a vector of values which are stored in it.
    pub fn to_values(&self) -> Vec<(BddVariable, bool)> {
        self.0
            .iter()
            .enumerate()
            .filter_map(|(i, value)| value.map(|value| (BddVariable(i as u16), value)))
            .collect()
    }

    /// Get a value stored for the given variable id, if any.
    pub fn get_value(&self, id: BddVariable) -> Option<bool> {
        let index = usize::from(id.0);
        self.0.get(index).cloned().flatten()
    }

    /// Returns `true` if this valuation has the value of `id` variable set.
    pub fn has_value(&self, id: BddVariable) -> bool {
        self.get_value(id).is_some()
    }

    /// Update value of the given `id` variable.
    pub fn set_value(&mut self, id: BddVariable, value: bool) {
        let cell = self.mut_cell(id);
        *cell = Some(value);
    }

    /// Remove value of a variable from this valuation.
    ///
    /// If the value was not set, this operation has no effect.
    pub fn unset_value(&mut self, id: BddVariable) {
        let cell = self.mut_cell(id);
        *cell = None;
    }

    fn mut_cell(&mut self, id: BddVariable) -> &mut Option<bool> {
        let index = usize::from(id.0);
        while self.0.len() <= index {
            self.0.push(None);
        }
        &mut self.0[index]
    }

    /// Returns true if the values set in this partial valuation match the values fixed in the
    /// other given valuation. I.e. the two valuations agree on fixed values in `valuation`.
    ///
    /// In other words `this >= valuation` in terms of specificity.
    pub fn extends(&self, valuation: &BddPartialValuation) -> bool {
        for var_id in 0..(valuation.0.len() as u16) {
            let var = BddVariable(var_id);
            let expected = valuation.get_value(var);
            if expected.is_some() && self.get_value(var) != expected {
                return false;
            }
        }

        true
    }
}

impl Default for BddPartialValuation {
    fn default() -> Self {
        Self::empty()
    }
}

#[cfg(test)]
mod tests {
    use crate::{BddPartialValuation, BddVariable};

    #[test]
    fn basic_partial_valuation_properties() {
        let v1 = BddVariable(1);
        let v2 = BddVariable(2);
        let v5 = BddVariable(5);

        let mut a = BddPartialValuation::default();
        assert!(a.last_fixed_variable().is_none());
        assert!(!a.has_value(v1));
        a.set_value(v1, true);
        assert!(a.has_value(v1));
        assert_eq!(Some(true), a.get_value(v1));
        a.set_value(v2, false);
        a.unset_value(v1);
        assert!(a.has_value(v2));
        assert!(!a.has_value(v1));

        a.set_value(v5, true);
        assert_eq!(Some(v5), a.last_fixed_variable());
        a.set_value(v1, false);
        assert_eq!(3, a.cardinality());

        let b = BddPartialValuation::from_values(&[(v1, false), (v5, true), (v2, false)]);

        assert_eq!(a, b);
        assert_eq!(a, BddPartialValuation::from_values(&a.to_values()));
    }
}