pipecircuit 0.0.11

Correct. Robust. Fast. Portable.
Documentation 
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
141
142
143

use alloc::vec::Vec;

use super::{SlotLocation, StableSlot, StableSlots, StableSlotsInconsistency};

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum StableSlotInsertError {
    Full { maximum_rows: usize },
    Inconsistent { reason: StableSlotsInconsistency },
}

impl StableSlots {
    pub fn try_prepare_insert(
        &mut self,
    ) -> Result<PreparedStableSlotInsert<'_>, StableSlotInsertError> {
        let Self {
            maximum_rows,
            row_to_slot,
            slot_locations,
            first_free,
        } = self;
        if row_to_slot.len() >= *maximum_rows {
            return Err(StableSlotInsertError::Full {
                maximum_rows: *maximum_rows,
            });
        }
        let row =
            u32::try_from(row_to_slot.len()).map_err(|_| StableSlotInsertError::Inconsistent {
                reason: StableSlotsInconsistency::RowUnrepresentable {
                    row: row_to_slot.len(),
                },
            })?;
        let insertion = match *first_free {
            Some(slot) => prepare_reuse(slot_locations, first_free, slot)?,
            None => prepare_new(slot_locations)?,
        };
        let slot = insertion.slot();
        Ok(PreparedStableSlotInsert {
            row_to_slot,
            insertion,
            slot,
            row,
        })
    }
}

fn prepare_reuse<'slots>(
    slot_locations: &'slots mut [SlotLocation],
    first_free: &'slots mut Option<StableSlot>,
    slot: StableSlot,
) -> Result<StableSlotInsertion<'slots>, StableSlotInsertError> {
    let slot_index =
        usize::try_from(slot.value()).map_err(|_| StableSlotInsertError::Inconsistent {
            reason: StableSlotsInconsistency::SlotUnrepresentable { slot },
        })?;
    let location =
        slot_locations
            .get_mut(slot_index)
            .ok_or(StableSlotInsertError::Inconsistent {
                reason: StableSlotsInconsistency::SlotUnavailable { slot },
            })?;
    let next_free = match location {
        SlotLocation::Free(next_free) => *next_free,
        SlotLocation::Occupied(row) => {
            return Err(StableSlotInsertError::Inconsistent {
                reason: StableSlotsInconsistency::SlotOccupied { slot, row: *row },
            });
        }
    };
    Ok(StableSlotInsertion::Reused {
        location,
        first_free,
        next_free,
        slot,
    })
}

fn prepare_new(
    slot_locations: &mut Vec<SlotLocation>,
) -> Result<StableSlotInsertion<'_>, StableSlotInsertError> {
    let slot_value =
        u32::try_from(slot_locations.len()).map_err(|_| StableSlotInsertError::Inconsistent {
            reason: StableSlotsInconsistency::NewSlotUnrepresentable {
                slot: slot_locations.len(),
            },
        })?;
    Ok(StableSlotInsertion::New {
        slot_locations,
        slot: StableSlot::new(slot_value),
    })
}

enum StableSlotInsertion<'slots> {
    New {
        slot_locations: &'slots mut Vec<SlotLocation>,
        slot: StableSlot,
    },
    Reused {
        location: &'slots mut SlotLocation,
        first_free: &'slots mut Option<StableSlot>,
        next_free: Option<StableSlot>,
        slot: StableSlot,
    },
}

impl StableSlotInsertion<'_> {
    const fn slot(&self) -> StableSlot {
        match self {
            Self::New { slot, .. } | Self::Reused { slot, .. } => *slot,
        }
    }
}

pub struct PreparedStableSlotInsert<'slots> {
    row_to_slot: &'slots mut Vec<StableSlot>,
    insertion: StableSlotInsertion<'slots>,
    slot: StableSlot,
    row: u32,
}

impl PreparedStableSlotInsert<'_> {
    pub const fn slot(&self) -> StableSlot {
        self.slot
    }

    pub fn commit(self) -> StableSlot {
        match self.insertion {
            StableSlotInsertion::New { slot_locations, .. } => {
                slot_locations.push(SlotLocation::Occupied(self.row));
            }
            StableSlotInsertion::Reused {
                location,
                first_free,
                next_free,
                ..
            } => {
                *location = SlotLocation::Occupied(self.row);
                *first_free = next_free;
            }
        }
        self.row_to_slot.push(self.slot);
        self.slot
    }
}