tiny.reducer.Capacity

1/// Workspace layout derived from the caller's limits, sized so that a run in2/// steady state needs no further allocation.3pub const Capacity = struct {4    /// Caller's limits that this capacity was derived from.5    limits: Limits,6    /// Byte offset in the backing allocation where the scratch lane starts. It7    /// equals `limits.max_input_bytes` exactly.8    candidate_offset: usize,9    /// Greatest length in bytes any candidate takes, which is $\max(N - 1, 0)$.10    candidate_bytes: usize,11    /// Total the combined allocation needs, which is12    /// $\text{candidate\_offset} + \text{candidate\_bytes}$.13    storage_bytes: usize,1415    /// Works out the memory a workspace needs to reduce inputs up to16    /// `limits.max_input_bytes`. It computes $N + \max(N - 1, 0)$, taking the17    /// scratch lane's length with saturating subtraction and the total with18    /// checked addition. It produces the arithmetic layout alone and calls no19    /// allocator.20    ///21    /// ## Errors22    /// It returns `DeriveError.CapacityOverflow` when the combined requirement23    /// exceeds `std.math.maxInt(usize)`.24    pub fn derive(limits: Limits) DeriveError!Capacity {25        const candidate_bytes = limits.max_input_bytes -| 1;26        const capacity = Capacity{27            .limits = limits,28            .candidate_offset = limits.max_input_bytes,29            .candidate_bytes = candidate_bytes,30            .storage_bytes = std.math.add(31                usize,32                limits.max_input_bytes,33                candidate_bytes,34            ) catch return error.CapacityOverflow,35        };36        std.debug.assert(capacity.candidate_offset == limits.max_input_bytes);37        std.debug.assert(capacity.candidate_bytes <= limits.max_input_bytes);38        std.debug.assert(capacity.storage_bytes >= limits.max_input_bytes);39        std.debug.assert(40            capacity.candidate_offset + capacity.candidate_bytes == capacity.storage_bytes,41        );42        return capacity;43    }44};

1/// Workspace layout derived from the caller's limits, sized so that a run in2/// steady state needs no further allocation.3pub const Capacity = bytes.Capacity;