qubit-io 0.8.0

Byte-stream buffering and std::io utilities for Rust
Documentation 
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// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================

use std::io::{
    Read,
    Result,
};

/// Minimal indexed input interface over units.
///
/// `Input` is intentionally smaller and lower-level than [`Read`]. It only
/// states that an implementor can read up to `count` units into
/// `output[index..index + count]`. The caller owns range validation so hot
/// paths can avoid repeated slicing and bounds checks.
pub trait Input {
    /// The unit type read from this input.
    type Item;

    /// Reads units into an indexed output range without checking the range.
    ///
    /// # Parameters
    ///
    /// * `output` - Destination storage.
    /// * `index` - Start index inside `output`.
    /// * `count` - Maximum number of units to read.
    ///
    /// # Returns
    ///
    /// The number of units written into `output[index..index + count]`. The
    /// value must be in `0..=count`.
    ///
    /// # Errors
    ///
    /// Returns the input error reported by the implementation.
    ///
    /// # Safety
    ///
    /// The caller must guarantee that `index..index + count` is a valid range
    /// inside `output` and that the addition does not overflow.
    unsafe fn read_unchecked(
        &mut self,
        output: &mut [Self::Item],
        index: usize,
        count: usize,
    ) -> Result<usize>;
}

impl<R> Input for R
where
    R: Read + ?Sized,
{
    type Item = u8;

    /// Reads bytes from a standard [`Read`] value into an indexed range.
    #[inline(always)]
    unsafe fn read_unchecked(
        &mut self,
        output: &mut [u8],
        index: usize,
        count: usize,
    ) -> Result<usize> {
        debug_assert!(
            index
                .checked_add(count)
                .is_some_and(|end| end <= output.len()),
            "unchecked read range exceeds output buffer"
        );
        // SAFETY: The caller guarantees that the range is valid inside
        // `output`.
        let target = unsafe {
            core::slice::from_raw_parts_mut(
                output.as_mut_ptr().add(index),
                count,
            )
        };
        self.read(target)
    }
}