error[E0658]: use of unstable library feature `maybe_uninit_slice`
       --> src/lib.rs:227:47
        |
    227 |     unsafe { str::from_utf8_unchecked(written.assume_init_ref()) }
        |                                               ^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:254:30
        |
    254 |                     unsafe { core::hint::assert_unchecked(offset >= 4) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:257:30
        |
    257 |                     unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:278:30
        |
    278 |                     unsafe { core::hint::assert_unchecked(offset >= 2) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:281:30
        |
    281 |                     unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:294:30
        |
    294 |                     unsafe { core::hint::assert_unchecked(offset >= 1) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:297:30
        |
    297 |                     unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...
    313 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:352:22
        |
    352 |             unsafe { core::hint::assert_unchecked(offset >= 4) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:355:22
        |
    355 |             unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:373:22
        |
    373 |             unsafe { core::hint::assert_unchecked(offset >= 2) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:376:22
        |
    376 |             unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:389:22
        |
    389 |             unsafe { core::hint::assert_unchecked(offset >= 1) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0658]: use of unstable library feature 'hint_assert_unchecked'
       --> src/lib.rs:392:22
        |
    392 |             unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
        |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    error[E0425]: cannot find function `size_of` in this scope
       --> src/lib.rs:246:23
        |
    246 |                 while size_of::<Self>() > 1
        |                       ^^^^^^^ not found in this scope
    ...
    325 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = note: this error originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: consider importing this function
        |
    45  + use core::mem::size_of;
        |

    error[E0658]: use of unstable library feature 'slice_first_last_chunk'
       --> src/lib.rs:160:46
        |
    160 |                 let (prefix, unsigned) = buf.split_last_chunk_mut().unwrap();
        |                                              ^^^^^^^^^^^^^^^^^^^^
    ...
    173 | impl_Integer!(i8, u8);
        | --------------------- in this macro invocation
        |
        = note: see issue #111774 <rust-lang/rust#111774> for more information
        = note: this error originates in the macro `impl_Integer` (in Nightly builds, run with -Z macro-backtrace for more info)

    error[E0308]: mismatched types
       --> src/lib.rs:161:84
        |
    161 |                 let mut offset = prefix.len() + Unsigned::fmt(self.unsigned_abs(), unsigned);
        |                                                 -------------                      ^^^^^^^^ expected `&mut [MaybeUninit<u8>; 3]`, found `&mut [MaybeUninit<u8>]`
        |                                                 |
        |                                                 arguments to this function are incorrect
    ...
    173 | impl_Integer!(i8, u8);
        | --------------------- in this macro invocation
        |
        = note: expected mutable reference `&mut [MaybeUninit<u8>; 3]`
                   found mutable reference `&mut [MaybeUninit<u8>]`
    note: method defined here
       --> src/lib.rs:231:8
        |
    231 |     fn fmt(self, buf: &mut Self::Buffer) -> usize;
        |        ^^^
        = note: this error originates in the macro `impl_Integer` (in Nightly builds, run with -Z macro-backtrace for more info)

    warning: this operation has no effect
       --> src/lib.rs:382:17
        |
    382 |             buf[offset + 0].write(DECIMAL_PAIRS[pair1 * 2 + 0]);
        |                 ^^^^^^^^^^ help: consider reducing it to: `offset`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op
        = note: `-W clippy::identity-op` implied by `-W clippy::all`
        = help: to override `-W clippy::all` add `#[allow(clippy::identity_op)]`

    warning: this operation has no effect
       --> src/lib.rs:382:49
        |
    382 |             buf[offset + 0].write(DECIMAL_PAIRS[pair1 * 2 + 0]);
        |                                                 ^^^^^^^^^^^^^ help: consider reducing it to: `(pair1 * 2)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:384:49
        |
    384 |             buf[offset + 2].write(DECIMAL_PAIRS[pair2 * 2 + 0]);
        |                                                 ^^^^^^^^^^^^^ help: consider reducing it to: `(pair2 * 2)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:404:17
        |
    404 |             buf[offset + 0].write(DECIMAL_PAIRS[pair * 2 + 0]);
        |                 ^^^^^^^^^^ help: consider reducing it to: `offset`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:404:49
        |
    404 |             buf[offset + 0].write(DECIMAL_PAIRS[pair * 2 + 0]);
        |                                                 ^^^^^^^^^^^^ help: consider reducing it to: `(pair * 2)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:445:13
        |
    445 |         buf[quad_index * 4 + OFFSET + 0].write(DECIMAL_PAIRS[pair1 * 2 + 0]);
        |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider reducing it to: `(quad_index * 4 + OFFSET)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:445:62
        |
    445 |         buf[quad_index * 4 + OFFSET + 0].write(DECIMAL_PAIRS[pair1 * 2 + 0]);
        |                                                              ^^^^^^^^^^^^^ help: consider reducing it to: `(pair1 * 2)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: this operation has no effect
       --> src/lib.rs:447:62
        |
    447 |         buf[quad_index * 4 + OFFSET + 2].write(DECIMAL_PAIRS[pair2 * 2 + 0]);
        |                                                              ^^^^^^^^^^^^^ help: consider reducing it to: `(pair2 * 2)`
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

    warning: adding items after statements is confusing, since items exist from the start of the scope
       --> src/lib.rs:472:5
        |
    472 |     const M_HIGH: u128 = 76624777043294442917917351357515459181;
        |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements
        = note: `-W clippy::items-after-statements` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::items_after_statements)]`

    warning: adding items after statements is confusing, since items exist from the start of the scope
       --> src/lib.rs:473:5
        |
    473 |     const SH_POST: u8 = 51;
        |     ^^^^^^^^^^^^^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements

On my machine, benchmarks are 15% faster without these...

    warning: casts from `u8` to `u32` can be expressed infallibly using `From`
       --> src/lib.rs:278:52
        |
    278 |                     let (pair1, pair2) = divmod100(quad as u32);
        |                                                    ^^^^^^^^^^^
    ...
    322 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
        = note: `-W clippy::cast-lossless` implied by `-W clippy::pedantic`
        = help: to override `-W clippy::pedantic` add `#[allow(clippy::cast_lossless)]`
        = note: this warning originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: use `u32::from` instead
        |
    278 -                     let (pair1, pair2) = divmod100(quad as u32);
    278 +                     let (pair1, pair2) = divmod100(u32::from(quad));
        |

        Checking itertools v0.13.0
    warning: casts from `u8` to `u32` can be expressed infallibly using `From`
       --> src/lib.rs:295:50
        |
    295 |                     let (last, pair) = divmod100(remain as u32);
        |                                                  ^^^^^^^^^^^^^
    ...
    322 | impl_Unsigned!(u8);
        | ------------------ in this macro invocation
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
        = note: this warning originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: use `u32::from` instead
        |
    295 -                     let (last, pair) = divmod100(remain as u32);
    295 +                     let (last, pair) = divmod100(u32::from(remain));
        |

    warning: casts from `u16` to `u32` can be expressed infallibly using `From`
       --> src/lib.rs:278:52
        |
    278 |                     let (pair1, pair2) = divmod100(quad as u32);
        |                                                    ^^^^^^^^^^^
    ...
    323 | impl_Unsigned!(u16);
        | ------------------- in this macro invocation
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
        = note: this warning originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: use `u32::from` instead
        |
    278 -                     let (pair1, pair2) = divmod100(quad as u32);
    278 +                     let (pair1, pair2) = divmod100(u32::from(quad));
        |

    warning: casts from `u16` to `u32` can be expressed infallibly using `From`
       --> src/lib.rs:295:50
        |
    295 |                     let (last, pair) = divmod100(remain as u32);
        |                                                  ^^^^^^^^^^^^^
    ...
    323 | impl_Unsigned!(u16);
        | ------------------- in this macro invocation
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
        = note: this warning originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: use `u32::from` instead
        |
    295 -                     let (last, pair) = divmod100(remain as u32);
    295 +                     let (last, pair) = divmod100(u32::from(remain));
        |

    warning: casts from `u32` to `u64` can be expressed infallibly using `From`
       --> src/lib.rs:296:30
        |
    296 |                     remain = last as Self;
        |                              ^^^^^^^^^^^^
    ...
    325 | impl_Unsigned!(u64);
        | ------------------- in this macro invocation
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
        = note: this warning originates in the macro `impl_Unsigned` (in Nightly builds, run with -Z macro-backtrace for more info)
    help: use `Self::from` instead
        |
    296 -                     remain = last as Self;
    296 +                     remain = Self::from(last);
        |

    warning: casts from `u32` to `u64` can be expressed infallibly using `From`
       --> src/lib.rs:378:22
        |
    378 |             remain = last as u64;
        |                      ^^^^^^^^^^^
        |
        = help: an `as` cast can become silently lossy if the types change in the future
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cast_lossless
    help: use `u64::from` instead
        |
    378 -             remain = last as u64;
    378 +             remain = u64::from(last);
        |