    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
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290

    //! [![github]](https://github.com/dtolnay/itoa)&ensp;[![crates-io]](https://crates.io/crates/itoa)&ensp;[![docs-rs]](https://docs.rs/itoa)
    //!
    //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
    //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
    //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
    //!
    //! <br>
    //!
    //! This crate provides a fast conversion of integer primitives to decimal
    //! strings. The implementation comes straight from [libcore] but avoids the
    //! performance penalty of going through [`core::fmt::Formatter`].
    //!
    //! See also [`ryu`] for printing floating point primitives.
    //!
    //! [libcore]: https://github.com/rust-lang/rust/blob/b8214dc6c6fc20d0a660fb5700dca9ebf51ebe89/src/libcore/fmt/num.rs#L201-L254
    //! [`core::fmt::Formatter`]: https://doc.rust-lang.org/std/fmt/struct.Formatter.html
    //! [`ryu`]: https://github.com/dtolnay/ryu
    //!
    //! # Example
    //!
    //! ```
    //! fn main() {
    //!     let mut buffer = itoa::Buffer::new();
    //!     let printed = buffer.format(128u64);
    //!     assert_eq!(printed, "128");
    //! }
    //! ```
    //!
    //! # Performance (lower is better)
    //!
    //! ![performance](https://raw.githubusercontent.com/dtolnay/itoa/master/performance.png)

    #![doc(html_root_url = "https://docs.rs/itoa/1.0.5")]
    #![no_std]
    #![allow(
        clippy::cast_lossless,
        clippy::cast_possible_truncation,
        clippy::must_use_candidate,
        clippy::unreadable_literal
    )]

    mod udiv128;

    use core::mem::{self, MaybeUninit};
    use core::{ptr, slice, str};
    #[cfg(feature = "no-panic")]
    use no_panic::no_panic;

    /// A correctly sized stack allocation for the formatted integer to be written
    /// into.
    ///
    /// # Example
    ///
    /// ```
    /// let mut buffer = itoa::Buffer::new();
    /// let printed = buffer.format(1234);
    /// assert_eq!(printed, "1234");
    /// ```
    pub struct Buffer {
        bytes: [MaybeUninit<u8>; I128_MAX_LEN],
    }

    impl Default for Buffer {
        #[inline]
        fn default() -> Buffer {
            Buffer::new()
        }
    }

    impl Clone for Buffer {
        #[inline]
        fn clone(&self) -> Self {
            Buffer::new()
        }
    }

    impl Buffer {
        /// This is a cheap operation; you don't need to worry about reusing buffers
        /// for efficiency.
        #[inline]
        #[cfg_attr(feature = "no-panic", no_panic)]
        pub fn new() -> Buffer {
            let bytes = [MaybeUninit::<u8>::uninit(); I128_MAX_LEN];
            Buffer { bytes }
        }

        /// Print an integer into this buffer and return a reference to its string
        /// representation within the buffer.
        #[cfg_attr(feature = "no-panic", no_panic)]
        pub fn format<I: Integer>(&mut self, i: I) -> &str {
            i.write(unsafe {
                &mut *(&mut self.bytes as *mut [MaybeUninit<u8>; I128_MAX_LEN]
                    as *mut <I as private::Sealed>::Buffer)
            })
        }
    }

    /// An integer that can be written into an [`itoa::Buffer`][Buffer].
    ///
    /// This trait is sealed and cannot be implemented for types outside of itoa.
    pub trait Integer: private::Sealed {}

    // Seal to prevent downstream implementations of the Integer trait.
    mod private {
        pub trait Sealed: Copy {
            type Buffer: 'static;
            fn write(self, buf: &mut Self::Buffer) -> &str;
        }
    }

    const DEC_DIGITS_LUT: &[u8] = b"\
          0001020304050607080910111213141516171819\
          2021222324252627282930313233343536373839\
          4041424344454647484950515253545556575859\
          6061626364656667686970717273747576777879\
          8081828384858687888990919293949596979899";

    // Adaptation of the original implementation at
    // https://github.com/rust-lang/rust/blob/b8214dc6c6fc20d0a660fb5700dca9ebf51ebe89/src/libcore/fmt/num.rs#L188-L266
    macro_rules! impl_Integer {
        ($($max_len:expr => $t:ident),* as $conv_fn:ident) => {$(
            impl Integer for $t {}

            impl private::Sealed for $t {
                type Buffer = [MaybeUninit<u8>; $max_len];

                #[allow(unused_comparisons)]
                #[inline]
                #[cfg_attr(feature = "no-panic", no_panic)]
                fn write(self, buf: &mut [MaybeUninit<u8>; $max_len]) -> &str {
                    let is_nonnegative = self >= 0;
                    let mut n = if is_nonnegative {
                        self as $conv_fn
                    } else {
                        // convert the negative num to positive by summing 1 to it's 2 complement
                        (!(self as $conv_fn)).wrapping_add(1)
                    };
                    let mut curr = buf.len() as isize;
                    let buf_ptr = buf.as_mut_ptr() as *mut u8;
                    let lut_ptr = DEC_DIGITS_LUT.as_ptr();

                    unsafe {
                        // need at least 16 bits for the 4-characters-at-a-time to work.
                        if mem::size_of::<$t>() >= 2 {
                            // eagerly decode 4 characters at a time
                            while n >= 10000 {
                                let rem = (n % 10000) as isize;
                                n /= 10000;

                                let d1 = (rem / 100) << 1;
                                let d2 = (rem % 100) << 1;
                                curr -= 4;
                                ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                                ptr::copy_nonoverlapping(lut_ptr.offset(d2), buf_ptr.offset(curr + 2), 2);
                            }
                        }

                        // if we reach here numbers are <= 9999, so at most 4 chars long
                        let mut n = n as isize; // possibly reduce 64bit math

                        // decode 2 more chars, if > 2 chars
                        if n >= 100 {
                            let d1 = (n % 100) << 1;
                            n /= 100;
                            curr -= 2;
                            ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                        }

                        // decode last 1 or 2 chars
                        if n < 10 {
                            curr -= 1;
                            *buf_ptr.offset(curr) = (n as u8) + b'0';
                        } else {
                            let d1 = n << 1;
                            curr -= 2;
                            ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                        }

                        if !is_nonnegative {
                            curr -= 1;
                            *buf_ptr.offset(curr) = b'-';
                        }
                    }

                    let len = buf.len() - curr as usize;
                    let bytes = unsafe { slice::from_raw_parts(buf_ptr.offset(curr), len) };
                    unsafe { str::from_utf8_unchecked(bytes) }
                }
            }
        )*};
    }

    const I8_MAX_LEN: usize = 4;
    const U8_MAX_LEN: usize = 3;
    const I16_MAX_LEN: usize = 6;
    const U16_MAX_LEN: usize = 5;
    const I32_MAX_LEN: usize = 11;
    const U32_MAX_LEN: usize = 10;
    const I64_MAX_LEN: usize = 20;
    const U64_MAX_LEN: usize = 20;

    impl_Integer!(
        I8_MAX_LEN => i8,
        U8_MAX_LEN => u8,
        I16_MAX_LEN => i16,
        U16_MAX_LEN => u16,
        I32_MAX_LEN => i32,
        U32_MAX_LEN => u32
        as u32);

    impl_Integer!(I64_MAX_LEN => i64, U64_MAX_LEN => u64 as u64);

    #[cfg(target_pointer_width = "16")]
    impl_Integer!(I16_MAX_LEN => isize, U16_MAX_LEN => usize as u16);

    #[cfg(target_pointer_width = "32")]
    impl_Integer!(I32_MAX_LEN => isize, U32_MAX_LEN => usize as u32);

    #[cfg(target_pointer_width = "64")]
    impl_Integer!(I64_MAX_LEN => isize, U64_MAX_LEN => usize as u64);

    macro_rules! impl_Integer128 {
        ($($max_len:expr => $t:ident),*) => {$(
            impl Integer for $t {}

            impl private::Sealed for $t {
                type Buffer = [MaybeUninit<u8>; $max_len];

                #[allow(unused_comparisons)]
                #[inline]
                #[cfg_attr(feature = "no-panic", no_panic)]
                fn write(self, buf: &mut [MaybeUninit<u8>; $max_len]) -> &str {
                    let is_nonnegative = self >= 0;
                    let n = if is_nonnegative {
                        self as u128
                    } else {
                        // convert the negative num to positive by summing 1 to it's 2 complement
                        (!(self as u128)).wrapping_add(1)
                    };
                    let mut curr = buf.len() as isize;
                    let buf_ptr = buf.as_mut_ptr() as *mut u8;

                    unsafe {
                        // Divide by 10^19 which is the highest power less than 2^64.
                        let (n, rem) = udiv128::udivmod_1e19(n);
                        let buf1 = buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN];
                        curr -= rem.write(&mut *buf1).len() as isize;

                        if n != 0 {
                            // Memset the base10 leading zeros of rem.
                            let target = buf.len() as isize - 19;
                            ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
                            curr = target;

                            // Divide by 10^19 again.
                            let (n, rem) = udiv128::udivmod_1e19(n);
                            let buf2 = buf_ptr.offset(curr - U64_MAX_LEN as isize) as *mut [MaybeUninit<u8>; U64_MAX_LEN];
                            curr -= rem.write(&mut *buf2).len() as isize;

                            if n != 0 {
                                // Memset the leading zeros.
                                let target = buf.len() as isize - 38;
                                ptr::write_bytes(buf_ptr.offset(target), b'0', (curr - target) as usize);
                                curr = target;

                                // There is at most one digit left
                                // because u128::max / 10^19 / 10^19 is 3.
                                curr -= 1;
                                *buf_ptr.offset(curr) = (n as u8) + b'0';
                            }
                        }

                        if !is_nonnegative {
                            curr -= 1;
                            *buf_ptr.offset(curr) = b'-';
                        }

                        let len = buf.len() - curr as usize;
                        let bytes = slice::from_raw_parts(buf_ptr.offset(curr), len);
                        str::from_utf8_unchecked(bytes)
                    }
                }
            }
        )*};
    }

    const U128_MAX_LEN: usize = 39;
    const I128_MAX_LEN: usize = 40;

    impl_Integer128!(I128_MAX_LEN => i128, U128_MAX_LEN => u128);