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    // This is a modified version of the `itoa` crate by David Tolnay:
    // https://github.com/dtolnay/itoa
    //
    // The crate itself borrows code from the stdlib of Rust.
    //
    // The algorithm here was modified from being able to just writing integers,
    // to printing decimal floating points.

    use std::{io, mem, ptr, slice};

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

    const ZEROFILL: &'static [u8] = &[b'0'; 20];

    #[inline(always)]
    unsafe fn write_num(n: &mut u64, curr: &mut isize, buf_ptr: *mut u8, lut_ptr: *const u8) {
        // eagerly decode 4 digits 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);
        }

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

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

    pub unsafe fn write<W: io::Write>(wr: &mut W, positive: bool, mut n: u64, exponent: i16) -> io::Result<()> {
        if !positive {
            wr.write_all(b"-")?;
        }

        if n == 0 {
            return wr.write_all(b"0");
        }

        const BUF_LEN: usize = 30;
        let mut buf = mem::MaybeUninit::<[u8; BUF_LEN]>::uninit();
        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();

        if exponent == 0 {
            write_num(&mut n, &mut curr, buf_ptr, lut_ptr);

            return wr.write_all(
                slice::from_raw_parts(
                    buf_ptr.offset(curr),
                    BUF_LEN - curr as usize
                )
            );
        } else if exponent < 0 {
            let mut e = safe_abs(exponent);

            // Decimal number with a fraction that's fully printable
            if e < 18 {
                // eagerly decode 4 digits at a time
                for _ in 0 .. e >> 2 {
                    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);
                }

                e &= 3;

                // write the remaining 3, 2 or 1 digits
                if e & 2 == 2 {
                    let d1 = ((n % 100) << 1) as isize;
                    n /= 100;
                    curr -= 2;
                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                }

                if e & 1 == 1 {
                    curr -= 1;
                    *buf_ptr.offset(curr) = ((n % 10) as u8) + b'0';
                    n /= 10;
                }

                curr -= 1;
                *buf_ptr.offset(curr) = b'.';

                write_num(&mut n, &mut curr, buf_ptr, lut_ptr);

                return wr.write_all(
                    slice::from_raw_parts(buf_ptr.offset(curr), BUF_LEN - curr as usize)
                );
            }

            // Not easily printable, write down fraction, then full number, then exponent

            // Since we move the decimal point right after the first digit, we have to adjust the
            // exponent part. If the number is long enough, this may result in the exponent switching
            // sign from negative to positive - we have to handle this case separately.
            let mut exponent_positive = false;
            if n < 10 {
                // Single digit, no fraction
                curr -= 1;
                *buf_ptr.offset(curr) = ((n % 10) as u8) + b'0';
            } else {
                // eagerly decode 4 digits at a time
                while n >= 100000 {
                    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);
                }

                // decode 2 more digits
                if n >= 1000 {
                    let d1 = ((n % 100) << 1) as isize;
                    n /= 100;
                    curr -= 2;
                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                }

                // decode last 1 or 2 digits
                if n < 100 {
                    curr -= 1;
                    *buf_ptr.offset(curr) = ((n % 10) as u8) + b'0';
                    n /= 10;
                } else {
                    let d1 = ((n % 100) << 1) as isize;
                    n /= 100;
                    curr -= 2;
                    ptr::copy_nonoverlapping(lut_ptr.offset(d1), buf_ptr.offset(curr), 2);
                }

                let printed_so_far = BUF_LEN as u16 - curr as u16;

                if printed_so_far <= e {
                    // Subtract the amount of digits printed in the fraction
                    // from the exponent that we still need to print using
                    // the `e` notation
                    e -= printed_so_far;
                } else {
                    // Same as e = |e - printed_so_far|.
                    e = printed_so_far - e;
                    exponent_positive = true;
                }

                curr -= 1;
                *buf_ptr.offset(curr) = b'.';

                write_num(&mut n, &mut curr, buf_ptr, lut_ptr);
            }

            // Write out the number with a fraction
            wr.write_all(
                slice::from_raw_parts(
                    buf_ptr.offset(curr),
                    BUF_LEN - curr as usize
                )
            )?;

            // Omit the 'e' notation for e == 0
            if e == 0 {
                return Ok(());
            }
            // Write the remaining `e` notation, with proper sign
            if exponent_positive {
                wr.write_all(b"e+")?;
            } else {
                wr.write_all(b"e-")?;
            }
            return write(wr, true, e as u64, 0);

        }

        // Exponent greater than 0
        write_num(&mut n, &mut curr, buf_ptr, lut_ptr);
        let printed = BUF_LEN - curr as usize;

        // No need for `e` notation, just print out zeroes
        if (printed + exponent as usize) <= 20 {
            wr.write_all(
                slice::from_raw_parts(
                    buf_ptr.offset(curr),
                    BUF_LEN - curr as usize
                )
            )?;

            return wr.write_all(&ZEROFILL[ .. exponent as usize]);
        }

        let mut e = exponent as u64;

        // More than one digit, turn into a fraction
        if printed != 1 {
            *buf_ptr.offset(curr - 1) = *buf_ptr.offset(curr);
            *buf_ptr.offset(curr) = b'.';
            curr -= 1;
            e += (printed as u64) - 1;
        }

        wr.write_all(
            slice::from_raw_parts(
                buf_ptr.offset(curr),
                BUF_LEN - curr as usize
            )
        )?;
        wr.write_all(b"e")?;
        write(wr, true, e, 0)
    }

    fn safe_abs(x : i16) -> u16 {
        if let Some(y) = x.checked_abs() {
            y as u16
        } else {
            i16::max_value() as u16 + 1u16
        }
    }