ftoa 0.1.1

// Copyright 2016 Dtoa Developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

const MAX_DECIMAL_PLACES: isize = 324;

mod diyfp;

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

use diyfp::DiyFp;

#[inline]
pub fn write<W: io::Write, V: Floating>(wr: &mut W, value: V) -> io::Result<()> {
    value.write(wr)
}

pub trait Floating {
    fn write<W: io::Write>(self, &mut W) -> io::Result<()>;
}

impl Floating for f64 {
    fn write<W: io::Write>(self, wr: &mut W) -> io::Result<()> {
        unsafe { dtoa(wr, self) }
    }
}

impl Floating for f32 {
    fn write<W: io::Write>(self, wr: &mut W) -> io::Result<()> {
        unsafe { dtoa(wr, self as f64) }
    }
}

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

/*
inline void GrisuRound(char* buffer, int len, uint64_t delta, uint64_t rest, uint64_t ten_kappa, uint64_t wp_w) {
    while (rest < wp_w && delta - rest >= ten_kappa &&
           (rest + ten_kappa < wp_w ||  /// closer
            wp_w - rest > rest + ten_kappa - wp_w)) {
        buffer[len - 1]--;
        rest += ten_kappa;
    }
}
*/

#[inline]
unsafe fn grisu_round(buffer: *mut u8, len: isize, delta: u64, mut rest: u64, ten_kappa: u64, wp_w: u64) {
    while rest < wp_w && delta - rest >= ten_kappa &&
           (rest + ten_kappa < wp_w || // closer
            wp_w - rest > rest + ten_kappa - wp_w) {
        *buffer.offset(len - 1) -= 1;
        rest += ten_kappa;
    }
}

/*
inline unsigned CountDecimalDigit32(uint32_t n) {
    // Simple pure C++ implementation was faster than __builtin_clz version in this situation.
    if (n < 10) return 1;
    if (n < 100) return 2;
    if (n < 1000) return 3;
    if (n < 10000) return 4;
    if (n < 100000) return 5;
    if (n < 1000000) return 6;
    if (n < 10000000) return 7;
    if (n < 100000000) return 8;
    // Will not reach 10 digits in DigitGen()
    //if (n < 1000000000) return 9;
    //return 10;
    return 9;
}
*/

#[inline]
fn count_decimal_digit32(n: u32) -> usize {
    if n < 10 { 1 }
    else if n < 100 { 2 }
    else if n < 1000 { 3 }
    else if n < 10000 { 4 }
    else if n < 100000 { 5 }
    else if n < 1000000 { 6 }
    else if n < 10000000 { 7 }
    else if n < 100000000 { 8 }
    // Will not reach 10 digits in digit_gen()
    else { 9 }
}

/*
inline void DigitGen(const DiyFp& W, const DiyFp& Mp, uint64_t delta, char* buffer, int* len, int* K) {
    static const uint32_t kPow10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 };
    const DiyFp one(uint64_t(1) << -Mp.e, Mp.e);
    const DiyFp wp_w = Mp - W;
    uint32_t p1 = static_cast<uint32_t>(Mp.f >> -one.e);
    uint64_t p2 = Mp.f & (one.f - 1);
    unsigned kappa = CountDecimalDigit32(p1); // kappa in [0, 9]
    *len = 0;
*/

// Returns length and k.
#[inline]
unsafe fn digit_gen(w: DiyFp, mp: DiyFp, mut delta: u64, buffer: *mut u8, mut k: isize) -> (isize, isize) {
    static POW10: [u32; 10] = [ 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 ];
    let one = DiyFp::new(1u64 << -mp.e, mp.e);
    let wp_w = mp - w;
    let mut p1 = (mp.f >> -one.e) as u32;
    let mut p2 = mp.f & (one.f - 1);
    let mut kappa = count_decimal_digit32(p1); // kappa in [0, 9]
    let mut len = 0;

    /*
    while (kappa > 0) {
        uint32_t d = 0;
        switch (kappa) {
            case  9: d = p1 /  100000000; p1 %=  100000000; break;
            case  8: d = p1 /   10000000; p1 %=   10000000; break;
            case  7: d = p1 /    1000000; p1 %=    1000000; break;
            case  6: d = p1 /     100000; p1 %=     100000; break;
            case  5: d = p1 /      10000; p1 %=      10000; break;
            case  4: d = p1 /       1000; p1 %=       1000; break;
            case  3: d = p1 /        100; p1 %=        100; break;
            case  2: d = p1 /         10; p1 %=         10; break;
            case  1: d = p1;              p1 =           0; break;
            default:;
        }
        if (d || *len)
            buffer[(*len)++] = static_cast<char>('0' + static_cast<char>(d));
        kappa--;
        uint64_t tmp = (static_cast<uint64_t>(p1) << -one.e) + p2;
        if (tmp <= delta) {
            *K += kappa;
            GrisuRound(buffer, *len, delta, tmp, static_cast<uint64_t>(kPow10[kappa]) << -one.e, wp_w.f);
            return;
        }
    }
    */
    while kappa > 0 {
        let mut d = 0u32;
        match kappa {
            9 => { d = p1 /  100000000; p1 %=  100000000; }
            8 => { d = p1 /   10000000; p1 %=   10000000; }
            7 => { d = p1 /    1000000; p1 %=    1000000; }
            6 => { d = p1 /     100000; p1 %=     100000; }
            5 => { d = p1 /      10000; p1 %=      10000; }
            4 => { d = p1 /       1000; p1 %=       1000; }
            3 => { d = p1 /        100; p1 %=        100; }
            2 => { d = p1 /         10; p1 %=         10; }
            1 => { d = p1;              p1 =           0; }
            _ => {}
        }
        if d != 0 || len != 0 {
            *buffer.offset(len) = b'0' + d as u8;
            len += 1;
        }
        kappa -= 1;
        let tmp = ((p1 as u64) << -one.e) + p2;
        if tmp <= delta {
            k += kappa as isize;
            grisu_round(buffer, len, delta, tmp, (POW10[kappa] as u64) << -one.e, wp_w.f);
            return (len, k);
        }
    }

    // kappa = 0
    /*
    for (;;) {
        p2 *= 10;
        delta *= 10;
        char d = static_cast<char>(p2 >> -one.e);
        if (d || *len)
            buffer[(*len)++] = static_cast<char>('0' + d);
        p2 &= one.f - 1;
        kappa--;
        if (p2 < delta) {
            *K += kappa;
            int index = -static_cast<int>(kappa);
            GrisuRound(buffer, *len, delta, p2, one.f, wp_w.f * (index < 9 ? kPow10[-static_cast<int>(kappa)] : 0));
            return;
        }
    }
    */
    loop {
        p2 *= 10;
        delta *= 10;
        let d = (p2 >> -one.e) as u8;
        if d != 0 || len != 0 {
            *buffer.offset(len) = b'0' + d;
            len += 1;
        }
        p2 &= one.f - 1;
        kappa = kappa.wrapping_sub(1);
        if p2 < delta {
            k += kappa as isize;
            let index = -(kappa as isize);
            grisu_round(buffer, len, delta, p2, one.f, wp_w.f * if index < 9 { POW10[-(kappa as isize) as usize] as u64 } else { 0 });
            return (len, k);
        }
    }
}

/*
inline void Grisu2(double value, char* buffer, int* length, int* K) {
    const DiyFp v(value);
    DiyFp w_m, w_p;
    v.NormalizedBoundaries(&w_m, &w_p);

    const DiyFp c_mk = GetCachedPower(w_p.e, K);
    const DiyFp W = v.Normalize() * c_mk;
    DiyFp Wp = w_p * c_mk;
    DiyFp Wm = w_m * c_mk;
    Wm.f++;
    Wp.f--;
    DigitGen(W, Wp, Wp.f - Wm.f, buffer, length, K);
}
*/

// Returns length and k.
#[inline]
unsafe fn grisu2(value: f64, buffer: *mut u8) -> (isize, isize) {
    let v = DiyFp::from_f64(value);
    let (w_m, w_p) = v.normalized_boundaries();

    let (c_mk, k) = diyfp::get_cached_power(w_p.e);
    let w = v.normalize() * c_mk;
    let mut wp = w_p * c_mk;
    let mut wm = w_m * c_mk;
    wm.f += 1;
    wp.f -= 1;
    digit_gen(w, wp, wp.f - wm.f, buffer, k)
}

/*
inline char* WriteExponent(int K, char* buffer) {
    if (K < 0) {
        *buffer++ = '-';
        K = -K;
    }

    if (K >= 100) {
        *buffer++ = static_cast<char>('0' + static_cast<char>(K / 100));
        K %= 100;
        const char* d = GetDigitsLut() + K * 2;
        *buffer++ = d[0];
        *buffer++ = d[1];
    }
    else if (K >= 10) {
        const char* d = GetDigitsLut() + K * 2;
        *buffer++ = d[0];
        *buffer++ = d[1];
    }
    else
        *buffer++ = static_cast<char>('0' + static_cast<char>(K));

    return buffer;
}
*/

#[inline]
unsafe fn write_exponent(mut k: isize, mut buffer: *mut u8) -> *mut u8 {
    if k < 0 {
        *buffer = b'-';
        buffer = buffer.offset(1);
        k = -k;
    }

    if k >= 100 {
        *buffer = b'0' + (k / 100) as u8;
        k %= 100;
        let d = DEC_DIGITS_LUT.as_ptr().offset(k * 2);
        ptr::copy_nonoverlapping(d, buffer.offset(1), 2);
        buffer.offset(3)
    } else if k >= 10 {
        let d = DEC_DIGITS_LUT.as_ptr().offset(k * 2);
        ptr::copy_nonoverlapping(d, buffer, 2);
        buffer.offset(2)
    } else {
        *buffer = b'0' + k as u8;
        buffer.offset(1)
    }
}

/*
inline char* Prettify(char* buffer, int length, int k, int maxDecimalPlaces) {
    const int kk = length + k;  // 10^(kk-1) <= v < 10^kk
*/

#[inline]
unsafe fn prettify(buffer: *mut u8, length: isize, k: isize) -> *mut u8 {
    let kk = length + k; // 10^(kk-1) <= v < 10^kk

    /*
    if (0 <= k && kk <= 21) {
        // 1234e7 -> 12340000000
        for (int i = length; i < kk; i++)
            buffer[i] = '0';
        buffer[kk] = '.';
        buffer[kk + 1] = '0';
        return &buffer[kk + 2];
    }
    */
    if 0 <= k && kk <= 21 {
        // 1234e7 -> 12340000000
        for i in length..kk {
            *buffer.offset(i) = b'0';
        }
        buffer.offset(kk)
    }

    /*
    else if (0 < kk && kk <= 21) {
        // 1234e-2 -> 12.34
        std::memmove(&buffer[kk + 1], &buffer[kk], static_cast<size_t>(length - kk));
        buffer[kk] = '.';
        if (0 > k + maxDecimalPlaces) {
            // When maxDecimalPlaces = 2, 1.2345 -> 1.23, 1.102 -> 1.1
            // Remove extra trailing zeros (at least one) after truncation.
            for (int i = kk + maxDecimalPlaces; i > kk + 1; i--)
                if (buffer[i] != '0')
                    return &buffer[i + 1];
            return &buffer[kk + 2]; // Reserve one zero
        }
        else
            return &buffer[length + 1];
    }
    */
    else if 0 < kk && kk <= 21 {
        // 1234e-2 -> 12.34
        ptr::copy(buffer.offset(kk), buffer.offset(kk + 1), (length - kk) as usize);
        *buffer.offset(kk) = b'.';
        if 0 > k + MAX_DECIMAL_PLACES {
            // When MAX_DECIMAL_PLACES = 2, 1.2345 -> 1.23, 1.102 -> 1.1
            // Remove extra trailing zeros (at least one) after truncation.
            for i in (kk + 2 .. kk + MAX_DECIMAL_PLACES + 1).rev() {
                if *buffer.offset(i) != b'0' {
                    return buffer.offset(i + 1);
                }
            }
            buffer.offset(kk + 2) // Reserve one zero
        } else {
            buffer.offset(length + 1)
        }
    }

    /*
    else if (-6 < kk && kk <= 0) {
        // 1234e-6 -> 0.001234
        const int offset = 2 - kk;
        std::memmove(&buffer[offset], &buffer[0], static_cast<size_t>(length));
        buffer[0] = '0';
        buffer[1] = '.';
        for (int i = 2; i < offset; i++)
            buffer[i] = '0';
        if (length - kk > maxDecimalPlaces) {
            // When maxDecimalPlaces = 2, 0.123 -> 0.12, 0.102 -> 0.1
            // Remove extra trailing zeros (at least one) after truncation.
            for (int i = maxDecimalPlaces + 1; i > 2; i--)
                if (buffer[i] != '0')
                    return &buffer[i + 1];
            return &buffer[3]; // Reserve one zero
        }
        else
            return &buffer[length + offset];
    }
    */
    else if -6 < kk && kk <= 0 {
        // 1234e-6 -> 0.001234
        let offset = 2 - kk;
        ptr::copy(buffer, buffer.offset(offset), length as usize);
        *buffer = b'0';
        *buffer.offset(1) = b'.';
        for i in 2..offset {
            *buffer.offset(i) = b'0';
        }
        if length - kk > MAX_DECIMAL_PLACES {
            // When MAX_DECIMAL_PLACES = 2, 0.123 -> 0.12, 0.102 -> 0.1
            // Remove extra trailing zeros (at least one) after truncation.
            for i in (3 .. MAX_DECIMAL_PLACES + 2).rev() {
                if *buffer.offset(i) != b'0' {
                    return buffer.offset(i + 1);
                }
            }
            buffer.offset(3) // Reserve one zero
        } else {
            buffer.offset(length + offset)
        }
    }

    /*
    else if (kk < -maxDecimalPlaces) {
        // Truncate to zero
        buffer[0] = '0';
        buffer[1] = '.';
        buffer[2] = '0';
        return &buffer[3];
    }
    */
    else if kk < -MAX_DECIMAL_PLACES {
        *buffer = b'0';
        buffer.offset(1)
    }

    /*
    else if (length == 1) {
        // 1e30
        buffer[1] = 'e';
        return WriteExponent(kk - 1, &buffer[2]);
    }
    */
    else if length == 1 {
        // 1e30
        *buffer.offset(1) = b'e';
        write_exponent(kk - 1, buffer.offset(2))
    }

    /*
    else {
        // 1234e30 -> 1.234e33
        std::memmove(&buffer[2], &buffer[1], static_cast<size_t>(length - 1));
        buffer[1] = '.';
        buffer[length + 1] = 'e';
        return WriteExponent(kk - 1, &buffer[0 + length + 2]);
    }
    */
    else {
        // 1234e30 -> 1.234e33
        ptr::copy(buffer.offset(1), buffer.offset(2), (length - 1) as usize);
        *buffer.offset(1) = b'.';
        *buffer.offset(length + 1) = b'e';
        write_exponent(kk - 1, buffer.offset(length + 2))
    }
}

/*
inline char* dtoa(double value, char* buffer, int maxDecimalPlaces = 324) {
    RAPIDJSON_ASSERT(maxDecimalPlaces >= 1);
    Double d(value);
    if (d.IsZero()) {
        if (d.Sign())
            *buffer++ = '-';     // -0.0, Issue #289
        buffer[0] = '0';
        buffer[1] = '.';
        buffer[2] = '0';
        return &buffer[3];
    }
    else {
        if (value < 0) {
            *buffer++ = '-';
            value = -value;
        }
        int length, K;
        Grisu2(value, buffer, &length, &K);
        return Prettify(buffer, length, K, maxDecimalPlaces);
    }
}
*/

#[inline]
unsafe fn dtoa<W: io::Write>(wr: &mut W, mut value: f64) -> io::Result<()> {
    if value == 0.0 {
        if value.is_sign_negative() {
            wr.write_all(b"-0")
        } else {
            wr.write_all(b"0")
        }
    } else {
        if value < 0.0 {
            try!(wr.write_all(b"-"));
            value = -value;
        }
        let mut buffer: [u8; 24] = mem::uninitialized();
        let buf_ptr = buffer.as_mut_ptr();
        let (length, k) = grisu2(value, buf_ptr);
        let end = prettify(buf_ptr, length, k);
        wr.write_all(slice::from_raw_parts(
            buf_ptr, end as usize - buf_ptr as usize
        ))
    }
}