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    // This file comes from the `dtoa` port by David Tolnay:
    // https://github.com/dtolnay/dtoa
    //
    // 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.

    use std::{mem, ops};

    const DIY_SIGNIFICAND_SIZE: isize = 64;
    const DP_SIGNIFICAND_SIZE: isize = 52;
    const DP_EXPONENT_BIAS: isize = 0x3FF + DP_SIGNIFICAND_SIZE;
    const DP_MIN_EXPONENT: isize = -DP_EXPONENT_BIAS;
    const DP_EXPONENT_MASK: u64 = 0x7FF0000000000000;
    const DP_SIGNIFICAND_MASK: u64 = 0x000FFFFFFFFFFFFF;
    const DP_HIDDEN_BIT: u64 = 0x0010000000000000;

    #[derive(Copy, Clone, Debug)]
    pub struct DiyFp {
        pub f: u64,
        pub e: isize,
    }

    impl DiyFp {
        pub fn new(f: u64, e: isize) -> Self {
            DiyFp { f: f, e: e }
        }

        /*
        explicit DiyFp(double d) {
            union {
                double d;
                uint64_t u64;
            } u = { d };

            int biased_e = static_cast<int>((u.u64 & kDpExponentMask) >> kDpSignificandSize);
            uint64_t significand = (u.u64 & kDpSignificandMask);
            if (biased_e != 0) {
                f = significand + kDpHiddenBit;
                e = biased_e - kDpExponentBias;
            }
            else {
                f = significand;
                e = kDpMinExponent + 1;
            }
        }
        */
        pub unsafe fn from_f64(d: f64) -> Self {
            let u: u64 = mem::transmute(d);

            let biased_e = ((u & DP_EXPONENT_MASK) >> DP_SIGNIFICAND_SIZE) as isize;
            let significand = u & DP_SIGNIFICAND_MASK;
            if biased_e != 0 {
                DiyFp {
                    f: significand + DP_HIDDEN_BIT,
                    e: biased_e - DP_EXPONENT_BIAS,
                }
            } else {
                DiyFp {
                    f: significand,
                    e: DP_MIN_EXPONENT + 1,
                }
            }
        }

        /*
        DiyFp Normalize() const {
            DiyFp res = *this;
            while (!(res.f & (static_cast<uint64_t>(1) << 63))) {
                res.f <<= 1;
                res.e--;
            }
            return res;
        }
        */
        pub fn normalize(self) -> DiyFp {
            let mut res = self;
            while (res.f & (1u64 << 63)) == 0 {
                res.f <<= 1;
                res.e -= 1;
            }
            res
        }

        /*
        DiyFp NormalizeBoundary() const {
            DiyFp res = *this;
            while (!(res.f & (kDpHiddenBit << 1))) {
                res.f <<= 1;
                res.e--;
            }
            res.f <<= (kDiySignificandSize - kDpSignificandSize - 2);
            res.e = res.e - (kDiySignificandSize - kDpSignificandSize - 2);
            return res;
        }
        */
        pub fn normalize_boundary(self) -> DiyFp {
            let mut res = self;
            while (res.f & DP_HIDDEN_BIT << 1) == 0 {
                res.f <<= 1;
                res.e -= 1;
            }
            res.f <<= DIY_SIGNIFICAND_SIZE - DP_SIGNIFICAND_SIZE - 2;
            res.e -= DIY_SIGNIFICAND_SIZE - DP_SIGNIFICAND_SIZE - 2;
            res
        }

        /*
        void NormalizedBoundaries(DiyFp* minus, DiyFp* plus) const {
            DiyFp pl = DiyFp((f << 1) + 1, e - 1).NormalizeBoundary();
            DiyFp mi = (f == kDpHiddenBit) ? DiyFp((f << 2) - 1, e - 2) : DiyFp((f << 1) - 1, e - 1);
            mi.f <<= mi.e - pl.e;
            mi.e = pl.e;
            *plus = pl;
            *minus = mi;
        }
        */
        pub fn normalized_boundaries(self) -> (DiyFp, DiyFp) {
            let pl = DiyFp::new((self.f << 1) + 1, self.e - 1).normalize_boundary();
            let mut mi = if self.f == DP_HIDDEN_BIT {
                DiyFp::new((self.f << 2) - 1, self.e - 2)
            } else {
                DiyFp::new((self.f << 1) - 1, self.e - 1)
            };
            mi.f <<= mi.e - pl.e;
            mi.e = pl.e;
            (mi, pl)
        }
    }

    impl ops::Sub for DiyFp {
        type Output = DiyFp;
        fn sub(self, rhs: DiyFp) -> DiyFp {
            DiyFp {
                f: self.f - rhs.f,
                e: self.e,
            }
        }
    }

    impl ops::Mul for DiyFp {
        type Output = DiyFp;
        fn mul(self, rhs: DiyFp) -> DiyFp {
            let m32 = 0xFFFFFFFFu64;
            let a = self.f >> 32;
            let b = self.f & m32;
            let c = rhs.f >> 32;
            let d = rhs.f & m32;
            let ac = a * c;
            let bc = b * c;
            let ad = a * d;
            let bd = b * d;
            let mut tmp = (bd >> 32) + (ad & m32) + (bc & m32);
            tmp += 1u64 << 31; // mult_round
            DiyFp {
                f: ac + (ad >> 32) + (bc >> 32) + (tmp >> 32),
                e: self.e + rhs.e + 64,
            }
        }
    }

    fn get_cached_power_by_index(index: usize) -> DiyFp {
        // 10^-348, 10^-340, ..., 10^340
        static CACHED_POWERS_F: [u64; 87] = [
            0xfa8fd5a0081c0288, 0xbaaee17fa23ebf76,
            0x8b16fb203055ac76, 0xcf42894a5dce35ea,
            0x9a6bb0aa55653b2d, 0xe61acf033d1a45df,
            0xab70fe17c79ac6ca, 0xff77b1fcbebcdc4f,
            0xbe5691ef416bd60c, 0x8dd01fad907ffc3c,
            0xd3515c2831559a83, 0x9d71ac8fada6c9b5,
            0xea9c227723ee8bcb, 0xaecc49914078536d,
            0x823c12795db6ce57, 0xc21094364dfb5637,
            0x9096ea6f3848984f, 0xd77485cb25823ac7,
            0xa086cfcd97bf97f4, 0xef340a98172aace5,
            0xb23867fb2a35b28e, 0x84c8d4dfd2c63f3b,
            0xc5dd44271ad3cdba, 0x936b9fcebb25c996,
            0xdbac6c247d62a584, 0xa3ab66580d5fdaf6,
            0xf3e2f893dec3f126, 0xb5b5ada8aaff80b8,
            0x87625f056c7c4a8b, 0xc9bcff6034c13053,
            0x964e858c91ba2655, 0xdff9772470297ebd,
            0xa6dfbd9fb8e5b88f, 0xf8a95fcf88747d94,
            0xb94470938fa89bcf, 0x8a08f0f8bf0f156b,
            0xcdb02555653131b6, 0x993fe2c6d07b7fac,
            0xe45c10c42a2b3b06, 0xaa242499697392d3,
            0xfd87b5f28300ca0e, 0xbce5086492111aeb,
            0x8cbccc096f5088cc, 0xd1b71758e219652c,
            0x9c40000000000000, 0xe8d4a51000000000,
            0xad78ebc5ac620000, 0x813f3978f8940984,
            0xc097ce7bc90715b3, 0x8f7e32ce7bea5c70,
            0xd5d238a4abe98068, 0x9f4f2726179a2245,
            0xed63a231d4c4fb27, 0xb0de65388cc8ada8,
            0x83c7088e1aab65db, 0xc45d1df942711d9a,
            0x924d692ca61be758, 0xda01ee641a708dea,
            0xa26da3999aef774a, 0xf209787bb47d6b85,
            0xb454e4a179dd1877, 0x865b86925b9bc5c2,
            0xc83553c5c8965d3d, 0x952ab45cfa97a0b3,
            0xde469fbd99a05fe3, 0xa59bc234db398c25,
            0xf6c69a72a3989f5c, 0xb7dcbf5354e9bece,
            0x88fcf317f22241e2, 0xcc20ce9bd35c78a5,
            0x98165af37b2153df, 0xe2a0b5dc971f303a,
            0xa8d9d1535ce3b396, 0xfb9b7cd9a4a7443c,
            0xbb764c4ca7a44410, 0x8bab8eefb6409c1a,
            0xd01fef10a657842c, 0x9b10a4e5e9913129,
            0xe7109bfba19c0c9d, 0xac2820d9623bf429,
            0x80444b5e7aa7cf85, 0xbf21e44003acdd2d,
            0x8e679c2f5e44ff8f, 0xd433179d9c8cb841,
            0x9e19db92b4e31ba9, 0xeb96bf6ebadf77d9,
            0xaf87023b9bf0ee6b,
        ];
        static CACHED_POWERS_E: [i16; 87] = [
            -1220, -1193, -1166, -1140, -1113, -1087, -1060, -1034, -1007,  -980,
            -954,  -927,  -901,  -874,  -847,  -821,  -794,  -768,  -741,  -715,
            -688,  -661,  -635,  -608,  -582,  -555,  -529,  -502,  -475,  -449,
            -422,  -396,  -369,  -343,  -316,  -289,  -263,  -236,  -210,  -183,
            -157,  -130,  -103,   -77,   -50,   -24,     3,    30,    56,    83,
            109,   136,   162,   189,   216,   242,   269,   295,   322,   348,
            375,   402,   428,   455,   481,   508,   534,   561,   588,   614,
            641,   667,   694,   720,   747,   774,   800,   827,   853,   880,
            907,   933,   960,   986,  1013,  1039,  1066,
        ];
        DiyFp::new(CACHED_POWERS_F[index], CACHED_POWERS_E[index] as isize)
    }

    /*
    inline DiyFp GetCachedPower(int e, int* K) {
        //int k = static_cast<int>(ceil((-61 - e) * 0.30102999566398114)) + 374;
        double dk = (-61 - e) * 0.30102999566398114 + 347;  // dk must be positive, so can do ceiling in positive
        int k = static_cast<int>(dk);
        if (dk - k > 0.0)
            k++;

        unsigned index = static_cast<unsigned>((k >> 3) + 1);
        *K = -(-348 + static_cast<int>(index << 3));    // decimal exponent no need lookup table

        return GetCachedPowerByIndex(index);
    }
    */
    #[inline]
    pub fn get_cached_power(e: isize) -> (DiyFp, isize) {
        let dk = (-61 - e) as f64 * 0.30102999566398114f64 + 347f64; // dk must be positive, so can do ceiling in positive
        let mut k = dk as isize;
        if dk - k as f64 > 0.0 {
            k += 1;
        }

        let index = ((k >> 3) + 1) as usize;
        let k = -(-348 + (index << 3) as isize); // decimal exponent no need lookup table

        (get_cached_power_by_index(index), k)
    }