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 // Copyright 2018 Ulf Adams
 //
 // The contents of this file may be used under the terms of the Apache License,
 // Version 2.0.
 //
 //    (See accompanying file LICENSE-Apache or copy at
 //     http://www.apache.org/licenses/LICENSE-2.0)
 //
 // Alternatively, the contents of this file may be used under the terms of
 // the Boost Software License, Version 1.0.
 //    (See accompanying file LICENSE-Boost or copy at
 //     https://www.boost.org/LICENSE_1_0.txt)
 //
 // Unless required by applicable law or agreed to in writing, this software
 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 // KIND, either express or implied.
 
 // Runtime compiler options:
 // -DRYU_DEBUG Generate verbose debugging output to stdout.
 //
 // -DRYU_ONLY_64_BIT_OPS Avoid using uint128_t or 64-bit intrinsics. Slower,
 //     depending on your compiler.
 //
 // -DRYU_OPTIMIZE_SIZE Use smaller lookup tables. Instead of storing every
 //     required power of 5, only store every 26th entry, and compute
 //     intermediate values with a multiplication. This reduces the lookup table
 //     size by about 10x (only one case, and only double) at the cost of some
 //     performance. Currently requires MSVC intrinsics.
 
 /*
     This is a derivative work
 */
 
 #ifndef BOOST_JSON_DETAIL_RYU_IMPL_D2S_IPP
 #define BOOST_JSON_DETAIL_RYU_IMPL_D2S_IPP
 
 #include <boost/json/detail/ryu/ryu.hpp>
 #include <cstdlib>
 #include <cstring>
 
 #ifdef RYU_DEBUG
 #include <stdio.h>
 #endif
 
 // ABSL avoids uint128_t on Win32 even if __SIZEOF_INT128__ is defined.
 // Let's do the same for now.
 #if defined(__SIZEOF_INT128__) && !defined(_MSC_VER) && !defined(RYU_ONLY_64_BIT_OPS)
 #define BOOST_JSON_RYU_HAS_UINT128
 #elif defined(_MSC_VER) && !defined(RYU_ONLY_64_BIT_OPS) && defined(_M_X64)
 #define BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS
 #endif
 
 #include <boost/json/detail/ryu/detail/common.hpp>
 #include <boost/json/detail/ryu/detail/digit_table.hpp>
 #include <boost/json/detail/ryu/detail/d2s.hpp>
 #include <boost/json/detail/ryu/detail/d2s_intrinsics.hpp>
 
 namespace boost {
 namespace json {
 namespace detail {
 
 namespace ryu {
 namespace detail {
 
 // We need a 64x128-bit multiplication and a subsequent 128-bit shift.
 // Multiplication:
 //   The 64-bit factor is variable and passed in, the 128-bit factor comes
 //   from a lookup table. We know that the 64-bit factor only has 55
 //   significant bits (i.e., the 9 topmost bits are zeros). The 128-bit
 //   factor only has 124 significant bits (i.e., the 4 topmost bits are
 //   zeros).
 // Shift:
 //   In principle, the multiplication result requires 55 + 124 = 179 bits to
 //   represent. However, we then shift this value to the right by j, which is
 //   at least j >= 115, so the result is guaranteed to fit into 179 - 115 = 64
 //   bits. This means that we only need the topmost 64 significant bits of
 //   the 64x128-bit multiplication.
 //
 // There are several ways to do this:
 // 1. Best case: the compiler exposes a 128-bit type.
 //    We perform two 64x64-bit multiplications, add the higher 64 bits of the
 //    lower result to the higher result, and shift by j - 64 bits.
 //
 //    We explicitly cast from 64-bit to 128-bit, so the compiler can tell
 //    that these are only 64-bit inputs, and can map these to the best
 //    possible sequence of assembly instructions.
 //    x64 machines happen to have matching assembly instructions for
 //    64x64-bit multiplications and 128-bit shifts.
 //
 // 2. Second best case: the compiler exposes intrinsics for the x64 assembly
 //    instructions mentioned in 1.
 //
 // 3. We only have 64x64 bit instructions that return the lower 64 bits of
 //    the result, i.e., we have to use plain C.
 //    Our inputs are less than the full width, so we have three options:
 //    a. Ignore this fact and just implement the intrinsics manually.
 //    b. Split both into 31-bit pieces, which guarantees no internal overflow,
 //       but requires extra work upfront (unless we change the lookup table).
 //    c. Split only the first factor into 31-bit pieces, which also guarantees
 //       no internal overflow, but requires extra work since the intermediate
 //       results are not perfectly aligned.
 #if defined(BOOST_JSON_RYU_HAS_UINT128)
 
 // Best case: use 128-bit type.
 inline
 std::uint64_t
     mulShift(
     const std::uint64_t m,
     const std::uint64_t* const mul,
     const std::int32_t j) noexcept
 {
     const uint128_t b0 = ((uint128_t) m) * mul[0];
     const uint128_t b2 = ((uint128_t) m) * mul[1];
     return (std::uint64_t) (((b0 >> 64) + b2) >> (j - 64));
 }
 
 inline
 uint64_t
 mulShiftAll(
     const std::uint64_t m,
     const std::uint64_t* const mul,
     std::int32_t const j,
     std::uint64_t* const vp,
     std::uint64_t* const vm,
     const std::uint32_t mmShift) noexcept
 {
 //  m <<= 2;
 //  uint128_t b0 = ((uint128_t) m) * mul[0]; // 0
 //  uint128_t b2 = ((uint128_t) m) * mul[1]; // 64
 //
 //  uint128_t hi = (b0 >> 64) + b2;
 //  uint128_t lo = b0 & 0xffffffffffffffffull;
 //  uint128_t factor = (((uint128_t) mul[1]) << 64) + mul[0];
 //  uint128_t vpLo = lo + (factor << 1);
 //  *vp = (std::uint64_t) ((hi + (vpLo >> 64)) >> (j - 64));
 //  uint128_t vmLo = lo - (factor << mmShift);
 //  *vm = (std::uint64_t) ((hi + (vmLo >> 64) - (((uint128_t) 1ull) << 64)) >> (j - 64));
 //  return (std::uint64_t) (hi >> (j - 64));
     *vp = mulShift(4 * m + 2, mul, j);
     *vm = mulShift(4 * m - 1 - mmShift, mul, j);
     return mulShift(4 * m, mul, j);
 }
 
 #elif defined(BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS)
 
 inline
 std::uint64_t
 mulShift(
     const std::uint64_t m,
     const std::uint64_t* const mul,
     const std::int32_t j) noexcept
 {
     // m is maximum 55 bits
     std::uint64_t high1;                                   // 128
     std::uint64_t const low1 = umul128(m, mul[1], &high1); // 64
     std::uint64_t high0;                                   // 64
     umul128(m, mul[0], &high0);                            // 0
     std::uint64_t const sum = high0 + low1;
     if (sum < high0)
         ++high1; // overflow into high1
     return shiftright128(sum, high1, j - 64);
 }
 
 inline
 std::uint64_t
 mulShiftAll(
     const std::uint64_t m,
     const std::uint64_t* const mul,
     const std::int32_t j,
     std::uint64_t* const vp,
     std::uint64_t* const vm,
     const std::uint32_t mmShift) noexcept
 {
     *vp = mulShift(4 * m + 2, mul, j);
     *vm = mulShift(4 * m - 1 - mmShift, mul, j);
     return mulShift(4 * m, mul, j);
 }
 
 #else // !defined(BOOST_JSON_RYU_HAS_UINT128) && !defined(BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS)
 
 inline
 std::uint64_t
 mulShiftAll(
     std::uint64_t m,
     const std::uint64_t* const mul,
     const std::int32_t j,
     std::uint64_t* const vp,
     std::uint64_t* const vm,
     const std::uint32_t mmShift)
 {
     m <<= 1;
     // m is maximum 55 bits
     std::uint64_t tmp;
     std::uint64_t const lo = umul128(m, mul[0], &tmp);
     std::uint64_t hi;
     std::uint64_t const mid = tmp + umul128(m, mul[1], &hi);
     hi += mid < tmp; // overflow into hi
 
     const std::uint64_t lo2 = lo + mul[0];
     const std::uint64_t mid2 = mid + mul[1] + (lo2 < lo);
     const std::uint64_t hi2 = hi + (mid2 < mid);
     *vp = shiftright128(mid2, hi2, (std::uint32_t)(j - 64 - 1));
 
     if (mmShift == 1)
     {
         const std::uint64_t lo3 = lo - mul[0];
         const std::uint64_t mid3 = mid - mul[1] - (lo3 > lo);
         const std::uint64_t hi3 = hi - (mid3 > mid);
         *vm = shiftright128(mid3, hi3, (std::uint32_t)(j - 64 - 1));
     }
     else
     {
         const std::uint64_t lo3 = lo + lo;
         const std::uint64_t mid3 = mid + mid + (lo3 < lo);
         const std::uint64_t hi3 = hi + hi + (mid3 < mid);
         const std::uint64_t lo4 = lo3 - mul[0];
         const std::uint64_t mid4 = mid3 - mul[1] - (lo4 > lo3);
         const std::uint64_t hi4 = hi3 - (mid4 > mid3);
         *vm = shiftright128(mid4, hi4, (std::uint32_t)(j - 64));
     }
 
     return shiftright128(mid, hi, (std::uint32_t)(j - 64 - 1));
 }
 
 #endif // BOOST_JSON_RYU_HAS_64_BIT_INTRINSICS
 
 inline
 std::uint32_t
 decimalLength17(
     const std::uint64_t v)
 {
     // This is slightly faster than a loop.
     // The average output length is 16.38 digits, so we check high-to-low.
     // Function precondition: v is not an 18, 19, or 20-digit number.
     // (17 digits are sufficient for round-tripping.)
     BOOST_ASSERT(v < 100000000000000000L);
     if (v >= 10000000000000000L) { return 17; }
     if (v >= 1000000000000000L) { return 16; }
     if (v >= 100000000000000L) { return 15; }
     if (v >= 10000000000000L) { return 14; }
     if (v >= 1000000000000L) { return 13; }
     if (v >= 100000000000L) { return 12; }
     if (v >= 10000000000L) { return 11; }
     if (v >= 1000000000L) { return 10; }
     if (v >= 100000000L) { return 9; }
     if (v >= 10000000L) { return 8; }
     if (v >= 1000000L) { return 7; }
     if (v >= 100000L) { return 6; }
     if (v >= 10000L) { return 5; }
     if (v >= 1000L) { return 4; }
     if (v >= 100L) { return 3; }
     if (v >= 10L) { return 2; }
     return 1;
 }
 
 // A floating decimal representing m * 10^e.
 struct floating_decimal_64
 {
     std::uint64_t mantissa;
     // Decimal exponent's range is -324 to 308
     // inclusive, and can fit in a short if needed.
     std::int32_t exponent;
 };
 
 inline
 floating_decimal_64
 d2d(
     const std::uint64_t ieeeMantissa,
     const std::uint32_t ieeeExponent)
 {
     std::int32_t e2;
     std::uint64_t m2;
     if (ieeeExponent == 0)
     {
         // We subtract 2 so that the bounds computation has 2 additional bits.
         e2 = 1 - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS - 2;
         m2 = ieeeMantissa;
     }
     else
     {
         e2 = (std::int32_t)ieeeExponent - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS - 2;
         m2 = (1ull << DOUBLE_MANTISSA_BITS) | ieeeMantissa;
     }
     const bool even = (m2 & 1) == 0;
     const bool acceptBounds = even;
 
 #ifdef RYU_DEBUG
     printf("-> %" PRIu64 " * 2^%d\n", m2, e2 + 2);
 #endif
 
     // Step 2: Determine the interval of valid decimal representations.
     const std::uint64_t mv = 4 * m2;
     // Implicit bool -> int conversion. True is 1, false is 0.
     const std::uint32_t mmShift = ieeeMantissa != 0 || ieeeExponent <= 1;
     // We would compute mp and mm like this:
     // uint64_t mp = 4 * m2 + 2;
     // uint64_t mm = mv - 1 - mmShift;
 
     // Step 3: Convert to a decimal power base using 128-bit arithmetic.
     std::uint64_t vr, vp, vm;
     std::int32_t e10;
     bool vmIsTrailingZeros = false;
     bool vrIsTrailingZeros = false;
     if (e2 >= 0) {
         // I tried special-casing q == 0, but there was no effect on performance.
         // This expression is slightly faster than max(0, log10Pow2(e2) - 1).
         const std::uint32_t q = log10Pow2(e2) - (e2 > 3);
         e10 = (std::int32_t)q;
         const std::int32_t k = DOUBLE_POW5_INV_BITCOUNT + pow5bits((int32_t)q) - 1;
         const std::int32_t i = -e2 + (std::int32_t)q + k;
 #if defined(BOOST_JSON_RYU_OPTIMIZE_SIZE)
         uint64_t pow5[2];
         double_computeInvPow5(q, pow5);
         vr = mulShiftAll(m2, pow5, i, &vp, &vm, mmShift);
 #else
         vr = mulShiftAll(m2, DOUBLE_POW5_INV_SPLIT()[q], i, &vp, &vm, mmShift);
 #endif
 #ifdef RYU_DEBUG
         printf("%" PRIu64 " * 2^%d / 10^%u\n", mv, e2, q);
         printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
 #endif
         if (q <= 21)
         {
             // This should use q <= 22, but I think 21 is also safe. Smaller values
             // may still be safe, but it's more difficult to reason about them.
             // Only one of mp, mv, and mm can be a multiple of 5, if any.
             const std::uint32_t mvMod5 = ((std::uint32_t)mv) - 5 * ((std::uint32_t)div5(mv));
             if (mvMod5 == 0)
             {
                 vrIsTrailingZeros = multipleOfPowerOf5(mv, q);
             }
             else if (acceptBounds)
             {
                 // Same as min(e2 + (~mm & 1), pow5Factor(mm)) >= q
                 // <=> e2 + (~mm & 1) >= q && pow5Factor(mm) >= q
                 // <=> true && pow5Factor(mm) >= q, since e2 >= q.
                 vmIsTrailingZeros = multipleOfPowerOf5(mv - 1 - mmShift, q);
             }
             else
             {
                 // Same as min(e2 + 1, pow5Factor(mp)) >= q.
                 vp -= multipleOfPowerOf5(mv + 2, q);
             }
         }
     }
     else
     {
         // This expression is slightly faster than max(0, log10Pow5(-e2) - 1).
         const std::uint32_t q = log10Pow5(-e2) - (-e2 > 1);
         e10 = (std::int32_t)q + e2;
         const std::int32_t i = -e2 - (std::int32_t)q;
         const std::int32_t k = pow5bits(i) - DOUBLE_POW5_BITCOUNT;
         const std::int32_t j = (std::int32_t)q - k;
 #if defined(BOOST_JSON_RYU_OPTIMIZE_SIZE)
         std::uint64_t pow5[2];
         double_computePow5(i, pow5);
         vr = mulShiftAll(m2, pow5, j, &vp, &vm, mmShift);
 #else
         vr = mulShiftAll(m2, DOUBLE_POW5_SPLIT()[i], j, &vp, &vm, mmShift);
 #endif
 #ifdef RYU_DEBUG
         printf("%" PRIu64 " * 5^%d / 10^%u\n", mv, -e2, q);
         printf("%u %d %d %d\n", q, i, k, j);
         printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
 #endif
         if (q <= 1)
         {
             // {vr,vp,vm} is trailing zeros if {mv,mp,mm} has at least q trailing 0 bits.
             // mv = 4 * m2, so it always has at least two trailing 0 bits.
             vrIsTrailingZeros = true;
             if (acceptBounds)
             {
                 // mm = mv - 1 - mmShift, so it has 1 trailing 0 bit iff mmShift == 1.
                 vmIsTrailingZeros = mmShift == 1;
             }
             else
             {
                 // mp = mv + 2, so it always has at least one trailing 0 bit.
                 --vp;
             }
         }
         else if (q < 63)
         {
             // TODO(ulfjack): Use a tighter bound here.
             // We want to know if the full product has at least q trailing zeros.
             // We need to compute min(p2(mv), p5(mv) - e2) >= q
             // <=> p2(mv) >= q && p5(mv) - e2 >= q
             // <=> p2(mv) >= q (because -e2 >= q)
             vrIsTrailingZeros = multipleOfPowerOf2(mv, q);
 #ifdef RYU_DEBUG
             printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
 #endif
         }
     }
 #ifdef RYU_DEBUG
     printf("e10=%d\n", e10);
     printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
     printf("vm is trailing zeros=%s\n", vmIsTrailingZeros ? "true" : "false");
     printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
 #endif
 
     // Step 4: Find the shortest decimal representation in the interval of valid representations.
     std::int32_t removed = 0;
     std::uint8_t lastRemovedDigit = 0;
     std::uint64_t output;
     // On average, we remove ~2 digits.
     if (vmIsTrailingZeros || vrIsTrailingZeros)
     {
         // General case, which happens rarely (~0.7%).
         for (;;)
         {
             const std::uint64_t vpDiv10 = div10(vp);
             const std::uint64_t vmDiv10 = div10(vm);
             if (vpDiv10 <= vmDiv10)
                 break;
             const std::uint32_t vmMod10 = ((std::uint32_t)vm) - 10 * ((std::uint32_t)vmDiv10);
             const std::uint64_t vrDiv10 = div10(vr);
             const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
             vmIsTrailingZeros &= vmMod10 == 0;
             vrIsTrailingZeros &= lastRemovedDigit == 0;
             lastRemovedDigit = (uint8_t)vrMod10;
             vr = vrDiv10;
             vp = vpDiv10;
             vm = vmDiv10;
             ++removed;
         }
 #ifdef RYU_DEBUG
         printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
         printf("d-10=%s\n", vmIsTrailingZeros ? "true" : "false");
 #endif
         if (vmIsTrailingZeros)
         {
             for (;;)
             {
                 const std::uint64_t vmDiv10 = div10(vm);
                 const std::uint32_t vmMod10 = ((std::uint32_t)vm) - 10 * ((std::uint32_t)vmDiv10);
                 if (vmMod10 != 0)
                     break;
                 const std::uint64_t vpDiv10 = div10(vp);
                 const std::uint64_t vrDiv10 = div10(vr);
                 const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
                 vrIsTrailingZeros &= lastRemovedDigit == 0;
                 lastRemovedDigit = (uint8_t)vrMod10;
                 vr = vrDiv10;
                 vp = vpDiv10;
                 vm = vmDiv10;
                 ++removed;
             }
         }
 #ifdef RYU_DEBUG
         printf("%" PRIu64 " %d\n", vr, lastRemovedDigit);
         printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
 #endif
         if (vrIsTrailingZeros && lastRemovedDigit == 5 && vr % 2 == 0)
         {
             // Round even if the exact number is .....50..0.
             lastRemovedDigit = 4;
         }
         // We need to take vr + 1 if vr is outside bounds or we need to round up.
         output = vr + ((vr == vm && (!acceptBounds || !vmIsTrailingZeros)) || lastRemovedDigit >= 5);
     }
     else
     {
         // Specialized for the common case (~99.3%). Percentages below are relative to this.
         bool roundUp = false;
         const std::uint64_t vpDiv100 = div100(vp);
         const std::uint64_t vmDiv100 = div100(vm);
         if (vpDiv100 > vmDiv100)
         {
             // Optimization: remove two digits at a time (~86.2%).
             const std::uint64_t vrDiv100 = div100(vr);
             const std::uint32_t vrMod100 = ((std::uint32_t)vr) - 100 * ((std::uint32_t)vrDiv100);
             roundUp = vrMod100 >= 50;
             vr = vrDiv100;
             vp = vpDiv100;
             vm = vmDiv100;
             removed += 2;
         }
         // Loop iterations below (approximately), without optimization above:
         // 0: 0.03%, 1: 13.8%, 2: 70.6%, 3: 14.0%, 4: 1.40%, 5: 0.14%, 6+: 0.02%
         // Loop iterations below (approximately), with optimization above:
         // 0: 70.6%, 1: 27.8%, 2: 1.40%, 3: 0.14%, 4+: 0.02%
         for (;;)
         {
             const std::uint64_t vpDiv10 = div10(vp);
             const std::uint64_t vmDiv10 = div10(vm);
             if (vpDiv10 <= vmDiv10)
                 break;
             const std::uint64_t vrDiv10 = div10(vr);
             const std::uint32_t vrMod10 = ((std::uint32_t)vr) - 10 * ((std::uint32_t)vrDiv10);
             roundUp = vrMod10 >= 5;
             vr = vrDiv10;
             vp = vpDiv10;
             vm = vmDiv10;
             ++removed;
         }
 #ifdef RYU_DEBUG
         printf("%" PRIu64 " roundUp=%s\n", vr, roundUp ? "true" : "false");
         printf("vr is trailing zeros=%s\n", vrIsTrailingZeros ? "true" : "false");
 #endif
         // We need to take vr + 1 if vr is outside bounds or we need to round up.
         output = vr + (vr == vm || roundUp);
     }
     const std::int32_t exp = e10 + removed;
 
 #ifdef RYU_DEBUG
     printf("V+=%" PRIu64 "\nV =%" PRIu64 "\nV-=%" PRIu64 "\n", vp, vr, vm);
     printf("O=%" PRIu64 "\n", output);
     printf("EXP=%d\n", exp);
 #endif
 
     floating_decimal_64 fd;
     fd.exponent = exp;
     fd.mantissa = output;
     return fd;
 }
 
 inline
 int
 to_chars(
     const floating_decimal_64 v,
     const bool sign,
     char* const result)
 {
     // Step 5: Print the decimal representation.
     int index = 0;
     if (sign)
         result[index++] = '-';
 
     std::uint64_t output = v.mantissa;
     std::uint32_t const olength = decimalLength17(output);
 
 #ifdef RYU_DEBUG
     printf("DIGITS=%" PRIu64 "\n", v.mantissa);
     printf("OLEN=%u\n", olength);
     printf("EXP=%u\n", v.exponent + olength);
 #endif
 
     // Print the decimal digits.
     // The following code is equivalent to:
     // for (uint32_t i = 0; i < olength - 1; ++i) {
     //   const uint32_t c = output % 10; output /= 10;
     //   result[index + olength - i] = (char) ('0' + c);
     // }
     // result[index] = '0' + output % 10;
 
     std::uint32_t i = 0;
     // We prefer 32-bit operations, even on 64-bit platforms.
     // We have at most 17 digits, and uint32_t can store 9 digits.
     // If output doesn't fit into uint32_t, we cut off 8 digits,
     // so the rest will fit into uint32_t.
     if ((output >> 32) != 0)
     {
         // Expensive 64-bit division.
         std::uint64_t const q = div1e8(output);
         std::uint32_t output2 = ((std::uint32_t)output) - 100000000 * ((std::uint32_t)q);
         output = q;
 
         const std::uint32_t c = output2 % 10000;
         output2 /= 10000;
         const std::uint32_t d = output2 % 10000;
         const std::uint32_t c0 = (c % 100) << 1;
         const std::uint32_t c1 = (c / 100) << 1;
         const std::uint32_t d0 = (d % 100) << 1;
         const std::uint32_t d1 = (d / 100) << 1;
         std::memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c0, 2);
         std::memcpy(result + index + olength - i - 3, DIGIT_TABLE() + c1, 2);
         std::memcpy(result + index + olength - i - 5, DIGIT_TABLE() + d0, 2);
         std::memcpy(result + index + olength - i - 7, DIGIT_TABLE() + d1, 2);
         i += 8;
     }
     uint32_t output2 = (std::uint32_t)output;
     while (output2 >= 10000)
     {
 #ifdef __clang__ // https://bugs.llvm.org/show_bug.cgi?id=38217
         const uint32_t c = output2 - 10000 * (output2 / 10000);
 #else
         const uint32_t c = output2 % 10000;
 #endif
         output2 /= 10000;
         const uint32_t c0 = (c % 100) << 1;
         const uint32_t c1 = (c / 100) << 1;
         memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c0, 2);
         memcpy(result + index + olength - i - 3, DIGIT_TABLE() + c1, 2);
         i += 4;
     }
     if (output2 >= 100) {
         const uint32_t c = (output2 % 100) << 1;
         output2 /= 100;
         memcpy(result + index + olength - i - 1, DIGIT_TABLE() + c, 2);
         i += 2;
     }
     if (output2 >= 10) {
         const uint32_t c = output2 << 1;
         // We can't use memcpy here: the decimal dot goes between these two digits.
         result[index + olength - i] = DIGIT_TABLE()[c + 1];
         result[index] = DIGIT_TABLE()[c];
     }
     else {
         result[index] = (char)('0' + output2);
     }
 
     // Print decimal point if needed.
     if (olength > 1) {
         result[index + 1] = '.';
         index += olength + 1;
     }
     else {
         ++index;
     }
 
     // Print the exponent.
     result[index++] = 'E';
     int32_t exp = v.exponent + (int32_t)olength - 1;
     if (exp < 0) {
         result[index++] = '-';
         exp = -exp;
     }
 
     if (exp >= 100) {
         const int32_t c = exp % 10;
         memcpy(result + index, DIGIT_TABLE() + 2 * (exp / 10), 2);
         result[index + 2] = (char)('0' + c);
         index += 3;
     }
     else if (exp >= 10) {
         memcpy(result + index, DIGIT_TABLE() + 2 * exp, 2);
         index += 2;
     }
     else {
         result[index++] = (char)('0' + exp);
     }
 
     return index;
 }
 
 static inline bool d2d_small_int(const uint64_t ieeeMantissa, const uint32_t ieeeExponent,
   floating_decimal_64* const v) {
   const uint64_t m2 = (1ull << DOUBLE_MANTISSA_BITS) | ieeeMantissa;
   const int32_t e2 = (int32_t) ieeeExponent - DOUBLE_BIAS - DOUBLE_MANTISSA_BITS;
 
   if (e2 > 0) {
     // f = m2 * 2^e2 >= 2^53 is an integer.
     // Ignore this case for now.
     return false;
   }
 
   if (e2 < -52) {
     // f < 1.
     return false;
   }
 
   // Since 2^52 <= m2 < 2^53 and 0 <= -e2 <= 52: 1 <= f = m2 / 2^-e2 < 2^53.
   // Test if the lower -e2 bits of the significand are 0, i.e. whether the fraction is 0.
   const uint64_t mask = (1ull << -e2) - 1;
   const uint64_t fraction = m2 & mask;
   if (fraction != 0) {
     return false;
   }
 
   // f is an integer in the range [1, 2^53).
   // Note: mantissa might contain trailing (decimal) 0's.
   // Note: since 2^53 < 10^16, there is no need to adjust decimalLength17().
   v->mantissa = m2 >> -e2;
   v->exponent = 0;
   return true;
 }
 
 } // detail
 
 int
 d2s_buffered_n(
     double f,
     char* result,
     bool allow_infinity_and_nan) noexcept
 {
     using namespace detail;
     // Step 1: Decode the floating-point number, and unify normalized and subnormal cases.
     std::uint64_t const bits = double_to_bits(f);
 
 #ifdef RYU_DEBUG
     printf("IN=");
     for (std::int32_t bit = 63; bit >= 0; --bit) {
         printf("%d", (int)((bits >> bit) & 1));
     }
     printf("\n");
 #endif
 
     // Decode bits into sign, mantissa, and exponent.
     const bool ieeeSign = ((bits >> (DOUBLE_MANTISSA_BITS + DOUBLE_EXPONENT_BITS)) & 1) != 0;
     const std::uint64_t ieeeMantissa = bits & ((1ull << DOUBLE_MANTISSA_BITS) - 1);
     const std::uint32_t ieeeExponent = (std::uint32_t)((bits >> DOUBLE_MANTISSA_BITS) & ((1u << DOUBLE_EXPONENT_BITS) - 1));
     // Case distinction; exit early for the easy cases.
     if (ieeeExponent == ((1u << DOUBLE_EXPONENT_BITS) - 1u) || (ieeeExponent == 0 && ieeeMantissa == 0)) {
         // We changed how special numbers are output by default
         if (allow_infinity_and_nan)
             return copy_special_str(result, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
         else
             return copy_special_str_conforming(result, ieeeSign, ieeeExponent != 0, ieeeMantissa != 0);
 
     }
 
     floating_decimal_64 v;
     const bool isSmallInt = d2d_small_int(ieeeMantissa, ieeeExponent, &v);
     if (isSmallInt) {
         // For small integers in the range [1, 2^53), v.mantissa might contain trailing (decimal) zeros.
         // For scientific notation we need to move these zeros into the exponent.
         // (This is not needed for fixed-point notation, so it might be beneficial to trim
         // trailing zeros in to_chars only if needed - once fixed-point notation output is implemented.)
         for (;;) {
             std::uint64_t const q = div10(v.mantissa);
             std::uint32_t const r = ((std::uint32_t) v.mantissa) - 10 * ((std::uint32_t) q);
             if (r != 0)
                 break;
             v.mantissa = q;
             ++v.exponent;
         }
     }
     else {
         v = d2d(ieeeMantissa, ieeeExponent);
     }
 
     return to_chars(v, ieeeSign, result);
 }
 
 } // ryu
 
 } // detail
 } // namespace json
 } // namespace boost
 
 #endif

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