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diff --git a/include/jsoncons_ext/bson/bson_decimal128.hpp b/include/jsoncons_ext/bson/bson_decimal128.hpp
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+++ b/include/jsoncons_ext/bson/bson_decimal128.hpp
@@ -0,0 +1,865 @@
+#ifndef JSONCONS_BSON_BSON_DECIMAL128_HPP
+#define JSONCONS_BSON_BSON_DECIMAL128_HPP
+
+/*
+ *  Implements decimal128_to_chars and decimal128_from_chars
+ *  
+ *  Based on the libjson functions bson_decimal128_to_string
+ *  and bson_decimal128_from_string_w_len, available at
+ *  https://github.com/mongodb/mongo-c-driver/blob/master/src/libbson/src/bson/bson-decimal128.h
+ *  and https://github.com/mongodb/mongo-c-driver/blob/master/src/libbson/src/bson/bson-decimal128.c
+ *  
+*/
+
+/*
+ * Copyright 2015 MongoDB, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <cstring>
+#include <ctype.h>
+#include <system_error>
+#include <algorithm>
+#include <jsoncons/config/jsoncons_config.hpp>
+
+namespace jsoncons { namespace bson {
+
+    struct decimal128_to_chars_result 
+    {
+        char* ptr;
+        std::errc ec;
+    };
+
+    struct decimal128_from_chars_result 
+    {
+        const char* ptr;
+        std::errc ec;
+    };
+
+/**
+ * BSON_DECIMAL128_STRING:
+ *
+ * The length of a decimal128 string (with null terminator).
+ *
+ * 1  for the sign
+ * 35 for digits and radix
+ * 2  for exponent indicator and sign
+ * 4  for exponent digits
+ */
+#define BSON_DECIMAL128_STRING 43
+
+    struct TP1 
+    { 
+        uint64_t low; 
+        uint64_t high; 
+
+        constexpr TP1() : low(0), high(0) {}
+        constexpr TP1(uint64_t hi, uint64_t lo) : low(lo), high(hi) {}
+    };
+    struct TP2 
+    { 
+        uint64_t high; 
+        uint64_t low; 
+
+        constexpr TP2() : high(0), low(0) {}
+        constexpr TP2(uint64_t hi, uint64_t lo) : high(hi), low(lo) {}
+    };
+
+    typedef std::conditional<
+        jsoncons::endian::native == jsoncons::endian::little,
+        TP1,
+        TP2
+    >::type decimal128_t;
+
+    inline
+    bool operator==(const decimal128_t& lhs, const decimal128_t& rhs)
+    {
+       return lhs.high == rhs.high && lhs.low == rhs.low;
+    }   
+
+    inline
+    bool operator!=(const decimal128_t& lhs, const decimal128_t& rhs)
+    {
+       return !(lhs == rhs);
+    }   
+
+    struct decimal128_limits
+    {
+        // The length of a decimal128 string (without null terminator).
+        //
+        // 1  for the sign
+        // 35 for digits and radix
+        // 2  for exponent indicator and sign
+        // 4  for exponent digits
+        static constexpr int buf_size = 42;  
+        static constexpr int exponent_max = 6111;
+        static constexpr int exponent_min = -6176;
+        static constexpr int exponent_bias = 6176;
+        static constexpr int max_digits = 34;
+
+        static constexpr decimal128_t nan() {return decimal128_t(0x7c00000000000000ull, 0);}
+        static constexpr decimal128_t infinity() {return decimal128_t(0x7800000000000000ull, 0);}
+        static constexpr decimal128_t neg_infinity() {return decimal128_t(0x7800000000000000ull + 0x8000000000000000ull, 0);}
+    };
+
+    inline
+    bool is_nan(decimal128_t dec) { return dec == decimal128_limits::nan(); }
+
+    inline
+    bool is_inf(decimal128_t dec) { return dec == decimal128_limits::infinity(); }
+
+    inline
+    bool is_neg_inf(decimal128_t dec) { return dec == decimal128_limits::neg_infinity(); }
+
+    /**
+     * bson_uint128_t:
+     *
+     * This struct represents a 128 bit integer.
+     */
+    typedef struct {
+       uint32_t parts[4]; /* 32-bit words stored high to low. */
+    } bson_uint128_t;
+
+    typedef struct {
+       uint64_t high, low;
+    } bson_uint128_6464_t;
+
+    namespace detail {
+    
+        /**
+         *------------------------------------------------------------------------------
+         *
+         * bson_uint128_divide1B --
+         *
+         *    This function divides a #bson_uint128_t by 1000000000 (1 billion) and
+         *    computes the quotient and remainder.
+         *
+         *    The remainder will contain 9 decimal digits for conversion to string.
+         *
+         * @value     The #bson_uint128_t operand.
+         * @quotient  A pointer to store the #bson_uint128_t quotient.
+         * @rem       A pointer to store the #uint64_t remainder.
+         *
+         * Returns:
+         *    The quotient at @quotient and the remainder at @rem.
+         *
+         * Side effects:
+         *    None.
+         *
+         *------------------------------------------------------------------------------
+         */
+
+        inline
+        void bson_uint128_divide1B (bson_uint128_t value,     /* IN */
+                                     bson_uint128_t *quotient, /* OUT */
+                                     uint32_t *rem)             /* OUT */
+        {
+            const uint32_t DIVISOR = 1000 * 1000 * 1000;
+            uint64_t _rem = 0;
+            int i = 0;
+            
+            if (!value.parts[0] && !value.parts[1] && !value.parts[2] &&
+                !value.parts[3]) {
+               *quotient = value;
+               *rem = 0;
+               return;
+            }
+            
+            for (i = 0; i <= 3; i++) {
+               _rem <<= 32; /* Adjust remainder to match value of next dividend */
+               _rem += value.parts[i]; /* Add the divided to _rem */
+               value.parts[i] = (uint32_t) (_rem / DIVISOR);
+               _rem %= DIVISOR; /* Store the remainder */
+            }
+            
+            *quotient = value;
+            *rem = (uint32_t) _rem;
+        }
+
+        /**
+         *-------------------------------------------------------------------------
+         *
+         * mul64x64 --
+         *
+         *    This function multiplies two &uint64_t into a &bson_uint128_6464_t.
+         *
+         * Returns:
+         *    The product of @left and @right.
+         *
+         * Side Effects:
+         *    None.
+         *
+         *-------------------------------------------------------------------------
+         */
+
+        inline
+        void mul_64x64 (uint64_t left,                 /* IN */
+                        uint64_t right,                /* IN */
+                        bson_uint128_6464_t *product) /* OUT */
+        {
+            uint64_t left_high, left_low, right_high, right_low, product_high,
+               product_mid, product_mid2, product_low;
+            bson_uint128_6464_t rt = {0,0};
+ 
+            if (!left && !right) {
+               *product = rt;
+               return;
+            }
+ 
+            left_high = left >> 32;
+            left_low = (uint32_t) left;
+            right_high = right >> 32;
+            right_low = (uint32_t) right;
+ 
+            product_high = left_high * right_high;
+            product_mid = left_high * right_low;
+            product_mid2 = left_low * right_high;
+            product_low = left_low * right_low;
+ 
+            product_high += product_mid >> 32;
+            product_mid = (uint32_t) product_mid + product_mid2 + (product_low >> 32);
+ 
+            product_high = product_high + (product_mid >> 32);
+            product_low = (product_mid << 32) + (uint32_t) product_low;
+ 
+            rt.high = product_high;
+            rt.low = product_low;
+            *product = rt;
+        }
+
+        /**
+         *------------------------------------------------------------------------------
+         *
+         * dec128_tolower --
+         *
+         *    This function converts the ASCII character @c to lowercase.  It is locale
+         *    insensitive (unlike the stdlib tolower).
+         *
+         * Returns:
+         *    The lowercased character.
+         */
+
+        inline
+        char dec128_tolower (char c)
+        {
+           if (isupper (c)) {
+              c += 32;
+           }
+
+           return c;
+        }
+
+        /**
+         *------------------------------------------------------------------------------
+         *
+         * dec128_istreq --
+         *
+         *    This function compares the null-terminated *ASCII* strings @a and @b
+         *    for case-insensitive equality.
+         *
+         * Returns:
+         *    true if the strings are equal, false otherwise.
+         */
+
+        inline
+        bool dec128_istreq (const char* a, const char* lasta,
+                            const char* b, const char* lastb)
+        {
+            while (!(a == lasta && b == lastb)) 
+            {
+               // strings are different lengths
+               if (a == lasta || b == lastb) 
+               {
+                  return false;
+               }
+         
+               if (dec128_tolower (*a) != dec128_tolower (*b)) {
+                  return false;
+               }
+         
+               a++;
+               b++;
+            }
+         
+            return true;
+        }
+
+    } // namespace detail
+
+
+    /**
+     *------------------------------------------------------------------------------
+     *
+     * decimal128_to_chars --
+     *
+     *    This function converts a BID formatted decimal128 value to string,
+     *    accepting a &decimal128_t as @dec.  The string is stored at @str.
+     *
+     * @dec : The BID formatted decimal to convert.
+     * @str : The output decimal128 string. At least %BSON_DECIMAL128_STRING
+     *characters.
+     *
+     * Returns:
+     *    None.
+     *
+     * Side effects:
+     *    None.
+     *
+     *------------------------------------------------------------------------------
+     */
+
+    inline
+    decimal128_to_chars_result decimal128_to_chars(char* first, char* last, const decimal128_t& dec)
+    {
+        const std::string bson_decimal128_inf = "Infinity";
+        const std::string bson_decimal128_nan = "NaN";
+
+        const uint32_t combination_mask = 0x1f;   /* Extract least significant 5 bits */
+        const uint32_t exponent_mask = 0x3fff;    /* Extract least significant 14 bits */
+        const uint32_t combination_infinity = 30; /* Value of combination field for Inf */
+        const uint32_t combination_nan = 31;      /* Value of combination field for NaN */
+        const uint32_t exponent_bias = 6176;      /* decimal128 exponent bias */
+
+        char* str_out = first;      /* output pointer in string */
+        char significand_str[35]; /* decoded significand digits */
+
+        /* Note: bits in this routine are referred to starting at 0, */
+        /* from the sign bit, towards the coefficient. */
+        uint32_t high;                   /* bits 0 - 31 */
+        uint32_t midh;                   /* bits 32 - 63 */
+        uint32_t midl;                   /* bits 64 - 95 */
+        uint32_t low;                    /* bits 96 - 127 */
+        uint32_t combination;            /* bits 1 - 5 */
+        uint32_t biased_exponent;        /* decoded biased exponent (14 bits) */
+        uint32_t significand_digits = 0; /* the number of significand digits */
+        uint32_t significand[36] = {0};  /* the base-10 digits in the significand */
+        uint32_t *significand_read = significand; /* read pointer into significand */
+        int32_t exponent;                         /* unbiased exponent */
+        int32_t scientific_exponent; /* the exponent if scientific notation is
+                                      * used */
+        bool is_zero = false;        /* true if the number is zero */
+ 
+        uint8_t significand_msb; /* the most signifcant significand bits (50-46) */
+        bson_uint128_t
+           significand128; /* temporary storage for significand decoding */
+ 
+        memset (significand_str, 0, sizeof (significand_str));
+ 
+        if ((int64_t) dec.high < 0) { /* negative */
+           *(str_out++) = '-';
+        }
+ 
+        low = (uint32_t) dec.low, midl = (uint32_t) (dec.low >> 32),
+        midh = (uint32_t) dec.high, high = (uint32_t) (dec.high >> 32);
+ 
+        /* Decode combination field and exponent */
+        combination = (high >> 26) & combination_mask;
+ 
+        if (JSONCONS_UNLIKELY ((combination >> 3) == 3)) {
+           /* Check for 'special' values */
+           if (combination == combination_infinity) { /* Infinity */
+               if (last-str_out >= static_cast<ptrdiff_t >(bson_decimal128_inf.size())) 
+               {
+                   std::memcpy(str_out, bson_decimal128_inf.data(), bson_decimal128_inf.size());
+                   str_out += bson_decimal128_inf.size();
+               }
+               *str_out = 0;
+              //strcpy_s (str_out, last-str_out, bson_decimal128_inf.c_str());
+              return decimal128_to_chars_result{str_out, std::errc()};
+           } else if (combination == combination_nan) { /* NaN */
+               /* first, not str_out, to erase the sign */
+               str_out = first;
+               if (last-str_out >= static_cast<ptrdiff_t >(bson_decimal128_nan.size())) 
+               {
+                   std::memcpy(str_out, bson_decimal128_nan.data(), bson_decimal128_nan.size());
+                   str_out += bson_decimal128_nan.size();
+               }
+               *str_out = 0;
+              //strcpy_s (first, last-first, bson_decimal128_nan.c_str());
+              /* we don't care about the NaN payload. */
+               return decimal128_to_chars_result{str_out, std::errc()};
+           } else {
+              biased_exponent = (high >> 15) & exponent_mask;
+              significand_msb = 0x8 + ((high >> 14) & 0x1);
+           }
+        } else {
+           significand_msb = (high >> 14) & 0x7;
+           biased_exponent = (high >> 17) & exponent_mask;
+        }
+ 
+        exponent = biased_exponent - exponent_bias;
+        /* Create string of significand digits */
+ 
+        /* Convert the 114-bit binary number represented by */
+        /* (high, midh, midl, low) to at most 34 decimal */
+        /* digits through modulo and division. */
+        significand128.parts[0] = (high & 0x3fff) + ((significand_msb & 0xf) << 14);
+        significand128.parts[1] = midh;
+        significand128.parts[2] = midl;
+        significand128.parts[3] = low;
+ 
+        if (significand128.parts[0] == 0 && significand128.parts[1] == 0 &&
+            significand128.parts[2] == 0 && significand128.parts[3] == 0) {
+           is_zero = true;
+        } else if (significand128.parts[0] >= (1 << 17)) {
+           /* The significand is non-canonical or zero.
+            * In order to preserve compatibility with the densely packed decimal
+            * format, the maximum value for the significand of decimal128 is
+            * 1e34 - 1.  If the value is greater than 1e34 - 1, the IEEE 754
+            * standard dictates that the significand is interpreted as zero.
+            */
+           is_zero = true;
+        } else {
+           for (int k = 3; k >= 0; k--) {
+              uint32_t least_digits = 0;
+              detail::bson_uint128_divide1B (
+                 significand128, &significand128, &least_digits);
+ 
+              /* We now have the 9 least significant digits (in base 2). */
+              /* Convert and output to string. */
+              if (!least_digits) {
+                 continue;
+              }
+ 
+              for (int j = 8; j >= 0; j--) {
+                 significand[k * 9 + j] = least_digits % 10;
+                 least_digits /= 10;
+              }
+           }
+        }
+ 
+        /* Output format options: */
+        /* Scientific - [-]d.dddE(+/-)dd or [-]dE(+/-)dd */
+        /* Regular    - ddd.ddd */
+ 
+        if (is_zero) {
+           significand_digits = 1;
+           *significand_read = 0;
+        } else {
+           significand_digits = 36;
+           while (!(*significand_read)) {
+              significand_digits--;
+              significand_read++;
+           }
+        }
+ 
+        scientific_exponent = significand_digits - 1 + exponent;
+ 
+        /* The scientific exponent checks are dictated by the string conversion
+         * specification and are somewhat arbitrary cutoffs.
+         *
+         * We must check exponent > 0, because if this is the case, the number
+         * has trailing zeros.  However, we *cannot* output these trailing zeros,
+         * because doing so would change the precision of the value, and would
+         * change stored data if the string converted number is round tripped.
+         */
+        if (scientific_exponent < -6 || exponent > 0) {
+           /* Scientific format */
+           *(str_out++) = char(*(significand_read++)) + '0';
+           significand_digits--;
+ 
+           if (significand_digits) {
+              *(str_out++) = '.';
+           }
+ 
+           for (std::size_t i = 0; i < significand_digits && (str_out - first) < 36; i++) {
+              *(str_out++) = char(*(significand_read++)) + '0';
+           }
+           /* Exponent */
+           *(str_out++) = 'E';
+
+           std::string s;
+           if (scientific_exponent >= 0) {
+               s.push_back('+');
+           }
+           jsoncons::detail::from_integer(scientific_exponent, s);
+           if (str_out + s.size() < last) 
+           {
+               std::memcpy(str_out, s.data(), s.size());
+           }
+           else
+           {
+               return decimal128_to_chars_result{str_out, std::errc::value_too_large};
+           }
+           str_out += s.size();
+        } else {
+           /* Regular format with no decimal place */
+           if (exponent >= 0) {
+              for (std::size_t i = 0; i < significand_digits && (str_out - first) < 36; i++) {
+                 *(str_out++) = char(*(significand_read++)) + '0';
+              }
+           } else {
+              int32_t radix_position = significand_digits + exponent;
+ 
+              if (radix_position > 0) { /* non-zero digits before radix */
+                 for (int32_t i = 0;
+                      i < radix_position && (str_out < last);
+                      i++) {
+                    *(str_out++) = char(*(significand_read++)) + '0';
+                 }
+              } else { /* leading zero before radix point */
+                 *(str_out++) = '0';
+              }
+ 
+              *(str_out++) = '.';
+              while (radix_position++ < 0) { /* add leading zeros after radix */
+                 *(str_out++) = '0';
+              }
+ 
+              for (std::size_t i = 0;
+                   (i < significand_digits - (std::max) (radix_position - 1, 0)) &&
+                   (str_out < last);
+                   i++) {
+                 *(str_out++) = char(*(significand_read++)) + '0';
+              }
+           }
+        }
+        return decimal128_to_chars_result{str_out, std::errc()};
+    }
+
+
+
+    /**
+     *------------------------------------------------------------------------------
+     *
+     * bson_decimal128_from_string_w_len --
+     *
+     *    This function converts @string in the format [+-]ddd[.]ddd[E][+-]dddd to
+     *    decimal128.  Out of range values are converted to +/-Infinity.  Invalid
+     *    strings are converted to NaN. @len is the length of the string, or -1
+     *    meaning the string is null-terminated.
+     *
+     *    If more digits are provided than the available precision allows,
+     *    round to the nearest expressable decimal128 with ties going to even will
+     *    occur.
+     *
+     *    Note: @string must be ASCII only!
+     *
+     * Returns:
+     *    true on success, or false on failure. @dec will be NaN if @str was invalid
+     *    The &decimal128_t converted from @string at @dec.
+     *
+     * Side effects:
+     *    None.
+     *
+     *------------------------------------------------------------------------------
+     */
+
+    inline
+    decimal128_from_chars_result decimal128_from_chars(const char* first, const char* last, decimal128_t& dec) 
+    {
+        const string_view inf_str = "inf";
+        const string_view infinity_str = "infinity";
+        const string_view nan_str = "nan";
+
+        ptrdiff_t len = last - first;
+
+        bson_uint128_6464_t significand = {0,0};
+ 
+        const char* str_read = first; /* Read pointer for consuming str. */
+ 
+        /* Parsing state tracking */
+        bool is_negative = false;
+        bool saw_radix = false;
+        bool includes_sign = false; /* True if the input first contains a sign. */
+        bool found_nonzero = false;
+ 
+        size_t significant_digits = 0; /* Total number of significant digits
+                                        * (no leading or trailing zero) */
+        size_t ndigits_read = 0;       /* Total number of significand digits read */
+        size_t ndigits = 0;        /* Total number of digits (no leading zeros) */
+        size_t radix_position = 0; /* The number of the digits after radix */
+        size_t first_nonzero = 0;  /* The index of the first non-zero in *str* */
+ 
+        uint16_t digits[decimal128_limits::max_digits] = {0};
+        uint16_t ndigits_stored = 0;      /* The number of digits in digits */
+        uint16_t *digits_insert = digits; /* Insertion pointer for digits */
+        size_t first_digit = 0;           /* The index of the first non-zero digit */
+        size_t last_digit = 0;            /* The index of the last digit */
+ 
+        int32_t exponent = 0;
+        uint64_t significand_high = 0; /* The high 17 digits of the significand */
+        uint64_t significand_low = 0;  /* The low 17 digits of the significand */
+        uint16_t biased_exponent = 0;  /* The biased exponent */
+ 
+        dec.high = 0;
+        dec.low = 0;
+ 
+        if (*str_read == '+' || *str_read == '-') {
+           is_negative = *(str_read++) == '-';
+           includes_sign = true;
+        }
+
+        /* Check for Infinity or NaN */
+        if (!isdigit (*str_read) && *str_read != '.') {
+           if (detail::dec128_istreq (str_read, last, inf_str.data(), inf_str.data()+inf_str.length()) ||
+               detail::dec128_istreq (str_read, last, infinity_str.data(), infinity_str.data()+infinity_str.length())) 
+           {
+               dec = is_negative ? decimal128_limits::neg_infinity() : decimal128_limits::infinity();
+              return decimal128_from_chars_result{str_read,std::errc()};
+           } else if (detail::dec128_istreq (str_read, last, nan_str.data(), nan_str.data()+nan_str.length())) {
+              dec = decimal128_limits::nan();
+              return decimal128_from_chars_result{str_read,std::errc()};
+           }
+ 
+           dec = decimal128_limits::nan();
+           return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+        }
+ 
+        /* Read digits */
+        while (((isdigit (*str_read) || *str_read == '.')) &&
+               (len == -1 || str_read < first + len)) {
+           if (*str_read == '.') {
+              if (saw_radix) {
+                 dec = decimal128_limits::nan();
+                 return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+              }
+ 
+              saw_radix = true;
+              str_read++;
+              continue;
+           }
+ 
+           if (ndigits_stored < 34) {
+              if (*str_read != '0' || found_nonzero) {
+                 if (!found_nonzero) {
+                    first_nonzero = ndigits_read;
+                 }
+ 
+                 found_nonzero = true;
+                 *(digits_insert++) = *(str_read) - '0'; /* Only store 34 digits */
+                 ndigits_stored++;
+              }
+           }
+ 
+           if (found_nonzero) {
+              ndigits++;
+           }
+ 
+           if (saw_radix) {
+              radix_position++;
+           }
+ 
+           ndigits_read++;
+           str_read++;
+        }
+ 
+        if (saw_radix && !ndigits_read) {
+           dec = decimal128_limits::nan();
+           return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+        }
+ 
+        /* Read exponent if exists */
+        if (*str_read == 'e' || *str_read == 'E') {
+           ++str_read;
+           if (*str_read == '+') {
+               ++str_read;
+           }
+           auto result = jsoncons::detail::to_integer(str_read, last - str_read, exponent);
+           if (result.ec != jsoncons::detail::to_integer_errc()) 
+           {
+               dec = decimal128_limits::nan();
+               return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+           }
+           str_read = result.ptr;
+        }
+
+        if ((len == -1 || str_read < first + len) && *str_read) {
+           dec = decimal128_limits::nan();
+           return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+        }
+ 
+        /* Done reading input. */
+        /* Find first non-zero digit in digits */
+        first_digit = 0;
+ 
+        if (!ndigits_stored) { /* value is zero */
+           first_digit = 0;
+           last_digit = 0;
+           digits[0] = 0;
+           ndigits = 1;
+           ndigits_stored = 1;
+           significant_digits = 0;
+        } else {
+           last_digit = ndigits_stored - 1;
+           significant_digits = ndigits;
+           /* Mark trailing zeros as non-significant */
+           while (first[first_nonzero + significant_digits - 1 + includes_sign +
+                         saw_radix] == '0') {
+              significant_digits--;
+           }
+        }
+ 
+ 
+        /* Normalization of exponent */
+        /* Correct exponent based on radix position, and shift significand as needed
+         */
+        /* to represent user input */
+ 
+        /* Overflow prevention */
+        if (exponent <= static_cast<int32_t>(radix_position) && static_cast<int32_t>(radix_position) - exponent > (1 << 14)) {
+           exponent = decimal128_limits::exponent_min;
+        } else {
+           exponent -= static_cast<int32_t>(radix_position);
+        }
+ 
+        /* Attempt to normalize the exponent */
+        while (exponent > decimal128_limits::exponent_max) {
+           /* Shift exponent to significand and decrease */
+           last_digit++;
+ 
+           if (last_digit - first_digit > decimal128_limits::max_digits) {
+              /* The exponent is too great to shift into the significand. */
+              if (significant_digits == 0) {
+                 /* Value is zero, we are allowed to clamp the exponent. */
+                 exponent = decimal128_limits::exponent_max;
+                 break;
+              }
+ 
+              /* Overflow is not permitted, error. */
+              dec = decimal128_limits::nan();
+              return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+           }
+ 
+           exponent--;
+        }
+ 
+        while (exponent < decimal128_limits::exponent_min || ndigits_stored < ndigits) {
+           /* Shift last digit */
+           if (last_digit == 0) {
+              /* underflow is not allowed, but zero clamping is */
+              if (significant_digits == 0) {
+                 exponent = decimal128_limits::exponent_min;
+                 break;
+              }
+ 
+              dec = decimal128_limits::nan();
+              return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+           }
+ 
+           if (ndigits_stored < ndigits) {
+              if (first[ndigits - 1 + includes_sign + saw_radix] - '0' != 0 &&
+                  significant_digits != 0) {
+                 dec = decimal128_limits::nan();
+                 return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+              }
+ 
+              ndigits--; /* adjust to match digits not stored */
+           } else {
+              if (digits[last_digit] != 0) {
+                 /* Inexact rounding is not allowed. */
+                 dec = decimal128_limits::nan();
+                 return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+              }
+ 
+ 
+              last_digit--; /* adjust to round */
+           }
+ 
+           if (exponent < decimal128_limits::exponent_max) {
+              exponent++;
+           } else {
+              dec = decimal128_limits::nan();
+              return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+           }
+        }
+ 
+        /* Round */
+        /* We've normalized the exponent, but might still need to round. */
+        if (last_digit - first_digit + 1 < significant_digits) {
+           uint8_t round_digit;
+ 
+           /* There are non-zero digits after last_digit that need rounding. */
+           /* We round to nearest, ties to even */
+           round_digit =
+              first[first_nonzero + last_digit + includes_sign + saw_radix + 1] -
+              '0';
+ 
+           if (round_digit != 0) {
+              /* Inexact (non-zero) rounding is not allowed */
+              dec = decimal128_limits::nan();
+              return decimal128_from_chars_result{str_read,std::errc::invalid_argument};
+           }
+        }
+ 
+        /* Encode significand */
+        significand_high = 0,   /* The high 17 digits of the significand */
+           significand_low = 0; /* The low 17 digits of the significand */
+ 
+        if (significant_digits == 0) { /* read a zero */
+           significand_high = 0;
+           significand_low = 0;
+        } else if (last_digit - first_digit < 17) {
+           size_t d_idx = first_digit;
+           significand_low = digits[d_idx++];
+ 
+           for (; d_idx <= last_digit; d_idx++) {
+              significand_low *= 10;
+              significand_low += digits[d_idx];
+              significand_high = 0;
+           }
+        } else {
+           size_t d_idx = first_digit;
+           significand_high = digits[d_idx++];
+ 
+           for (; d_idx <= last_digit - 17; d_idx++) {
+              significand_high *= 10;
+              significand_high += digits[d_idx];
+           }
+ 
+           significand_low = digits[d_idx++];
+ 
+           for (; d_idx <= last_digit; d_idx++) {
+              significand_low *= 10;
+              significand_low += digits[d_idx];
+           }
+        }
+ 
+        detail::mul_64x64 (significand_high, 100000000000000000ull, &significand);
+        significand.low += significand_low;
+ 
+        if (significand.low < significand_low) {
+           significand.high += 1;
+        }
+ 
+ 
+        biased_exponent = static_cast<uint16_t>(exponent + static_cast<int32_t>(decimal128_limits::exponent_bias));
+ 
+        /* Encode combination, exponent, and significand. */
+        if ((significand.high >> 49) & 1) {
+           /* Encode '11' into bits 1 to 3 */
+           dec.high |= (0x3ull << 61);
+           dec.high |= (biased_exponent & 0x3fffull) << 47;
+           dec.high |= significand.high & 0x7fffffffffffull;
+        } else {
+           dec.high |= (biased_exponent & 0x3fffull) << 49;
+           dec.high |= significand.high & 0x1ffffffffffffull;
+        }
+ 
+        dec.low = significand.low;
+ 
+        /* Encode sign */
+        if (is_negative) {
+           dec.high |= 0x8000000000000000ull;
+        }
+ 
+        return decimal128_from_chars_result{str_read,std::errc()};
+    }
+
+} // namespace bson
+} // namespace jsoncons
+
+#endif