ceph/src/boost/boost/json/detail/ryu/detail/common.hpp

   1 // Copyright 2018 Ulf Adams
   2 //
   3 // The contents of this file may be used under the terms of the Apache License,
   4 // Version 2.0.
   5 //
   6 //    (See accompanying file LICENSE-Apache or copy at
   7 //     http://www.apache.org/licenses/LICENSE-2.0)
   8 //
   9 // Alternatively, the contents of this file may be used under the terms of
  10 // the Boost Software License, Version 1.0.
  11 //    (See accompanying file LICENSE-Boost or copy at
  12 //     https://www.boost.org/LICENSE_1_0.txt)
  13 //
  14 // Unless required by applicable law or agreed to in writing, this software
  15 // is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  16 // KIND, either express or implied.
  17
  18 /*
  19     This is a derivative work
  20 */
  21
  22 #ifndef BOOST_JSON_DETAIL_RYU_DETAIL_COMMON_HPP
  23 #define BOOST_JSON_DETAIL_RYU_DETAIL_COMMON_HPP
  24
  25 #include <boost/json/detail/config.hpp>
  26 #include <string.h>
  27
  28 BOOST_JSON_NS_BEGIN
  29 namespace detail {
  30
  31 namespace ryu {
  32 namespace detail {
  33
  34 constexpr int DOUBLE_MANTISSA_BITS = 52;
  35 constexpr int DOUBLE_EXPONENT_BITS = 11;
  36 constexpr int DOUBLE_BIAS = 1023;
  37
  38 #if defined(_M_IX86) || defined(_M_ARM)
  39 #define BOOST_JSON_RYU_32_BIT_PLATFORM
  40 #endif
  41
  42 inline uint32_t decimalLength9(const uint32_t v) {
  43   // Function precondition: v is not a 10-digit number.
  44   // (f2s: 9 digits are sufficient for round-tripping.)
  45   // (d2fixed: We print 9-digit blocks.)
  46   BOOST_ASSERT(v < 1000000000);
  47   if (v >= 100000000) { return 9; }
  48   if (v >= 10000000) { return 8; }
  49   if (v >= 1000000) { return 7; }
  50   if (v >= 100000) { return 6; }
  51   if (v >= 10000) { return 5; }
  52   if (v >= 1000) { return 4; }
  53   if (v >= 100) { return 3; }
  54   if (v >= 10) { return 2; }
  55   return 1;
  56 }
  57
  58 // Returns e == 0 ? 1 : ceil(log_2(5^e)).
  59 inline int32_t pow5bits(const int32_t e) {
  60   // This approximation works up to the point that the multiplication overflows at e = 3529.
  61   // If the multiplication were done in 64 bits, it would fail at 5^4004 which is just greater
  62   // than 2^9297.
  63   BOOST_ASSERT(e >= 0);
  64   BOOST_ASSERT(e <= 3528);
  65   return (int32_t) (((((uint32_t) e) * 1217359) >> 19) + 1);
  66 }
  67
  68 // Returns floor(log_10(2^e)).
  69 inline uint32_t log10Pow2(const int32_t e) {
  70   // The first value this approximation fails for is 2^1651 which is just greater than 10^297.
  71   BOOST_ASSERT(e >= 0);
  72   BOOST_ASSERT(e <= 1650);
  73   return (((uint32_t) e) * 78913) >> 18;
  74 }
  75
  76 // Returns floor(log_10(5^e)).
  77 inline uint32_t log10Pow5(const int32_t e) {
  78   // The first value this approximation fails for is 5^2621 which is just greater than 10^1832.
  79   BOOST_ASSERT(e >= 0);
  80   BOOST_ASSERT(e <= 2620);
  81   return (((uint32_t) e) * 732923) >> 20;
  82 }
  83
  84 inline int copy_special_str(char * const result, const bool sign, const bool exponent, const bool mantissa) {
  85   if (mantissa) {
  86     memcpy(result, "NaN", 3);
  87     return 3;
  88   }
  89   if (sign) {
  90     result[0] = '-';
  91   }
  92   if (exponent) {
  93     memcpy(result + sign, "Infinity", 8);
  94     return sign + 8;
  95   }
  96   memcpy(result + sign, "0E0", 3);
  97   return sign + 3;
  98 }
  99
 100 inline uint32_t float_to_bits(const float f) {
 101   uint32_t bits = 0;
 102   memcpy(&bits, &f, sizeof(float));
 103   return bits;
 104 }
 105
 106 inline uint64_t double_to_bits(const double d) {
 107   uint64_t bits = 0;
 108   memcpy(&bits, &d, sizeof(double));
 109   return bits;
 110 }
 111
 112 } // detail
 113 } // ryu
 114
 115 } // detail
 116 BOOST_JSON_NS_END
 117
 118 #endif