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Address review: one powers-of-ten table, literal sizes from the type

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- dtoa_impl::powers_of_ten() (10^0 to 10^19, one entry per line)
  replaces powers_of_ten_16() and the table of int_pow10()
- put_literal() takes the length of a string literal from its type
- small_stack holds the heap vector by reference
- the growth step of the output buffer is written in hex

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-20 10:09:42 +02:00
1 parent aa9f5ff2c8
commit 2020807e85
6 files changed
+95 -103
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single_include/nlohmann/json.hpp
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+26 -8
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@@ -28382,14 +28382,32 @@ inline char* write_shortest(char* first, const zmij::shortest_decimal d) noexcep
return end + (three ? 5 : 4);
}
/// the powers of ten up to 10^16
inline const std::array<std::uint64_t, 17>& powers_of_ten_16() noexcept
/// the powers of ten up to 10^19 (all that fit in std::uint64_t)
inline const std::array<std::uint64_t, 20>& powers_of_ten() noexcept
{
static const std::array<std::uint64_t, 17> powers =
static const std::array<std::uint64_t, 20> powers =
{
{
1u, 10u, 100u, 1000u, 10000u, 100000u, 1000000u, 10000000u, 100000000u, 1000000000u, 10000000000u,
100000000000u, 1000000000000u, 10000000000000u, 100000000000000u, 1000000000000000u, 10000000000000000u
1u,
10u,
100u,
1000u,
10000u,
100000u,
1000000u,
10000000u,
100000000u,
1000000000u,
10000000000u,
100000000000u,
1000000000000u,
10000000000000u,
100000000000000u,
1000000000000000u,
10000000000000000u,
100000000000000000u,
1000000000000000000u,
10000000000000000000u
}
};
return powers;
@@ -28407,9 +28425,9 @@ JSON_HEDLEY_NON_NULL(1)
JSON_HEDLEY_RETURNS_NON_NULL
inline char* write_short_decimal(char* first, std::uint64_t digits, int count, int exp) noexcept
{
JSON_ASSERT(digits >= powers_of_ten_16()[static_cast<std::size_t>(count - 1)] && count <= 15);
JSON_ASSERT(digits >= powers_of_ten()[static_cast<std::size_t>(count - 1)] && count <= 15);
const int scale = 16 - count;
return write_shortest(first, zmij::shortest_decimal{digits * powers_of_ten_16()[static_cast<std::size_t>(scale)], exp - scale - 1, 0, false});
return write_shortest(first, zmij::shortest_decimal{digits * powers_of_ten()[static_cast<std::size_t>(scale)], exp - scale - 1, 0, false});
}
/// as write_short_decimal(), counting the digits (not 0, less than 10^15)
@@ -28420,7 +28438,7 @@ inline char* write_short_decimal(char* first, std::uint64_t digits, int exp) noe
JSON_ASSERT(digits != 0 && digits < 1000000000000000u);
// floor(log10(2^bits)) + 1 digits, or one less
const int log2_bound = ((64 - count_leading_zeros(digits)) * 1233) >> 12;
const int count = log2_bound + (digits >= powers_of_ten_16()[static_cast<std::size_t>(log2_bound)] ? 1 : 0);
const int count = log2_bound + (digits >= powers_of_ten()[static_cast<std::size_t>(log2_bound)] ? 1 : 0);
return write_short_decimal(first, digits, count, exp);
}