mirror of
https://github.com/simdjson/simdjson
synced 2026-06-08 17:27:07 +00:00
John Keiser
60 lines
1.8 KiB
C++
60 lines
1.8 KiB
C++
#ifndef SIMDJSON_INTERNAL_NUMBERPARSING_TABLES_H
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#define SIMDJSON_INTERNAL_NUMBERPARSING_TABLES_H
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#include "simdjson/base.h"
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namespace simdjson {
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namespace internal {
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/**
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* The smallest non-zero float (binary64) is 2^-1074.
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* We take as input numbers of the form w x 10^q where w < 2^64.
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* We have that w * 10^-343 < 2^(64-344) 5^-343 < 2^-1076.
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* However, we have that
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* (2^64-1) * 10^-342 = (2^64-1) * 2^-342 * 5^-342 > 2^-1074.
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* Thus it is possible for a number of the form w * 10^-342 where
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* w is a 64-bit value to be a non-zero floating-point number.
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*********
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* Any number of form w * 10^309 where w>= 1 is going to be
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* infinite in binary64 so we never need to worry about powers
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* of 5 greater than 308.
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*/
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constexpr int smallest_power = -342;
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constexpr int largest_power = 308;
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/**
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* Represents a 128-bit value.
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* low: least significant 64 bits.
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* high: most significant 64 bits.
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*/
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struct value128 {
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uint64_t low;
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uint64_t high;
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};
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// Precomputed powers of ten from 10^0 to 10^22. These
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// can be represented exactly using the double type.
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extern SIMDJSON_DLLIMPORTEXPORT const double power_of_ten[];
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/**
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* When mapping numbers from decimal to binary,
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* we go from w * 10^q to m * 2^p but we have
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* 10^q = 5^q * 2^q, so effectively
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* we are trying to match
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* w * 2^q * 5^q to m * 2^p. Thus the powers of two
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* are not a concern since they can be represented
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* exactly using the binary notation, only the powers of five
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* affect the binary significand.
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*/
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// The truncated powers of five from 5^-342 all the way to 5^308
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// The mantissa is truncated to 128 bits, and
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// never rounded up. Uses about 10KB.
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extern SIMDJSON_DLLIMPORTEXPORT const uint64_t power_of_five_128[];
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} // namespace internal
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} // namespace simdjson
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#endif // SIMDJSON_INTERNAL_NUMBERPARSING_TABLES_H
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