simdjson_fast_float::powers_template< unused > Struct Template Reference

When mapping numbers from decimal to binary, we go from w * 10^q to m * 2^p but we have 10^q = 5^q * 2^q, so effectively we are trying to match w * 2^q * 5^q to m * 2^p. More...

#include <fast_float.h>

Static Public Attributes
static constexpr int	smallest_power_of_five
static constexpr int	largest_power_of_five
static constexpr int	number_of_entries
static constexpr uint64_t	power_of_five_128 [number_of_entries]

Detailed Description

template<class unused = void>
struct simdjson_fast_float::powers_template< unused >

When mapping numbers from decimal to binary, we go from w * 10^q to m * 2^p but we have 10^q = 5^q * 2^q, so effectively we are trying to match w * 2^q * 5^q to m * 2^p.

Thus the powers of two are not a concern since they can be represented exactly using the binary notation, only the powers of five affect the binary significand. The smallest non-zero float (binary64) is 2^-1074. We take as input numbers of the form w x 10^q where w < 2^64. We have that w * 10^-343 < 2^(64-344) 5^-343 < 2^-1076. However, we have that (2^64-1) * 10^-342 = (2^64-1) * 2^-342 * 5^-342 > 2^-1074. Thus it is possible for a number of the form w * 10^-342 where w is a 64-bit value to be a non-zero floating-point number.

Any number of form w * 10^309 where w>= 1 is going to be infinite in binary64 so we never need to worry about powers of 5 greater than 308.

Definition at line 2597 of file fast_float.h.

Member Data Documentation

largest_power_of_five

template<class unused = void>

constexpr int simdjson_fast_float::powers_template< unused >::largest_power_of_five

staticconstexpr

Initial value:

=
      binary_format<double>::largest_power_of_ten()

Definition at line 2601 of file fast_float.h.

number_of_entries

template<class unused = void>

constexpr int simdjson_fast_float::powers_template< unused >::number_of_entries

staticconstexpr

Initial value:

=
      2 * (largest_power_of_five - smallest_power_of_five + 1)

Definition at line 2603 of file fast_float.h.

power_of_five_128

template<class unused >

constexpr uint64_t simdjson_fast_float::powers_template< unused >::power_of_five_128

staticconstexpr

Definition at line 2606 of file fast_float.h.

smallest_power_of_five

template<class unused = void>

constexpr int simdjson_fast_float::powers_template< unused >::smallest_power_of_five

staticconstexpr

Initial value:

=
      binary_format<double>::smallest_power_of_ten()

Definition at line 2599 of file fast_float.h.

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The documentation for this struct was generated from the following file:

• include/simdjson/internal/fast_float.h