chromium/third_party/fast_float/src/include/fast_float/fast_table.h

#ifndef FASTFLOAT_FAST_TABLE_H
#define FASTFLOAT_FAST_TABLE_H

#include <cstdint>

namespace fast_float {

/**
 * 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.
 */
template <class unused = void> struct powers_template { … };

template <class unused>
constexpr uint64_t
    powers_template<unused>::power_of_five_128[number_of_entries];

powers;

} // namespace fast_float

#endif