schubfachpowgen

schubfachpowgen is a command-line tool that generates the lookup table of powers of 10 used by the Schubfach algorithm.

Each power of 10 is stored on 126 bits, rounded up, as a high and a low 64-bit word.

The tool outputs a fully self-contained C++ header containing:

• MIN_EXPONENT, MAX_EXPONENT
• a Power { uint64_t hi; uint64_t lo; } structure
• a constexpr Power powers[] lookup table

Usage

Option	Description
-h	Show help message
-l <lower>	Set lower exponent (default: -292)
-u <upper>	Set upper exponent (default: 324)
-v	Show program version

Example

Generate powers for exponents −200 through +200 and write them to power.hpp:

 bash
schubfachpowgen -l -200 -u 200 > power.hpp

The generated header will contain definitions like:

 cpp
#ifndef __POWER_HPP__
#define __POWER_HPP__
 
#include <cstdint>
 
#define MIN_EXPONENT -200
#define MAX_EXPONENT 200
 
struct Power {
    uint64_t hi;
    uint64_t lo;
};
 
constexpr Power powers[] = {
    {0x1234567890abcdef, 0xfedcba0987654321},
    ...
    ...
    ...
};
 
#endif

License

MIT