Luna/libluna/src/Units.cpp

#include <luna/Alloc.h>
#include <luna/CType.h>
#include <luna/Result.h>
#include <luna/ScopeGuard.h>
#include <luna/Units.h>

Result<String> to_dynamic_unit(usize value, usize round_after, bool separate, Unit unit, bool display_unit)
{
    const usize multiplier = (usize)unit;
    if (value < multiplier) { return String::format("%zu%s"_sv, value, display_unit ? " bytes" : ""); }

    bool si = unit == Unit::SI;

    const char* unit_prefixes = "KMGTPE";
    if (si) unit_prefixes = "kMGTPE";
    while (value > (multiplier * multiplier))
    {
        value /= multiplier;
        unit_prefixes++;
    }

    const usize divider = (si ? 100 : 103);

    usize fixed = value / multiplier;
    usize rest = (value % multiplier) / divider;
    bool round = fixed >= round_after;

    if (round)
    {
        if (value % multiplier) fixed++;
        return String::format("%zu%s%c%s"_sv, fixed, separate ? " " : "", *unit_prefixes,
                              display_unit ? (si ? "B" : "iB") : "");
    }

    if ((value % multiplier) % divider) rest++;
    if (rest > 9)
    {
        rest = 0;
        fixed++;
    }

    return String::format("%zu.%zu%s%c%s"_sv, fixed, rest, separate ? " " : "", *unit_prefixes,
                          display_unit ? (si ? "B" : "iB") : "");
}