Get number of digits

Functions
template<class T >
auto	c4::digits_dec (T v) noexcept-> typename std::enable_if< sizeof(T)==1u, unsigned >::type
	decimal digits for 8 bit integers More...
template<class T >
unsigned	c4::digits_hex (T v) noexcept
	return the number of digits required to encode an hexadecimal number. More...
template<class T >
unsigned	c4::digits_bin (T v) noexcept
	return the number of digits required to encode a binary number. More...
template<class T >
unsigned	c4::digits_oct (T v_) noexcept
	return the number of digits required to encode an octal number. More...

Detailed Description

Note

At first sight this code may look heavily branchy and therefore inefficient. However, measurements revealed this to be the fastest among the alternatives.

See also

https://github.com/biojppm/c4core/pull/77

Function Documentation

template<class T >

auto c4::digits_dec ( T  v ) -> typename std::enable_if<sizeof(T) == 1u, unsigned>::type

inlinenoexcept

decimal digits for 8 bit integers

decimal digits for 64 bit integers

decimal digits for 32 bit integers

decimal digits for 16 bit integers

Definition at line 432 of file charconv.hpp.

Referenced by c4::itoa(), c4::utoa(), c4::write_dec(), and c4::write_dec_unchecked().

{
    C4_STATIC_ASSERT(std::is_integral<T>::value);
    C4_ASSERT(v >= 0);
    return ((v >= 100) ? 3u : ((v >= 10) ? 2u : 1u));
}

template<class T >

unsigned c4::digits_hex ( T  v )

inlinenoexcept

return the number of digits required to encode an hexadecimal number.

Definition at line 529 of file charconv.hpp.

Referenced by c4::itoa(), c4::utoa(), c4::write_hex(), and c4::write_hex_unchecked().

{
    C4_STATIC_ASSERT(std::is_integral<T>::value);
    C4_ASSERT(v >= 0);
    return v ? 1u + (msb((typename std::make_unsigned<T>::type)v) >> 2u) : 1u;
}

template<class T >

unsigned c4::digits_bin ( T  v )

inlinenoexcept

return the number of digits required to encode a binary number.

Definition at line 538 of file charconv.hpp.

Referenced by c4::itoa(), c4::utoa(), c4::write_bin(), and c4::write_bin_unchecked().

{
    C4_STATIC_ASSERT(std::is_integral<T>::value);
    C4_ASSERT(v >= 0);
    return v ? 1u + msb((typename std::make_unsigned<T>::type)v) : 1u;
}

template<class T >

unsigned c4::digits_oct ( T  v_ )

inlinenoexcept

return the number of digits required to encode an octal number.

Definition at line 547 of file charconv.hpp.

Referenced by c4::itoa(), c4::utoa(), c4::write_oct(), and c4::write_oct_unchecked().

{
    // TODO: is there a better way?
    C4_STATIC_ASSERT(std::is_integral<T>::value);
    C4_ASSERT(v_ >= 0);
    using U = typename std::conditional<sizeof(T) <= sizeof(unsigned),
                                        unsigned,
                                        typename std::make_unsigned<T>::type>::type;
    U v = (U) v_;  // safe because we require v_ >= 0 // NOLINT
    uint32_t n_ = 1;
    enum : U {
        b2_ = 64u,
        b3_ = 64u * 8u,
        b4_ = 64u * 8u * 8u,
    };
    while(true)
    {
        if(v < 8u)
            return n_;
        else if(v < b2_)
            return n_ + 1;
        else if(v < b3_)
            return n_ + 2;
        else if(v < b4_)
            return n_ + 3;
        v /= (U) b4_;
        n_ += 4;
    }
}