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

digits_dec()

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 441 of file charconv.hpp.

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

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

digits_hex()

template<class T >

unsigned c4::digits_hex ( T  v )

inlinenoexcept

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

Definition at line 524 of file charconv.hpp.

{
    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;
}

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

digits_bin()

template<class T >

unsigned c4::digits_bin ( T  v )

inlinenoexcept

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

Definition at line 533 of file charconv.hpp.

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

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

digits_oct()

template<class T >

unsigned c4::digits_oct ( T  v_ )

inlinenoexcept

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

Definition at line 542 of file charconv.hpp.

{
    // 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
    unsigned __n = 1;
    const unsigned __b2 = 64u;
    const unsigned __b3 = __b2 * 8u;
    const unsigned long __b4 = __b3 * 8u;
    while(true)
    {
        if(v < 8u)
            return __n;
        if(v < __b2)
            return __n + 1;
        if(v < __b3)
            return __n + 2;
        if(v < __b4)
            return __n + 3;
        v /= (U) __b4;
        __n += 4;
    }
}

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