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#include "Half.h"
namespace nCine
{
inline namespace Primitives
{
union FloatBits {
std::uint32_t u;
float f;
};
// half_to_float_fast4() from https://gist.github.com/rygorous/2144712
float Half::UnpackHalf(const std::uint16_t value)
{
constexpr const FloatBits Magic { 113 << 23 };
// Exponent mask after shift
constexpr const std::uint32_t ShiftedExp = 0x7c00 << 13;
const std::uint16_t h { value };
FloatBits o;
o.u = (h & 0x7fff) << 13; // Exponent/mantissa bits
const std::uint32_t exp = ShiftedExp & o.u; // Just the exponent
o.u += (127 - 15) << 23; // Exponent adjust
// Handle exponent special cases
if (exp == ShiftedExp) { // Inf/NaN?
o.u += (128 - 16) << 23; // Extra exp adjust
} else if (exp == 0) { // Zero/Denormal
o.u += 1 << 23; // Extra exp adjust
o.f -= Magic.f; // Renormalize
}
o.u |= (h & 0x8000) << 16; // Sign bit
return o.f;
}
// float_to_half_fast3() from https://gist.github.com/rygorous/2156668
std::uint16_t Half::PackHalf(const float value)
{
constexpr const FloatBits FloatInfinity { 255 << 23 };
constexpr const FloatBits HalfInfinity { 31 << 23 };
constexpr const FloatBits Magic { 15 << 23 };
constexpr const std::uint32_t SignMask = 0x80000000u;
constexpr const std::uint32_t RoundMask = ~0xfffu;
FloatBits f;
f.f = value;
std::uint16_t h;
const std::uint32_t sign = f.u & SignMask;
f.u ^= sign;
// Note: all the integer compares in this function can be safely compiled
// into signed compares since all operands are below 0x80000000. Important
// if you want fast straight SSE2 code (since there's no unsigned PCMPGTD).
// Inf or NaN (all exponent bits set): NaN->qNaN and Inf->Inf
if (f.u >= FloatInfinity.u) {
h = (f.u > FloatInfinity.u) ? 0x7e00 : 0x7c00;
} else { // (De)normalized number or zero
f.u &= RoundMask;
f.f *= Magic.f;
f.u -= RoundMask;
// Clamp to signed infinity if overflowed
if (f.u > HalfInfinity.u) f.u = HalfInfinity.u;
// Take the bits!
h = f.u >> 13;
}
h |= sign >> 16;
return h;
}
}
}
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