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#pragma once
/*
* This code snippet posted by user Phernost on
* https://stackoverflow.com/questions/1659440/32-bit-to-16-bit-floating-point-conversion
*
* compress and decompress methods are made "inline" for performance
*/
class Float16Compressor
{
union Bits
{
float f;
int32_t si;
uint32_t ui;
};
static int const shift = 13;
static int const shiftSign = 16;
static int32_t const infN = 0x7F800000; // flt32 infinity
static int32_t const maxN = 0x477FE000; // max flt16 normal as a flt32
static int32_t const minN = 0x38800000; // min flt16 normal as a flt32
static int32_t const signN = 0x80000000; // flt32 sign bit
static int32_t const infC = infN >> shift;
static int32_t const nanN = (infC + 1) << shift; // minimum flt16 nan as a flt32
static int32_t const maxC = maxN >> shift;
static int32_t const minC = minN >> shift;
static int32_t const signC = signN >> shiftSign; // flt16 sign bit
static int32_t const mulN = 0x52000000; // (1 << 23) / minN
static int32_t const mulC = 0x33800000; // minN / (1 << (23 - shift))
static int32_t const subC = 0x003FF; // max flt32 subnormal down shifted
static int32_t const norC = 0x00400; // min flt32 normal down shifted
static int32_t const maxD = infC - maxC - 1;
static int32_t const minD = minC - subC - 1;
public:
inline static uint16_t compress(float value)
{
Bits v, s;
v.f = value;
uint32_t sign = v.si & signN;
v.si ^= sign;
sign >>= shiftSign; // logical shift
s.si = mulN;
s.si = s.f * v.f; // correct subnormals
v.si ^= (s.si ^ v.si) & -(minN > v.si);
v.si ^= (infN ^ v.si) & -((infN > v.si) & (v.si > maxN));
v.si ^= (nanN ^ v.si) & -((nanN > v.si) & (v.si > infN));
v.ui >>= shift; // logical shift
v.si ^= ((v.si - maxD) ^ v.si) & -(v.si > maxC);
v.si ^= ((v.si - minD) ^ v.si) & -(v.si > subC);
return v.ui | sign;
}
inline static float decompress(uint16_t value)
{
Bits v;
v.ui = value;
int32_t sign = v.si & signC;
v.si ^= sign;
sign <<= shiftSign;
v.si ^= ((v.si + minD) ^ v.si) & -(v.si > subC);
v.si ^= ((v.si + maxD) ^ v.si) & -(v.si > maxC);
Bits s;
s.si = mulC;
s.f *= v.si;
int32_t mask = -(norC > v.si);
v.si <<= shift;
v.si ^= (s.si ^ v.si) & mask;
v.si |= sign;
return v.f;
}
}; |