TIFF and LibTiff Mail List Archive

# 2013.02.15 14:09 "Re: [Tiff] TIFF support for 16 bit floats", by Charles Auer

//////////////////////////////////////////////////////
//
// CONVERT HALF FLOAT (16 BIT FLOAT) TO FLOAT
//
////////////////////////////////////////////////////// // -15 stored using a single precision bias of 127
const unsigned int HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP = 0x38000000; // max exponent value in single precision that will be converted
// to Inf or Nan when stored as a half-float
const unsigned int HALF_FLOAT_MAX_BIASED_EXP_AS_SINGLE_FP_EXP = 0x47800000; // 255 is the max exponent biased value

const unsigned int  FLOAT_MAX_BIASED_EXP = (0xFF << 23); const unsigned int  HALF_FLOAT_MAX_BIASED_EXP = (0x1F << 10); typedef unsigned short    hfloat;

float convertHFloatToFloat(hfloat hf)
{

unsigned int    sign = (unsigned int)(hf >> 15);
unsigned int    mantissa = (unsigned int)(hf & ((1 << 10) - 1));
unsigned int    exp = (unsigned int)(hf & HALF_FLOAT_MAX_BIASED_EXP);
unsigned int    f;  if (exp == HALF_FLOAT_MAX_BIASED_EXP)

{
// we have a half-float NaN or Inf
// half-float NaNs will be converted to a single precision NaN
// half-float Infs will be converted to a single precision Inf
exp = FLOAT_MAX_BIASED_EXP;
if (mantissa)
mantissa = (1 << 23) - 1; // set all bits to indicate a NaN
}
else if (exp == 0x0)
{
// convert half-float zero/denorm to single precision value
if (mantissa)
{
mantissa <<= 1;
exp = HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
// check for leading 1 in denorm mantissa
while ((mantissa & (1 << 10)) == 0)
{
// for every leading 0, decrement single precision exponent by 1
// and shift half-float mantissa value to the left
mantissa <<= 1;
exp -= (1 << 23);
}
// clamp the mantissa to 10-bits
mantissa &= ((1 << 10) - 1);
// shift left to generate single-precision mantissa of 23-bits
mantissa <<= 13;
}
}
else
{
// shift left to generate single-precision mantissa of 23-bits
mantissa <<= 13;
// generate single precision biased exponent value
exp = (exp << 13) + HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
} f = (sign << 31) | exp | mantissa;
return *((float *)&f);
}