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Half PrecisionIn computing, half precision is a computer numbering format that occupies only half of one storage locations in computer memory at address. A half-precision number may be defined to be an integer, fixed point, or floating point. For integers, they are typically called short. Half-precision floating point is a relatively new format that uses 2 bytes and which is not covered by the IEEE 754 standard for encoding floating point numbers. This format is used in several computer graphics environments including OpenEXR, OpenGL, and D3DX. The advantage over 8-bit or 16-bit integer is that the increased dynamic range allows for details to be preserved in highlights and shadows. The advantage over 32-bit single precision formats (such as TIFF) is that it requires half the storage and bandwidth. http://www.openexr.org/details.html Half precision memory format Sign bit: 1 Exponent width: 5 Significand precision: 11 The format is written with an implicit integer bit with value 1 unless the written exponent is all zeros. Thus only 10 bits of the fraction appear in the memory format. syyy yyxx xxxx xxxx (10 xs) Exponent encodings Emin (0x01) = −14 Emax (0x1e) = 15 Exponent bias (0x0f) = 15 The true exponent = written exponent − exponent bias 0x00 and 0x1f are reserved exponents 0x00 is used to represent zero and denormals 0x1f is used to represent infinity and NaNs All bit patterns are valid encodings. Half-precision examples in hexadecimal 3c00 = 1 c000 = -2 7dff = 65504 (Max Half precision) 3555 ~ 0.3325... ~ 1/3 (1/3 rounds down like double precision, because of the odd number of bits in the significand.) 0000 = 0 8000 = -0 7c00 = Infinity fc00 = -Infinity Usage note Pedantic note: When using half-precision as an adjective, as in half-precision number, hyphenate it. When using it as a noun ("Single precision differs from half precision."), do not hyphenate it. See also External links
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