48-bit floating point

Norsk Data 48-bit floating point format:

The NORD-10 and the ND-100 could use two different hardware floating point formats, either the 48-bit format described on this page, or alternatively ordered with 32-bit floating point hardware.

The ND-500 and ND-5000 used only the 32-bit floating point format for single precision, and 64-bit floating point as double precision. The ND-100 (or -110, -120) front ends in those systems would normally have come with the 32-bit option in order to be compatible with their 500(0) companion. The 48-bit format described on this page is only used by the 16-bit ND computers.

Field	#Bits	Purpose
bit 47	1	Sign bit
bit 46-32	15	Exponent
bit 31-0	32	Mantissa

• The mantissa is normalized: 0.5 ≤ mantissa < 1
• The mantissa has no implicit bit, unlike the 32-bit and 64-bit formats
• The decimal point is thus to the left of the 32th bit (before exponent is applied)
• The exponent has a bias of 2¹⁴, or 16384 (subtract 16384 to get true exponent)

Special values

• All 48 bits zero: Zero.
• (Any special value (e.g. -0) reprecenting floating point underflow is not documented in the ND-100 reference manual)

Precision

• 32 bits or approximately 10 decimal digits

Range

• 2^-16384 - 0.5 ≤ X < 2¹⁶³⁸³ - 1 or X = 0

or

• approximately 10^-4920 < X < 10⁴⁹²⁰

Sources

• Norsk Data Document ND–06.014.02 ND-100 REFERENCE MANUAL