IBM hexadecimal floating-point

Floating-point formats
IEEE 754
Other
Alternatives
Tapered floating point

Hexadecimal floating point (now called HFP by IBM) is a format for encoding floating-point numbers first introduced on the IBM System/360 computers, and supported on subsequent machines based on that architecture,[1][2][3] as well as machines which were intended to be application-compatible with System/360.[4][5]

In comparison to IEEE 754 floating point, the HFP format has a longer significand, and a shorter exponent. All HFP formats have 7 bits of exponent with a bias of 64. The normalized range of representable numbers is from 16−65 to 1663 (approx. 5.39761 × 10−79 to 7.237005 × 1075).

The number is represented as the following formula: (−1)sign × 0.significand × 16exponent−64.

  1. ^ IBM System/360 Principles of Operation, IBM Publication A22-6821-6, Seventh Edition (January 13, 1967), pp.41-50
  2. ^ IBM System/370 Principles of Operation, IBM Publication GA22-7000-4, Fifth Edition (September 1, 1975), pp.157-170
  3. ^ z/Architecture Principles of Operation, IBM Publication SA22-7832-01, Second Edition (October, 2001), chapter 9 ff.
  4. ^ Xerox Data Systems (Oct 1973). Xerox SIGMA 7 Computer Reference Manyal. p. 48. Retrieved Nov 13, 2020.
  5. ^ RCA (Mar 1966). Spectra 70 processors: 35 45 55 (PDF). p. 184. Retrieved Nov 13, 2020.