History of Berkeley SoftFloat, to Release 3e

John R. Hauser
2018 January 20

Release 3e (2018 January)

• Changed the default numeric code for optional rounding mode odd (round to odd, also known as jamming) from 5 to 6.
• Modified the behavior of rounding mode odd when rounding to an integer value (either conversion to an integer format or a ‘roundToInt’ function). Previously, for those cases only, rounding mode odd acted the same as rounding to minimum magnitude. Now all operations are rounded consistently.
• Fixed some errors in the specialization code modeling Intel x86 floating-point, specifically the integers returned on invalid operations and the propagation of NaN payloads in a few rare cases.
• Added specialization code modeling ARM floating-point, conforming to VFPv2 or later.
• Added an example target for ARM processors.
• Fixed a minor bug whereby function f16_to_ui64 might return a different integer than expected in the case that the floating-point operand is negative.
• Added example target-specific optimization for GCC, employing GCC instrinsics and support for 128-bit integer arithmetic.
• Made other minor improvements.

Release 3d (2017 August)

• Fixed bugs in the square root functions for 64-bitdouble-precision, 80-bit double-extended-precision, and128-bit quadruple-precision. For 64-bit double-precision (f64_sqrt), the result could sometimes be off by 1 unit in the last place (1 ulp) from what it should be. For the larger formats, the square root could be wrong in a large portion of the less-significant bits. (A bug in f128_sqrt was first reported by Alexei Sibidanov.)

Release 3c (2017 February)

• Added optional rounding mode odd (round to odd, also known as jamming).
• Corrected the documentation concerning non-canonical representations in80-bit double-extended-precision.

Release 3b (2016 July)

• Implemented the common 16-bit “half-precision” floating-point format (float16_t).
• Made the integer values returned on invalid conversions to integer formats be determined by the port-specific specialization instead of being the same for all ports.
• Added preprocessor macro THREAD_LOCAL to allow the floating-point state (modes and exception flags) to be made per-thread.
• Modified the provided Makefiles to allow some options to be overridden from the make command.
• Made other minor improvements.

Release 3a (2015 October)

• Replaced the license text supplied by the University of California, Berkeley.

Release 3 (2015 February)

• Complete rewrite, funded by the University of California, Berkeley, and consequently having a different use license than earlier releases. Major changes included renaming most types and functions, upgrading some algorithms, restructuring the source files, and making SoftFloat into a true library.
• Added functions to convert between floating-point and unsigned integers, both32-bit and 64-bit (uint32_t and uint64_t).
• Added functions for fused multiply-add, for all supported floating-point formats except 80-bit double-extended-precision.
• Added support for a fifth rounding mode, near_maxMag (round to nearest, with ties to maximum magnitude, away from zero).
• Dropped the timesoftfloat program (now part of the Berkeley TestFloat package).

Release 2c (2015 January)

• Fixed mistakes affecting some 64-bit processors.
• Further improved the documentation and the wording for the legal restrictions on using SoftFloat releases through 2c (not applicable toRelease 3 or later).

Release 2b (2002 May)

• Made minor updates to the documentation, including improved wording for the legal restrictions on using SoftFloat.

Release 2a (1998 December)

• Added functions to convert between 64-bit integers (int64) and all supported floating-point formats.
• Fixed a bug in all 64-bit-version square root functions except float32_sqrt that caused the result sometimes to be off by1 unit in the last place (1 ulp) from what it should be. (Bug discovered by Paul Donahue.)
• Improved the Makefiles.

Release 2 (1997 June)

• Created the 64-bit (bits64) version, adding the floatx80 and float128 formats.
• Changed the source directory structure, splitting the sources into a bits32 and a bits64 version. Renamed environment.h to milieu.h to avoid confusion with environment variables.
• Fixed a small error that caused float64_round_to_int often to round the wrong way in nearest/even mode when the operand was between 220 and 221 and halfway between two integers.

Release 1a (1996 July)

• Corrected a mistake that caused borderline underflow cases not to raise the underflow flag when they should have. (Problem reported by Doug Priest.)
• Added the float_detect_tininess variable to control whether tininess is detected before or after rounding.

Release 1 (1996 July)

• Original release, based on work done for the International Computer Science Institute (ICSI) in Berkeley, California.