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SoftIEEE provides both a high-precision mathematical floating point
library for 80 bit (extended precision) floating point operations, and
a software based FPU emulator for FPU-less Motorola processors, from
68000 to 68LC060. That is, even a 68000 can be equipped with a
"virtual FPU" (albeit a very slow one).
Purpose and goal of SoftIEEE:
- Provide high-precision mathematics with 80 bit precision, including
elementary and transcental functions. The overall precision of this
library exceeds the precision of the 68881/882 FPUs.
- Provide a software emulator for 68881/882 and other Motorola FPUs
such that FPU-based programs can be used natively on FPU-less
systems. Programs not depending on an FPU will execute in normal
speed without any penalty, though FPU emulation is naturally slower
than on a system equipped with a FPU. FPU-less does not only include
the 68LC040 and 68LC060 processors, also 68030 and smaller
processors can be equipped with a virtual FPU.
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Installation:
- Copy the softieee.library to LIBS:
This library implements the numerical algorithms of the FPU,
such as addition, multiplication... and also transcental
functions such as sin() and cos().
The library can also be used without the FPU emulation for
high-precision mathematics. It is approximately equivalent
to the mathieeedoubbas/doubtrans system libraries, but
is able to compute in single, double and extended precision,
through a single unified code.
- Copy SoftIEEE to C:
This binary is the actual FPU implementation that uses the
softieee.library for the numerical algorithms.
- Run SoftIEEE in the startup-sequence, somewhere below
SetPatch. There are typically no arguments required.
- Due to emulation, executables may require approximately
400 bytes more stack. Thus, it may be wise to increase
the default stack size by this amount.
Caveats:
- Note that programs that take over the system will most
likely not be able to use the emulated FPU. This is
because they typically may damage the Line-F exception
vector or the SoftIEEE code.
- Some games or game loaders may simply overwrite or
replace the LineF exception handler and hence may not
profit from SoftIEEE. Similarly, some system monitors
or information systems may, in an attempt to detect a
FPU, overwrite the LineF hander. Detecting a FPU should
go through the ExecBase "AttnFlags" field, and not
through a custom detection logic.
- Note further that SoftIEEE critically depends on the
Line-F exception processing and the CPU exception
stack frame. Emulated CPUs may not implement these
details correctly. SoftIEEE is designed for real
hardware and is not suitable for emulation.
- Members of the 68060 processor family need some special
preparation of the operating system not all 68060.libraries
may patch in if no FPU is found. This is because some of these
preparations are FPU related and may be omitted if no FPU is
(initially) found. The 68060.library that is part of the MMULib
distribution performs these preparations regardless of the
availability of the FPU and thus should be preferred for
running SoftIEEE. Note that this library supports all
members of the 68060 processor family, regardless its name.
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SoftIEEE is a quite complex program, and as every piece of software,
it may contain bugs or inaccuracies. While I'm happy to fix such
problems, I need your help to identify them. Thus, in case you find
that a particular program does not operate correctly, please provide
the following:
*) Detailed instructions on how to reproduce the problem, including
the software causing the problem. That is, it is not sufficient to
say "Software XYZ does not work", but please provide the steps needed
to trigger the problem, i.e. "...I see a problem if I open the
attached file with software XYZ and then click on button ABC".
*) Also, please install MuForce, SegTracker and Sashimi (all in the
Aminet), then run SegTracker first, followed by Sashimi, then MuForce
with the DISPC command line option. As soon as you see a crash,
MuForce should trigger an output of Sashimi. Please provide me this
output. This will help tremendously to narrow down the issue.
Thank you,
Thomas
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SoftIEEE command line arguments:
SoftIEEE FPUID/K/N,HIDDEN/S,STAYINSUPER/S
- FPUID sets the coprocessor ID for the emulated FPU. By default,
the FPUID is 1, which is the coprocessor ID Motorola recommends
for floating point processors, and the ID used by the internal
FPU of the 68040 and 68060 processors.
Note that most (if not all) programs only recognize the (emulated)
FPU under ID=1.
FPUIDs 0, 2, and 3, even though possible, should NOT be used as they
encode instructions for the MMU, cache control and other extended
instructions.
Generally, IDs different from 1 are only useful for debugging.
- HIDDEN hides the FPU from the operating system. If this option is
used, then even though the emulated FPU is operational, it is not
announced and programs that offer algorithms optimized for systems
with and without FPU will select the CPU-based algorithm, thus may
operate faster than through the emulation. System monitors or system
debuggers will still not see the emulated FPU then.
- STAYINSUPER instructs SoftIEEE not to perform lengthy FPU emulation
functions in user mode, as it would typically do. Setting this
option may help to improve performance somewhat as the CPU exception
stack frame does not need to be copied to the user stack. However,
this may have a negative input on the responsiveness of the machine
as exec cannot schedule tasks within the supervisor mode.
SoftIEEE can also be run from the workbench. It takes the following
tool types:
HIDDEN This tool type does not take any arguments. If set,
the FPU is not announced to the system. Works
identically to the command line argument of the same
name.
STAYINSUPER This tool type neither takes any arguments. If set,
emulation does not switch back to user mode for
lengthy FPU instructions. Works identical to the
command line argument of the same name.
FPUID=n Sets the coprocessor ID for the FPU to be emulated. By
default, this is 1, which is also the coprocessor ID
Motorola recommends for the FPU. Works identically to
the command line argument of the same name.
WINDOW=<path> Sets the path under which SoftIEEE outputs errors, if
any. By default, a CON: window is opened.
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SoftIEEE consists of two components. The SoftIEEE command line tool
which contains the FPU emulation and the interpreter for FPU commands.
More on the SoftIEEE binary can be found in the "interna.doc" file
which explains some details of the emulation process.
The second component is the softieee.library which implements the
numerical algorithms used by the FPU emulator of the command line. The
softieee.library can be used independently of the FPU emulation if
high-precision (80 bit) mathematical algorithms are required.
The documentation of the softieee.library can be found in autodoc
format in "softieee.doc".
This library implements 80 bit precision mathematics, with some
internal computations even carried out with 96 bit precision. Similar
to the 68881/882 FPU, the rounding precision and rounding mode are
selectable. The precision of these algorithms exceed those of the
system libraries and for some cases even that of the hardware.
The precision of the elementary functions is 0.5ulp (1/2 least
significant digit) in the round-to-nearest mode, or 1ulp in all other
rounding modes. This is identical to what the 68881/882 deliver.
The precision of most transcendental functions is typically 1ulp or
2ulp depending on the function, which is much better than the hardware
implementation in the 68881/882 coprocessors which only offers double
precision for such functions.
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Release 40.0
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- First beta release for testing.
Release 40.1
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- The fmovecr instruction had the table entries B and C
exchanged. Thanks Peter for reporting.
- The task reschedule algorithm for the 68LC060 processor
restored its stack frame twice, and hence crashed the
machine. It was fine for all other processors.
- The frestore emulation had a serious defect and read
the ea from the wrong address, potentially trashing
registers.
- The single precision rounding algorithm exclusively used
for fsglmul and fsgldiv did not install the sign of
the result correctly.
- Moving a floating point register to a data register did
not work correctly.
- The frestore and fsave instruction on the 68060 did not
use the right function codes when reading indirectly
from the PC.
- fmovem of FPU registers or control registers failed in
case the register list was empty (essentially, a NOP).
- fmovem to or from control registers with an empty
register list did not properly emulate the hardware
implementation which would, in this case, transmit
the FPIAR.
- ExtToPacked and PackedToExt affected the condition
codes, even though it should not.
- Emulation of fmove into the FPU should have set the
condition code, but it did not.
- The emulation of the 68040 and 68060 instructions
fsmove and fdmove were missing.
- The conversions between packed and extended precision
touched the FPSR condition codes, though they should
not as flags are handled outside, and the side effect
would be inconsistent with the fmove to memory emulation.
- fmove from memory to a register did not set condition
codes correctly as it used the wrong address register
for testing. Again, thanks goes to Peter for helping
me to narrow the issue down.
- ftst used incorrectly the destination register for
testing, though this register is not even used by
the instruction.
Release 40.2
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- Replaced CORDIC by Specker's algorithm for the
computation of log, exp, log2 and twotox. This
algorithm is somewhat faster for these functions.
cosh, sinh and atanh remain CORDIC based.
- Forgot to process the fdneg and fsneg instructions
of the 68040.
- Signalling NaNs where not always reported
correctly.
- Conversions out of the simulated FPU incorrectly
set the condition codes.
- Testing for INFs and NANs did not ignore the MSB
of the mantissa as it should.
- Conversion of INFs, NANs or out-of-range numbers
to integers did not generate the correct results.
- Emulation of the 68040/68060 instructions fsneg,
fdneg, fssqrt and fdsqrt were missing.
- Apparently, some masks of the 68LC060 contain an
erratum where the processor fails to place the
effective address of fmovem <ea>,fpx on the
exception stack. SoftIEEE now computes the effective
address of fmovem (both FPU and control registers)
and frestore itself.
- The exponential threshold on which an extended
precision overflows to INF when converting to double
or single precision was off by one.
Release 40.3
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- bumped the last release to 40.3, no changes.
- first Aminet release. Previous releases were
beta software.
Release 40.4
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- The 68060 erratum present in some FPU instructions
seem to affect additional instructions, at least fsave
neither reports the proper effective address in the
stack frame. To be on the safe side, SoftIEEE now also
enables the workaround for fmovem (all types) and fsave.
It was already active for frestore. Unfortunately, even
the latest mask sets of the CPU are affected.
- frestore emulation on the 68060 checked for the wrong
stack frame and thus caused format errors when issued on
a busy (emulated) FPU. The problem did not manifest in
the exec context switch because it goes directly through
the softieee.library and not through the emulation core.
- fsave after an FPU exception did not report any exceptional
operand correctly as this was taken from the activation
record which was, however, not necessarily the same record
that was involved when creating the exception. Instead,
the code now places error operands in the library base
when creating an FPU exception and takes them from there
upon an fsave.
- The low-level debugger COP in its version 1.105 became now
compatible with SoftIEEE. To inspect the state of the
"virtual FPU", run it with the command line argument
NOFPUEMU to avoid COP from capturing FPU emulator traps.
Release 40.5
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- The extension word(s) of the ftrapcc instructions were not
skipped correctly as they should have.
- SoftIEEE creates now the softieee.resource to make future
versions of MuRedox aware of its presence.
Release 40.6
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- SoftIEEE caused a line-F trap in case it encountered an
fmovem instruction with an irregular register move order.
While the Motorola manual recommends only certain orders
for certain addressing modes, both register move orders
work actually in all situations. This has been fixed.
Release 40.6.1
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- Apparently, I forgot to bump the revision for the last
release. Other than that, the binaries did not change.
- Some minor improvements on the documentation has been
made such as clarifying where condition codes and FPU
configuration are kept and how to retrieve them.
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The THOR-Software Licence (v3, January 2nd 2021)
This License applies to the computer programs known as
"softieee.library", "SoftIEEE" and its includes and autodocs. The
"Program", below, refers to such program. The "Archive" refers to the
the original and unmodified package of distribution, as prepared by
the author of the Program.
The Program and the data in the archive are freely distributable under
the restrictions stated below, but are also Copyright (c) Thomas
Richter.
Distribution of the Program, the Archive and the data in the Archive
by a commercial organization without written permission from the
author to any third party is prohibited if any payment is made in
connection with such distribution, whether directly (as in payment for
a copy of the Program) or indirectly (as in payment for some service
related to the Program, or payment for some product or service that
includes a copy of the Program "without charge"; these are only
examples, and not an exhaustive enumeration of prohibited activities).
However, the following methods of distribution involving payment shall
not in and of themselves be a violation of this restriction:
(i) Distributing the Program on a physical data carrier (e.g. CD-ROM,
DVD, USB-Stick, Disk...) provided that:
a) the Archive is reproduced entirely and verbatim on such data carrier,
including especially this licence agreement;
b) the data carrier is made available to the public for a nominal
fee only, i.e. for a fee that covers the costs of the data carrier,
and shipment of the data carrier;
c) a data carrier with the Program installed is made available to the
author for free except for shipment costs, and
d) provided further that all information on said data carrier is
redistributable for non-commercial purposes without charge.
Redistribution of a modified version of the Archive, the Program or
the contents of the Archive is prohibited in any way, by any
organization, regardless whether commercial or
non-commercial. Everything must be kept together, in original and
unmodified form.
Limitations.
THE PROGRAM IS PROVIDED TO YOU "AS IS", WITHOUT WARRANTY. THERE IS NO
WARRANTY FOR THE PROGRAM, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY
RIGHTS. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE
PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME
THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IF YOU DO NOT ACCEPT THIS LICENCE, YOU MUST DELETE THE PROGRAM, THE
ARCHIVE AND ALL DATA OF THIS ARCHIVE FROM YOUR STORAGE SYSTEM. YOU
ACCEPT THIS LICENCE BY USING OR REDISTRIBUTING THE PROGRAM.
Thomas Richter, January 2021
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So long,
Thomas (January 2023)
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