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- TODO LIST
- =========
- ::
- POW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - power
- RPW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse power
- POL{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - polar angle (arctan2)
- LOG{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base 10
- LGN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base e
- EXP{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - exponent
- SIN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - sine
- COS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - cosine
- TAN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - tangent
- ASN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arcsine
- ACS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arccosine
- ATN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arctangent
- These are not implemented. They are not currently issued by the compiler,
- and are handled by routines in libc. These are not implemented by the FPA11
- hardware, but are handled by the floating point support code. They should
- be implemented in future versions.
- There are a couple of ways to approach the implementation of these. One
- method would be to use accurate table methods for these routines. I have
- a couple of papers by S. Gal from IBM's research labs in Haifa, Israel that
- seem to promise extreme accuracy (in the order of 99.8%) and reasonable speed.
- These methods are used in GLIBC for some of the transcendental functions.
- Another approach, which I know little about is CORDIC. This stands for
- Coordinate Rotation Digital Computer, and is a method of computing
- transcendental functions using mostly shifts and adds and a few
- multiplications and divisions. The ARM excels at shifts and adds,
- so such a method could be promising, but requires more research to
- determine if it is feasible.
- Rounding Methods
- ----------------
- The IEEE standard defines 4 rounding modes. Round to nearest is the
- default, but rounding to + or - infinity or round to zero are also allowed.
- Many architectures allow the rounding mode to be specified by modifying bits
- in a control register. Not so with the ARM FPA11 architecture. To change
- the rounding mode one must specify it with each instruction.
- This has made porting some benchmarks difficult. It is possible to
- introduce such a capability into the emulator. The FPCR contains
- bits describing the rounding mode. The emulator could be altered to
- examine a flag, which if set forced it to ignore the rounding mode in
- the instruction, and use the mode specified in the bits in the FPCR.
- This would require a method of getting/setting the flag, and the bits
- in the FPCR. This requires a kernel call in ArmLinux, as WFC/RFC are
- supervisor only instructions. If anyone has any ideas or comments I
- would like to hear them.
- NOTE:
- pulled out from some docs on ARM floating point, specifically
- for the Acorn FPE, but not limited to it:
- The floating point control register (FPCR) may only be present in some
- implementations: it is there to control the hardware in an implementation-
- specific manner, for example to disable the floating point system. The user
- mode of the ARM is not permitted to use this register (since the right is
- reserved to alter it between implementations) and the WFC and RFC
- instructions will trap if tried in user mode.
- Hence, the answer is yes, you could do this, but then you will run a high
- risk of becoming isolated if and when hardware FP emulation comes out
- -- Russell.
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