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diff --git a/Documentation/arch/arm/nwfpe/todo.rst b/Documentation/arch/arm/nwfpe/todo.rst new file mode 100644 index 0000000000..393f11b145 --- /dev/null +++ b/Documentation/arch/arm/nwfpe/todo.rst @@ -0,0 +1,72 @@ +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. |