From 76cb841cb886eef6b3bee341a2266c76578724ad Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:02:30 +0200 Subject: Adding upstream version 4.19.249. Signed-off-by: Daniel Baumann --- Documentation/arm/nwfpe/TODO | 67 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 Documentation/arm/nwfpe/TODO (limited to 'Documentation/arm/nwfpe/TODO') diff --git a/Documentation/arm/nwfpe/TODO b/Documentation/arm/nwfpe/TODO new file mode 100644 index 000000000..8027061b6 --- /dev/null +++ b/Documentation/arm/nwfpe/TODO @@ -0,0 +1,67 @@ +TODO LIST +--------- + +POW{cond}{P,M,Z} Fd, Fn, - power +RPW{cond}{P,M,Z} Fd, Fn, - reverse power +POL{cond}{P,M,Z} Fd, Fn, - polar angle (arctan2) + +LOG{cond}{P,M,Z} Fd, - logarithm to base 10 +LGN{cond}{P,M,Z} Fd, - logarithm to base e +EXP{cond}{P,M,Z} Fd, - exponent +SIN{cond}{P,M,Z} Fd, - sine +COS{cond}{P,M,Z} Fd, - cosine +TAN{cond}{P,M,Z} Fd, - tangent +ASN{cond}{P,M,Z} Fd, - arcsine +ACS{cond}{P,M,Z} Fd, - arccosine +ATN{cond}{P,M,Z} Fd, - 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]. -- cgit v1.2.3