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author | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-16 12:21:41 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-07-16 12:21:41 -0700 |
commit | c309b6f24222246c18a8b65d3950e6e755440865 (patch) | |
tree | 11893170f5c246bb0dee8066e85878af04162ab0 /Documentation/arm/nwfpe/todo.rst | |
parent | 3e859477a1db52a0435d06a55fdb54f62d69c292 (diff) | |
parent | 168869492e7009b6861b615f1d030c99bc805e83 (diff) | |
download | linux-stable-c309b6f24222246c18a8b65d3950e6e755440865.tar.gz linux-stable-c309b6f24222246c18a8b65d3950e6e755440865.tar.bz2 linux-stable-c309b6f24222246c18a8b65d3950e6e755440865.zip |
Merge tag 'docs/v5.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
Pull rst conversion of docs from Mauro Carvalho Chehab:
"As agreed with Jon, I'm sending this big series directly to you, c/c
him, as this series required a special care, in order to avoid
conflicts with other trees"
* tag 'docs/v5.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (77 commits)
docs: kbuild: fix build with pdf and fix some minor issues
docs: block: fix pdf output
docs: arm: fix a breakage with pdf output
docs: don't use nested tables
docs: gpio: add sysfs interface to the admin-guide
docs: locking: add it to the main index
docs: add some directories to the main documentation index
docs: add SPDX tags to new index files
docs: add a memory-devices subdir to driver-api
docs: phy: place documentation under driver-api
docs: serial: move it to the driver-api
docs: driver-api: add remaining converted dirs to it
docs: driver-api: add xilinx driver API documentation
docs: driver-api: add a series of orphaned documents
docs: admin-guide: add a series of orphaned documents
docs: cgroup-v1: add it to the admin-guide book
docs: aoe: add it to the driver-api book
docs: add some documentation dirs to the driver-api book
docs: driver-model: move it to the driver-api book
docs: lp855x-driver.rst: add it to the driver-api book
...
Diffstat (limited to 'Documentation/arm/nwfpe/todo.rst')
-rw-r--r-- | Documentation/arm/nwfpe/todo.rst | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/Documentation/arm/nwfpe/todo.rst b/Documentation/arm/nwfpe/todo.rst new file mode 100644 index 000000000000..393f11b14540 --- /dev/null +++ b/Documentation/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. |