About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / arm / nwfpe / TODO

Custom Search

Based on kernel version 3.13. Page generated on 2014-01-20 22:00 EST.

2	---------
4	POW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - power
5	RPW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse power
6	POL{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - polar angle (arctan2)
8	LOG{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base 10
9	LGN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base e 
10	EXP{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - exponent
11	SIN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - sine
12	COS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - cosine
13	TAN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - tangent
14	ASN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arcsine
15	ACS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arccosine
16	ATN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arctangent
18	These are not implemented.  They are not currently issued by the compiler,
19	and are handled by routines in libc.  These are not implemented by the FPA11
20	hardware, but are handled by the floating point support code.  They should 
21	be implemented in future versions.
23	There are a couple of ways to approach the implementation of these.  One
24	method would be to use accurate table methods for these routines.  I have 
25	a couple of papers by S. Gal from IBM's research labs in Haifa, Israel that
26	seem to promise extreme accuracy (in the order of 99.8%) and reasonable speed.
27	These methods are used in GLIBC for some of the transcendental functions.
29	Another approach, which I know little about is CORDIC.  This stands for
30	Coordinate Rotation Digital Computer, and is a method of computing 
31	transcendental functions using mostly shifts and adds and a few
32	multiplications and divisions.  The ARM excels at shifts and adds,
33	so such a method could be promising, but requires more research to 
34	determine if it is feasible.
36	Rounding Methods
38	The IEEE standard defines 4 rounding modes.  Round to nearest is the
39	default, but rounding to + or - infinity or round to zero are also allowed.
40	Many architectures allow the rounding mode to be specified by modifying bits
41	in a control register.  Not so with the ARM FPA11 architecture.  To change
42	the rounding mode one must specify it with each instruction.
44	This has made porting some benchmarks difficult.  It is possible to
45	introduce such a capability into the emulator.  The FPCR contains 
46	bits describing the rounding mode.  The emulator could be altered to 
47	examine a flag, which if set forced it to ignore the rounding mode in
48	the instruction, and use the mode specified in the bits in the FPCR.
50	This would require a method of getting/setting the flag, and the bits
51	in the FPCR.  This requires a kernel call in ArmLinux, as WFC/RFC are
52	supervisor only instructions.  If anyone has any ideas or comments I
53	would like to hear them.
55	[NOTE: pulled out from some docs on ARM floating point, specifically
56	 for the Acorn FPE, but not limited to it:
58	 The floating point control register (FPCR) may only be present in some
59	 implementations: it is there to control the hardware in an implementation-
60	 specific manner, for example to disable the floating point system.  The user
61	 mode of the ARM is not permitted to use this register (since the right is
62	 reserved to alter it between implementations) and the WFC and RFC
63	 instructions will trap if tried in user mode.
65	 Hence, the answer is yes, you could do this, but then you will run a high
66	 risk of becoming isolated if and when hardware FP emulation comes out
67			-- Russell].
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.