1 TODO LIST
2 =========
3
4 ::
5
6 POW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - power
7 RPW{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - reverse power
8 POL{cond}<S|D|E>{P,M,Z} Fd, Fn, <Fm,#value> - polar angle (arctan2)
9
10 LOG{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base 10
11 LGN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - logarithm to base e
12 EXP{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - exponent
13 SIN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - sine
14 COS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - cosine
15 TAN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - tangent
16 ASN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arcsine
17 ACS{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arccosine
18 ATN{cond}<S|D|E>{P,M,Z} Fd, <Fm,#value> - arctangent
19
20 These are not implemented. They are not currently issued by the compiler,
21 and are handled by routines in libc. These are not implemented by the FPA11
22 hardware, but are handled by the floating point support code. They should
23 be implemented in future versions.
24
25 There are a couple of ways to approach the implementation of these. One
26 method would be to use accurate table methods for these routines. I have
27 a couple of papers by S. Gal from IBM's research labs in Haifa, Israel that
28 seem to promise extreme accuracy (in the order of 99.8%) and reasonable speed.
29 These methods are used in GLIBC for some of the transcendental functions.
30
31 Another approach, which I know little about is CORDIC. This stands for
32 Coordinate Rotation Digital Computer, and is a method of computing
33 transcendental functions using mostly shifts and adds and a few
34 multiplications and divisions. The ARM excels at shifts and adds,
35 so such a method could be promising, but requires more research to
36 determine if it is feasible.
37
38 Rounding Methods
39 ----------------
40
41 The IEEE standard defines 4 rounding modes. Round to nearest is the
42 default, but rounding to + or - infinity or round to zero are also allowed.
43 Many architectures allow the rounding mode to be specified by modifying bits
44 in a control register. Not so with the ARM FPA11 architecture. To change
45 the rounding mode one must specify it with each instruction.
46
47 This has made porting some benchmarks difficult. It is possible to
48 introduce such a capability into the emulator. The FPCR contains
49 bits describing the rounding mode. The emulator could be altered to
50 examine a flag, which if set forced it to ignore the rounding mode in
51 the instruction, and use the mode specified in the bits in the FPCR.
52
53 This would require a method of getting/setting the flag, and the bits
54 in the FPCR. This requires a kernel call in ArmLinux, as WFC/RFC are
55 supervisor only instructions. If anyone has any ideas or comments I
56 would like to hear them.
57
58 NOTE:
59 pulled out from some docs on ARM floating point, specifically
60 for the Acorn FPE, but not limited to it:
61
62 The floating point control register (FPCR) may only be present in some
63 implementations: it is there to control the hardware in an implementation-
64 specific manner, for example to disable the floating point system. The user
65 mode of the ARM is not permitted to use this register (since the right is
66 reserved to alter it between implementations) and the WFC and RFC
67 instructions will trap if tried in user mode.
68
69 Hence, the answer is yes, you could do this, but then you will run a high
70 risk of becoming isolated if and when hardware FP emulation comes out
71
72 -- Russell.
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