Custom Search

Based on kernel version `4.0`. Page generated on `2015-04-14 21:19 EST`.

1 TODO LIST 2 --------- 3 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) 7 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 17 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. 22 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. 28 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. 35 36 Rounding Methods 37 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. 43 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. 49 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. 54 55 [NOTE: pulled out from some docs on ARM floating point, specifically 56 for the Acorn FPE, but not limited to it: 57 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. 64 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].

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.