On Wed, 19 Apr 2006, Rusty Scott wrote: >On Wed, 2006-04-19 at 08:49 +0200, christophpfister at bluemail.ch wrote: >> Sorry to have concurrenced you, but manu told me to create one. Anyway, the >> error (not the accurancy!!) is now < 0.047%. >> >Not really a concurrence, because yours is a log base2 where mine is a >log base 10. (Actually a 10*log10 for use in dB calcaulations) Now you >have a place to put your function when it is ready (if my patch is >ack'd) and we could eventually base the log10 calculations on the log2 >functions with the appropriate conversion factor. Christoph's code has a log10 function that does just that, returning the log10 in 4.24 fixed-point. It's much more accurate than Jack Kelliher's code to do the same thing. Still, I can do even better: This is for log base 10 over the range 1 to 2^24 Author Max % error Max abs error CPU Time ------------------------------------------------------ Jack 0.844475% 0.0211893 19.08 Christoph 0.0462607% 0.00179902 6.66 Trent 256 0.000136763% 0.00000682604 7.74 Trent 128 0.000216441% 0.00000729513 7.75 Trent 64 0.000646134% 0.0000160004 7.77 Trent 32 0.00276062% 0.0000546169 7.74 Jack's code uses two tables, one with 200 32-bit values and another with 9 32-bit values. Christoph's code uses two tables, one with 256 8-bit values and another with 256 16-bit values. The four versions of my code uses a single table with 256, 128, 64, or 32 16-bit values, respectively. Even with a lookup table one eighth the size, my code is still twenty times more accurate. Here is a graph of the relative error over the range 0-64k: http://www.speakeasy.org/~xyzzy/log10.png _______________________________________________ linux-dvb@xxxxxxxxxxx http://www.linuxtv.org/cgi-bin/mailman/listinfo/linux-dvb
