Ali Çehreli wrote: > Jérôme M. Berger wrote: >> Ali Çehreli wrote: >>> � wrote: >>> >>>> The idea is to build a value that is between minA and maxA and will >>>> set as many bits as possible when or'ed with maxB: >>> The assumption that maxB would be the value that produces the maximum >>> a|b is not correct. A lower valued b may fill more gaps in the bit >>> representation of what is calculated from min_a and max_a. >>> >>> Your function failed for me with the following values: >>> >>> min_a 00000000000000000000000011001000 000000c8 200 >>> max_a 00000000000000000000001100001111 0000030f 783 >>> min_b 00000000000000000000000001000101 00000045 69 >>> max_b 00000000000000000000001001100001 00000261 609 >>> calculated 00000000000000000000001001100101 00000265 613 >>> WRONG! empirical 00000000000000000000001111111111 000003ff 1023 >>> emp_max_a 00000000000000000000000110011110 0000019e 414 >>> emp_max_b 00000000000000000000001001100001 00000261 609 >>> >>> Please see my test code elsewhere in the same thread: :) >>> >>> > http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=108851 > >>> >> The "calculated" value above obviously was not computed with my >> function! > > My mistake: It was your function but the highbit() that I used was not > correct. The one I used was returning the *value* of the highest bit. > >> Since the return value from my function includes maxA and >> maxB, at least all bits that are set in either of those should be >> set in the output. >> >> I've run my code with those input and the result is 3ff as >> expected... (See attached source file). > > Perhaps my test code is wrong; but I can't find my error. :/ > > Your function reports 0b_111 for these set of values: > > min_a = 5; > max_a = 6; > min_b = 4; > max_b = 4; > > But the maximum value of a|b is 6. > Yes, like I said with my code, it is conservative. It will give the optimal result for over 99% of the cases but give a slightly higher value for the rest. I'll post a new version that's 100% precise in a few minutes.
Jerome
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