Sorry Roger. I forgot pointer arithmatic. BTW I think hardware crc32 can also be used in J64. What will be its downside apart from higer chance of getting collison when compared to crc64?
Ср, 30 июл 2014, Roger Hui написал(а): > Actually, no. z would be declared to be a pointer of the appropriate type > and z=z+1; would make z point to the next item. > > z=z+sizeof(*z); would in fact be wrong. For example, if z points to a > 4-byte integer, sizeof(*z) would be 4 and z=z+sizeof(*z); would make z > point to 4 items further. You can verify this by writing and running a > short C program or by rummaging around in a C debugger. > > > > > On Wed, Jul 30, 2014 at 7:05 PM, bill lam <[email protected]> wrote: > > > Sorry for being meticulous, the last step probably better be expressed as > > z=z+sizeof(*z) > > On Jul 31, 2014 12:37 AM, "Roger Hui" <[email protected]> wrote: > > > > > Thanks for your comments and questions. > > > > > > 0. The C code presented is only for a primitive datatype (in C). The > > paper > > > (script) says this. The basic hashing logic still works for other > > > datatypes, but instead of using == and != (the C equals and not-equal) > > > you'd need something more elaborate. Still simple conceptually because > > in > > > your head you can subsume the details by thinking "match" or "not match". > > > > > > 1. The APL\360 defn assumes that the left argument is a vector. The > > > "anomaly" you found only occurs if the left argument is not a vector. > > > > > > 2. *z++=*h<0?xn:*h; is equivalent to: > > > > > > blah= *h<0 ? xn : *h; // if *h is less than 0 then xn, otherwise *h > > > *z=blah; // set the location pointed to by z, to blah > > > z=z+1; // increment the pointer z by 1 > > > > > > This is standard C. In that context the statement is also equivalent to > > > z[i]=*h<0?xn:*h; > > > > > > > > > > > > On Wed, Jul 30, 2014 at 8:53 AM, Brian Schott <[email protected]> > > > wrote: > > > > > > > Roger, > > > > > > > > Because my C is so weak I could use some explanation in words of what > > > the C > > > > is doing, not in general, but to discuss the questions below. > > > > > > > > Would you say that the basic approach that is being taken in DO's is > > more > > > > like the APL\360 definition or more like the Extended definition. I > > > guess I > > > > am a little surprised that a Loop is required through both the x and > > the > > > y > > > > values. In the Dictionary entry for Index of is the following example, > > > > where the y component is not an atom, but a string. Is that a typical > > > case > > > > for which y must be looped through as well as x? I thought maybe the > > > answer > > > > was yes, and tried. > > > > > > > > A=: 'abcdefghijklmnopqrstuvwxyz' > > > > m=: 5 4 $ 12{. A > > > > m;(m i. 'efgh');(1{m);(4{m) > > > > > > > > I then found a slight "anomaly" though, trying the APL\360 definition > > > with > > > > that example. > > > > > > > > > > > > +/*./\m~:/'efgh' > > > > 1 5 5 5 > > > > 5 1 5 5 > > > > 5 5 1 5 > > > > 5 5 5 1 > > > > > > > > However that "anomaly" was fixed by the Extended definition, so maybe > > > > therein is an example of why the y value must be looped through, too. > > > > > > > > +/*./\m~:/&:<"(_1+#$m)'efgh' > > > > 1 > > > > > > > > Can you comment, please? > > > > > > > > Also, in the second DO there is a phrase like this: *z++=*h<0?xn:*h; > > > > > > > > I am familiar with the B?T:F part of the phrase, but I have never seen > > a > > > ++ > > > > followed by an assignment. Does that just add one to the result from > > the > > > > assigned amount? > > > > > > > > Oh, and thanks for posting your paper. > > > > > > > > > > > > -- > > > > (B=) > > > > ---------------------------------------------------------------------- > > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > > > ---------------------------------------------------------------------- > > > For information about J forums see http://www.jsoftware.com/forums.htm > > > > > ---------------------------------------------------------------------- > > For information about J forums see http://www.jsoftware.com/forums.htm > > > ---------------------------------------------------------------------- > For information about J forums see http://www.jsoftware.com/forums.htm -- regards, ==================================================== GPG key 1024D/4434BAB3 2008-08-24 gpg --keyserver subkeys.pgp.net --recv-keys 4434BAB3 gpg --keyserver subkeys.pgp.net --armor --export 4434BAB3 ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
