java - Mapping Unique 16-Digit numeric ID to Unique Alphanumeric ID -

-

in project i'm working on, need generate 16 character long unique ids, consisting of 10 numbers plus 26 uppercase letters (only uppercase). must guaranteed universally unique, 0 chance of repeat ever.

the ids not stored forever. id thrown out of database after period of time , new unique id must generated. ids can never repeat thrown out ones either.

so randomly generating 16 digits , checking against list of generated ids not option because there no comprehensive list of previous ids. also, uuid not work because ids must 16 digits in length.

right i'm using 16-digit unique ids, guaranteed universally unique every time they're generated (i'm using timestamps generate them plus unique server id). however, need ids difficult predict, , using timestamps makes them easy predict.

so need map 16 digit numeric ids have larger range of 10 digits + 26 letters without losing uniqueness. need sort of hashing function maps smaller range larger range, guaranteeing one-to-one mapping unique ids guaranteed stay unique after being mapped.

i have searched , far have not found hashing or mapping functions guaranteed collision-free, 1 must exist if i'm mapping larger space. suggestions appreciated.

brandon staggs wrote article on implementing partial serial number verification system. examples written in delphi, converted other languages.


Comments

Post a Comment

Popular posts from this blog

matlab - error with cyclic autocorrelation function -

-
Image
i'm trying code cyclic autocorrelation function in matlab follows: t=0:(n-1); t=t*te; i_alpha=0; tau=-n2*te:te:n2*te; alpha=-1/2:1/n:1/2; ryy_cl=zeros(length(alpha),length(tau)); alpha=alpha/te ind_tau=0; i_alpha=i_alpha+1; k=tau ind_tau=ind_tau+1; if k>0 % ryy_cl(i_alpha,ind_tau)=1/length(sig_bin_syl_mod(1:end- k))*sum((sig_bin_syl_mod(1:end-k)).*sig_bin_syl_mod(k+1:end)).*exp(1i*2*pi*alpha*t(1+k:length(sig_bin_syl_mod(1:end)))); ryy_cl(i_alpha,ind_tau)=(1/n)*sum((sig_bin_syl_mod(1:end-k)).*sig_bin_syl_mod(k+1:end)).*exp(-1i*2*pi*alpha*t(1:end-k)); else ryy_cl(i_alpha,ind_tau)=(1/n)*sum((sig_bin_syl_mod(1-k:end)).*sig_bin_syl_mod(1:end+k)).*exp(-1i*2*pi*alpha*t(1-k:end)); end end end i'm getting errors, , doesn't show expecting. according below formulae, how can fix it? the code provided incomplete, difficult confidently reproduce error. in particular, haven't de...
Read more

django - (fields.E300) Field defines a relation with model 'AbstractEmailUser' which is either not installed, or is abstract -

-
i trying create customuser django project email username , add radio button truck , company. in registration process email-id registered per truck or company. mentioned radio button 'tag' , add manytomany field tag in emailuser model. when makemigrations, raising error : (fields.e300) field defines relation model 'abstractemailuser' either not installed, or abstract. i quite new django , not sure whether have created correct code wants. please me solving this. here code, models.py: import django django.contrib.auth.models import ( abstractbaseuser, baseusermanager, permissionsmixin) django.core.mail import send_mail django.db import models django.utils import timezone django.utils.translation import ugettext_lazy _ class emailusermanager(baseusermanager): """custom manager emailuser.""" def _create_user(self, email, password, is_staff, is_superuser, **extra_fields): """create , save emailus...
Read more

c# - What is a good .Net RefEdit control to use with ExcelDna? -

-
i using exceldna , c# build suite of tools. part of forms i'd want user select cells/ranges workbook. i've got application.inputbox route working...but doesn't cool... i haven't read many things excel's refedit control, , see many have in past written workarounds, in (shudder) vba or vb.net. however, none of these seem recent... best approach/control refedit functionality on form run via exceldna (if applicable)? the refedit sample project of github explores different ways of dealing threading when showing form excel add-in, main issue making refedit control .net add-in. check page links various other implementations: https://github.com/excel-dna/exceldna/wiki/links-about-refedit
Read more