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Diffstat (limited to 'sql/sql_acl_getsort.ic')
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diff --git a/sql/sql_acl_getsort.ic b/sql/sql_acl_getsort.ic new file mode 100644 index 00000000..df55c7c5 --- /dev/null +++ b/sql/sql_acl_getsort.ic @@ -0,0 +1,205 @@ +/* Copyright (c) 2019, MariaDB Corporation. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; version 2 of the License. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */ + +#ifndef NO_EMBEDDED_ACCESS_CHECKS +/* + Returns a number which, if sorted in descending order, magically puts + patterns in the order from most specific (e.g. no wildcards) to most generic + (e.g. "%"). That is, the larger the number, the more specific the pattern is. + + Takes a template that lists types of following patterns (by the first letter + of _h_ostname, _d_bname, _u_sername) and up to four patterns. + No more than two can be of 'h' or 'd' type (because one magic value takes 26 + bits, see below). + + ======================================================================== + + Here's how the magic is created: + + Let's look at one iteration of the for() loop. That's one pattern. With + wildcards (usernames aren't interesting). + + By definition a pattern A is "more specific" than pattern B if the set of + strings that match the pattern A is smaller than the set of strings that + match the pattern B. Strings are taken from the big superset of all valid + utf8 strings up to the maxlen. + + Strings are matched character by character. For every non-wildcard + character there can be only one matching character in the matched string. + + For a wild_one character ('_') any valid utf8 character will do. Below + numchars would mean a total number of vaid utf8 characters. It's a huge + number. A number of matching strings for wild_one will be numchars. + + For a wild_many character ('%') any number of valid utf8 characters will do. + How many string will match it depends on the amount of non-wild_many + characters. Say, if a number of non-wildcard characters is N, and a number + of wild_one characters is M, and the number of wild_many characters is K, + then for K=1 its wild_many character will match any number of valid utf8 + characters from 0 to L=maxlen-N-M. The number of matching strings will be + + 1 + numchars + numchars^2 + numchars^3 + ... + numchars^L + + Intermediate result: if M=K=0, the pattern will match only one string, + if M>0, K=0, the pattern will match numchars^M strings, if K=1, the + pattern will match + + numchars^M + 1 + numchars + numchars^2 + ... + numchars^L + + For a more visual notation, let's write these huge numbers not as + decimal or binary, but base numchars. Then the last number will be + a sum of two numbers: the first is one followed by M zeros, the second + constists of L+1 ones: + + 1000{...M...}000 + 111{...L+1...}1111 + + This could produce any of the following + + 111...112111...1111 if L > M, K = 1 + 100...001111...1111 if M > L, K = 1 + 2111111...111111111 if M = L, K = 1 + 1111111...111111111 if M = 0, K = 1 + 1000000...000000000 if K = 0, M > 0 + + There are two complications caused by multiple wild_many characters. + For, say, two wild_many characters, either can accept any number of utf8 + characters, as long the the total amount of them is less then or equal to L. + Same logic applies to any number of non-consequent wild_many characters + (consequent wild_many characters count as one). This gives the number of + matching strings of + + 1 + F(K,1)*numchars + F(K,2)*numchars^2 + ... + F(K,L)*numchars^L + + where F(K,R) is the "number of ways one can put R balls into K boxes", + that is C^{K-1}_{R+K-1}. + + In the "base numchars" notation, it means that besides 0, 1, and 2, + an R-th digit can be F(K,R). For the purpose of comparison, we only need + to know the most significant digit, F(K, L). + While it can be huge, we don't need the exact value, it's a + a monotonously increasing function of K, so if K1>K2, F(K1,L) > F(K2,L) + and we can simply compare values of K instead of complex F(K,L). + + The second complication: F(K,R) gives only an upper boundary, the + actual number of matched strings can be smaller. + Example: pattern "a%b%c" can match "abbc" as a(b)b()c, and as a()b(b)c. + F(2,1) = 2, but it's only one string "abbc". + We'll ignore it here under assumption that it almost never happens + in practice and this simplification won't noticeably disrupt the ordering. + + The last detail: old get_sort function sorted by the non-wildcard prefix + length, so in "abc_" and "a_bc" the former one was sorted first. Strictly + speaking they're both equally specific, but to preserve the backward + compatible sorting we'll use the P "prefix length or 0 if no wildcards" + to break ties. + + Now, let's compare two long numbers. Numbers are easy to compare, + the longer number is larger. If they both have the same lengths, + the one with the larger first digit is larger, and so on. + + But there is no need to actually calculate these numbers. + Three numbers L, K, M (and P to break ties) are enough to describe a pattern + for a purpose of comparison. L/K/M triplets can be compared like this: + + * case 1: if for both patterns L>M: compare L, K, M, in that order + because: + - if L1 > L2, the first number is longer + - If L1 == L2, then the first digit is a monotonously increasing function + of K, so the first digit is larger when K is larger + - if K1 == K2, then all other digits in these numbers would be the + same too, with the exception of one digit in the middle that + got +1 because of +1000{...M...}000. So, whatever number has a + larger M will get this +1 first. + * case 2: if for both patterns L<M: compare M, L, K, in that order + * case 3: if for both patterns L=M: compare L (or M), K + * case 4: if one L1>M1, other L2=M2: compare L, K, M + * case 5: if one L1<M1, other L2=M2: compare M, L, K + * case 6: if one pattern L1>M1, the other M2>L2: first is more generic + unless (case 6a) K1=K2=1,M1=0,M2=L2+1 (in that case - equal) + + note that in case 3 one can use a rule from the case either 1 or 2, + in the case 4 one can use the rule from the case 1, + in the case 5 one can use the rule from the case 2. + + for the case 6 and ignoring the special case 6a, to compare patterns by a + magic number as a function z(a,b,c), we must ensure that z(L1,K1,M1) is + greater than z(M2,L2,K2) when L1=M2. This can be done by an extra bit, + which is 1 for K and 0 for L. Thus, the magic number could be + + case 1: (((L*2 + 1)*(maxlen+1) + K)*(maxlen+1) + M)*(maxlen+1) + P + case 2: ((M*2*(maxlen+1) + L)*(maxlen+1) + K)*(maxlen+1) + P + + upper bound: L<=maxlen, M<=maxlen, K<=maxlen/2, P<maxlen + for a current maxlen=64, the magic number needs 26 bits. +*/ + +static ulonglong get_magic_sort(const char *templ, ...) +{ + ulonglong sort=0; + va_list args; + va_start(args, templ); + + IF_DBUG(uint bits_used= 0,); + + for (; *templ; templ++) + { + char *pat= va_arg(args, char*); + + if (*templ == 'u') + { + /* Username. Can be empty (= anybody) or a literal. Encoded in one bit */ + sort= (sort << 1) + !*pat; + IF_DBUG(bits_used++,); + continue; + } + + /* A wildcard pattern. Encoded in 26 bits. */ + uint maxlen= *templ == 'd' ? max_dbname_length : max_hostname_length; + DBUG_ASSERT(maxlen <= 64); + DBUG_ASSERT(*templ == 'd' || *templ == 'h'); + + uint N= 0, M= 0, K= 0, P= 0; + for (uint i=0; pat[i]; i++) + { + if (pat[i] == wild_many) + { + if (!K && !M) P= N; + K++; + while (pat[i+1] == wild_many) i++; + continue; + } + if (pat[i] == wild_one) + { + if (!K && !M) P= N; + M++; + continue; + } + if (pat[i] == wild_prefix && pat[i+1]) i++; + N++; + } + uint L= K ? maxlen - N - M : 0, d= maxlen + 1, magic; + if (L > M) + magic= (((L * 2 + 1) * d + K) * d + M) * d + P; + else + magic= (((M * 2 + 0) * d + L) * d + K) * d + P; + DBUG_ASSERT(magic < 1<<26); + sort= (sort << 26) + magic; + IF_DBUG(bits_used+= 26,); + } + DBUG_ASSERT(bits_used < 8*sizeof(sort)); + va_end(args); + return ~sort; +} +#endif |