mirrors/sqlite
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Changes to comments. In particular, a lengthy comment was added to encode.c

Browse Source 
that explains how the encoder algorithm works. (CVS 966)

FossilOrigin-Name: 8b388b2f690dbfd50eefc0fdede1c7785f78afa1
This commit is contained in:
drh 2003-05-10 03:36:53 +00:00
parent a3643a2697
commit 5fe2d8c913
5 changed files with 125 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
manifest
View File

@ -1,5 +1,5 @@
C Removed\snever-used\ssymbol\sSQLITE_ResultDetails.\s(CVS\s965)
D 2003-05-10T03:04:34
C Changes\sto\scomments.\s\sIn\sparticular,\sa\slengthy\scomment\swas\sadded\sto\sencode.c\r\nthat\sexplains\show\sthe\sencoder\salgorithm\sworks.\s(CVS\s966)
D 2003-05-10T03:36:54
F Makefile.in 004acec253ecdde985c8ecd5b7c9accdb210378f
F Makefile.linux-gcc b86a99c493a5bfb402d1d9178dcdc4bd4b32f906
F README f1de682fbbd94899d50aca13d387d1b3fd3be2dd
@ -20,14 +20,14 @@ F spec.template 238f7db425a78dc1bb7682e56e3834c7270a3f5e
F sqlite.1 83f4a9d37bdf2b7ef079a82d54eaf2e3509ee6ea
F sqlite.pc.in 30552343140c53304c2a658c080fbe810cd09ca2
F src/attach.c 7ebc7487de43e357a64226f8abef81f2669f2183
F src/auth.c 53b8923f17f364af84501fa99dc00c779913a26d
F src/auth.c c8f50d4507e37779d96ff3c55417bc2b612dfed6
F src/btree.c 077d75aee4ed63f3628698611ba43c87097d458d
F src/btree.h 23c50e00709de16a5dce1fcea9c0429cc955ff0e
F src/btree_rb.c 8e00e40be264716e1929987878672e55d9e0e76d
F src/build.c e24461d42381a36de88de6af06c03d9f14588705
F src/copy.c 44b13fd4d2444fb53bff8a5ecee1c5f6f86a8263
F src/delete.c f9536a75b444a21f11b7a1bc0fb8c876f691b013
F src/encode.c faf03741efe921755ec371cf4a6984536de00042
F src/encode.c ed720e54ec4ef4d4de651592f1dd1c74d422bbd2
F src/expr.c a666ef5220ca90ebcf40c8ccc783966a345a7616
F src/func.c 882c3ed5a02be18cd904715c7ec62947a34a3605
F src/hash.c 4fc39feb7b7711f6495ee9f2159559bedb043e1f
@ -59,7 +59,7 @@ F src/trigger.c 8ee811986080de60d9d883ad96daffea82014f27
F src/update.c dc3b680b4cf2cb6d839950b68d632850746639b9
F src/util.c 87635cfdfffa056a8d3147719357aa442374f78c
F src/vacuum.c 14ac3073203fa021e01ffe33db56968ad79a8344
F src/vdbe.c 829fa31c2169588db7a041950cb95c6bb75811a6
F src/vdbe.c e9e560b0c568fb4ffb189d3e0d91628a33d2a367
F src/vdbe.h 985c24f312d10f9ef8f9a8b8ea62fcdf68e82f21
F src/where.c ef11773a07cf075740378d7d1cbabf328146fdc9
F test/all.test 569a92a8ee88f5300c057cc4a8f50fbbc69a3242
@ -165,7 +165,7 @@ F www/speed.tcl cb4c10a722614aea76d2c51f32ee43400d5951be
F www/sqlite.tcl 4bd1729e320f5fa9125f0022b281fbe839192125
F www/tclsqlite.tcl 1db15abeb446aad0caf0b95b8b9579720e4ea331
F www/vdbe.tcl 2013852c27a02a091d39a766bc87cff329f21218
P bf558e79524c04339f1174dc935e39d47cb33457
R dbcdc1e6ba937154b079e14cdd4eab7b
U jplyon
Z c717a1a241516bca947b8579016988c0
P 26bd7bb1779e14f19c00e450aaa9529f2aabf131
R b680c0a504530ce6590f8a3af4ddd816
U drh
Z d87b54e38f0dd3d4af38249efc6d41d2

2
manifest.uuid
View File

@ -1 +1 @@
26bd7bb1779e14f19c00e450aaa9529f2aabf131
8b388b2f690dbfd50eefc0fdede1c7785f78afa1

32
src/auth.c
View File

@ -14,7 +14,7 @@
** systems that do not need this facility may omit it by recompiling
** the library with -DSQLITE_OMIT_AUTHORIZATION=1
**
** $Id: auth.c,v 1.9 2003/05/02 14:32:13 drh Exp $
** $Id: auth.c,v 1.10 2003/05/10 03:36:54 drh Exp $
*/
#include "sqliteInt.h"
@ -28,15 +28,35 @@
** Set or clear the access authorization function.
**
** The access authorization function is be called during the compilation
** phase to verify that the user has read and/or write access permission
** phase to verify that the user has read and/or write access permission on
** various fields of the database. The first argument to the auth function
** is a copy of the 3rd argument to this routine. The second argument
** to the auth function is one of these constants:
**
** SQLITE_READ_COLUMN
** SQLITE_WRITE_COLUMN
** SQLITE_DELETE_ROW
** SQLITE_INSERT_ROW
** SQLITE_COPY
** SQLITE_CREATE_INDEX
** SQLITE_CREATE_TABLE
** SQLITE_CREATE_TEMP_INDEX
** SQLITE_CREATE_TEMP_TABLE
** SQLITE_CREATE_TEMP_TRIGGER
** SQLITE_CREATE_TEMP_VIEW
** SQLITE_CREATE_TRIGGER
** SQLITE_CREATE_VIEW
** SQLITE_DELETE
** SQLITE_DROP_INDEX
** SQLITE_DROP_TABLE
** SQLITE_DROP_TEMP_INDEX
** SQLITE_DROP_TEMP_TABLE
** SQLITE_DROP_TEMP_TRIGGER
** SQLITE_DROP_TEMP_VIEW
** SQLITE_DROP_TRIGGER
** SQLITE_DROP_VIEW
** SQLITE_INSERT
** SQLITE_PRAGMA
** SQLITE_READ
** SQLITE_SELECT
** SQLITE_TRANSACTION
** SQLITE_UPDATE
**
** The third and fourth arguments to the auth function are the name of
** the table and the column that are being accessed. The auth function

82
src/encode.c
View File

@ -15,10 +15,90 @@
** data in an SQLite database. The code in this file is not used by any other
** part of the SQLite library.
**
** $Id: encode.c,v 1.5 2003/01/19 03:59:46 drh Exp $
** $Id: encode.c,v 1.6 2003/05/10 03:36:54 drh Exp $
*/
#include <string.h>
/*
** How This Encoder Works
**
** The output is allowed to contain any character except 0x27 (') and
** 0x00. This is accomplished by using an escape character to encode
** 0x27 and 0x00 as a two-byte sequence. The escape character is always
** 0x01. An 0x00 is encoded as the two byte sequence 0x01 0x01. The
** 0x27 character is encoded as the two byte sequence 0x01 0x03. Finally,
** the escape character itself is encoded as the two-character sequence
** 0x01 0x02.
**
** To summarize, the encoder works by using an escape sequences as follows:
**
** 0x00 -> 0x01 0x01
** 0x01 -> 0x01 0x02
** 0x27 -> 0x01 0x03
**
** If that were all the encoder did, it would work, but in certain cases
** it could double the size of the encoded string. For example, to
** encode a string of 100 0x27 character would require 100 instances of
** the 0x01 0x03 escape sequence resulting in a 200-character output.
** We would prefer to keep the size of the encoded string smaller than
** this.
**
** To minimize the encoding size, we first add a fixed offset value to each
** byte in the sequence. The addition is module 256. (That is to say, if
** the sum of the original character value and the offset exceeds 256, then
** the higher order bits are truncated.) The offset is chosen to minimize
** the number of characters in the string that need to be escaped. For
** example, in the case above where the string was composed of 100 0x27
** characters, the offset might be 0x01. Each of the 0x27 characters would
** then be converted into an 0x28 character which would not need to be
** escaped at all and so the 100 character input string would be converted
** into just 100 characters of output. Actually 101 characters of output -
** we have to record the offset used as the first byte in the sequence so
** that the string can be decoded. Since the offset value is stored as
** part of the output string and the output string is not allowed to contain
** characters 0x00 or 0x27, the offset cannot be 0x00 or 0x27.
**
** Here, then, are the encoding steps:
**
** (1) Choose an offset value and make it the first character of
** output.
**
** (2) Copy each input character into the output buffer, one by
** one, adding the offset value as you copy.
**
** (3) If the value of an input character plus offset is 0x00, replace
** that one character by the two-character sequence 0x01 0x01.
** If the sum is 0x01, replace it with 0x01 0x02. If the sum
** is 0x27, replace it with 0x01 0x03.
**
** (4) Put a 0x00 terminator at the end of the output.
**
** Decoding is obvious:
**
** (5) Copy encoded characters except the first into the decode
** buffer. Set the first encoded character aside for use as
** the offset in step 7 below.
**
** (6) Convert each 0x01 0x01 sequence into a single character 0x00.
** Convert 0x01 0x02 into 0x01. Convert 0x01 0x03 into 0x27.
**
** (7) Subtract the offset value that was the first character of
** the encoded buffer from all characters in the output buffer.
**
** The only tricky part is step (1) - how to compute an offset value to
** minimize the size of the output buffer. This is accomplished to testing
** all offset values and picking the one that results in the fewest number
** of escapes. To do that, we first scan the entire input and count the
** number of occurances of each character value in the input. Suppose
** the number of 0x00 characters is N(0), the number of occurances of 0x01
** is N(1), and so forth up to the number of occurances of 0xff is N(256).
** An offset of 0 is not allowed so we don't have to test it. The number
** of escapes required for an offset of 1 is N(1)+N(2)+N(40). The number
** of escapes required for an offset of 2 is N(2)+N(3)+N(41). And so forth.
** In this way we find the offset that gives the minimum number of escapes,
** and thus minimizes the length of the output string.
*/
/*
** Encode a binary buffer "in" of size n bytes so that it contains
** no instances of characters '\'' or '\000'. The output is

16
src/vdbe.c
View File

@ -36,7 +36,7 @@
** in this file for details. If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.221 2003/05/02 14:32:14 drh Exp $
** $Id: vdbe.c,v 1.222 2003/05/10 03:36:54 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>
@ -3453,10 +3453,10 @@ case OP_OpenWrite: {
/* Opcode: OpenTemp P1 P2 *
**
** Open a new cursor that points to a table or index in a temporary
** database file. The temporary file is opened read/write even if
** the main database is read-only. The temporary file is deleted
** when the cursor is closed.
** Open a new cursor to a transient table.
** The transient cursor is always opened read/write even if
** the main database is read-only. The transient table is deleted
** automatically when the cursor is closed.
**
** The cursor points to a BTree table if P2==0 and to a BTree index
** if P2==1. A BTree table must have an integer key and can have arbitrary
@ -3464,7 +3464,7 @@ case OP_OpenWrite: {
**
** This opcode is used for tables that exist for the duration of a single
** SQL statement only. Tables created using CREATE TEMPORARY TABLE
** are opened using OP_OpenAux or OP_OpenWrAux. "Temporary" in the
** are opened using OP_OpenRead or OP_OpenWrite. "Temporary" in the
** context of this opcode means for the duration of a single SQL statement
** whereas "Temporary" in the context of CREATE TABLE means for the duration
** of the connection to the database. Same word; different meanings.
@ -3997,8 +3997,8 @@ case OP_Delete: {
/* Opcode: KeyAsData P1 P2 *
**
** Turn the key-as-data mode for cursor P1 either on (if P2==1) or
** off (if P2==0). In key-as-data mode, the Field opcode pulls
** data off of the key rather than the data. This is useful for
** off (if P2==0). In key-as-data mode, the OP_Column opcode pulls
** data off of the key rather than the data. This is used for
** processing compound selects.
*/
case OP_KeyAsData: {