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Alternative implementation of the comparison opcode speed-up of

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check-in [4a8805d9a66dc888] that should pass muster with UBSAN.

FossilOrigin-Name: afb18f64541effaeaada2d72c7c91adfe5ec3e2b1418c0bc281083125fb5badb
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drh
2021-03-28 23:37:56 +00:00
parent 9cffb0ffb9
commit 1af3fd562f
5 changed files with 45 additions and 17 deletions
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30
src/global.c
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@@ -37,7 +37,7 @@ const unsigned char sqlite3UpperToLower[] = {
198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,
216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,
234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,
252,253,254,255
252,253,254,255,
#endif
#ifdef SQLITE_EBCDIC
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, /* 0x */
@@ -57,7 +57,35 @@ const unsigned char sqlite3UpperToLower[] = {
224,225,162,163,164,165,166,167,168,169,234,235,236,237,238,239, /* Ex */
240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255, /* Fx */
#endif
/* All of the upper-to-lower conversion data is above. The following
** 18 integers are completely unrelated. They are appended to the
** sqlite3UpperToLower[] array to avoid UBSAN warnings. Here's what is
** going on:
**
** The SQL comparison operators (<>, =, >, <=, <, and >=) are implemented
** by invoking sqlite3MemCompare(A,B) which compares values A and B and
** returns negative, zero, or positive if A is less then, equal to, or
** greater than B, respectively. Then the true false results is found by
** consulting sqlite3aLTb[opcode], sqlite3aEQb[opcode], or
** sqlite3aGTb[opcode] depending on whether the result of compare(A,B)
** is negative, zero, or positive, where opcode is the specific opcode.
** The only works because the comparison opcodes are consecutive and in
** this order: NE EQ GT LE LT GE. Various assert()s throughout the code
** ensure that is the case.
**
** These elements must be appended to another array. Otherwise the
** index (here shown as [256-OP_Ne]) would be out-of-bounds and thus
** be undefined behavior. That's goofy, but the C-standards people thought
** it was a good idea, so here we are.
*/
/* NE EQ GT LE LT GE */
1, 0, 0, 1, 1, 0, /* aLTb[]: Use when compare(A,B) less than zero */
0, 1, 0, 1, 0, 1, /* aEQb[]: Use when compare(A,B) equals zero */
1, 0, 1, 0, 0, 1 /* aGTb[]: Use when compare(A,B) greater than zero*/
};
const unsigned char *sqlite3aLTb = &sqlite3UpperToLower[256-OP_Ne];
const unsigned char *sqlite3aEQb = &sqlite3UpperToLower[256+6-OP_Ne];
const unsigned char *sqlite3aGTb = &sqlite3UpperToLower[256+12-OP_Ne];
/*
** The following 256 byte lookup table is used to support SQLites built-in