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Add scalar function "prefix_length()" to ext/misc/prefixes.c.

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FossilOrigin-Name: 0bf1550507d9d3c8a41f8a50db3a59bf808f0a4e24637dc0905d35579305eca7
This commit is contained in:
dan
2019-01-14 20:44:00 +00:00
parent 9274ad898f
commit 9c039d9f2e
8 changed files with 157 additions and 11 deletions
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ext/misc/prefixes.c
+52
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@@ -249,6 +249,53 @@ static sqlite3_module prefixesModule = {
/* xShadowName */ 0
};
/*
** This is a copy of the SQLITE_SKIP_UTF8(zIn) macro in sqliteInt.h.
**
** Assuming zIn points to the first byte of a UTF-8 character,
** advance zIn to point to the first byte of the next UTF-8 character.
*/
#define PREFIX_SKIP_UTF8(zIn) { \
if( (*(zIn++))>=0xc0 ){ \
while( (*zIn & 0xc0)==0x80 ){ zIn++; } \
} \
}
/*
** Implementation of function prefix_length(). This function accepts two
** strings as arguments and returns the length in characters (not bytes),
** of the longest prefix shared by the two strings. For example:
**
** prefix_length('abcdxxx', 'abcyy') == 3
** prefix_length('abcdxxx', 'bcyyy') == 0
** prefix_length('abcdxxx', 'ab') == 2
** prefix_length('ab', 'abcd') == 2
**
** This function assumes the input is well-formed utf-8. If it is not,
** it is possible for this function to return -1.
*/
static void prefixLengthFunc(
sqlite3_context *ctx,
int nVal,
sqlite3_value **apVal
){
int nByte; /* Number of bytes to compare */
int nRet = 0; /* Return value */
const unsigned char *zL = sqlite3_value_text(apVal[0]);
const unsigned char *zR = sqlite3_value_text(apVal[1]);
int nL = sqlite3_value_bytes(apVal[0]);
int nR = sqlite3_value_bytes(apVal[1]);
int i;
nByte = (nL > nR ? nL : nR);
for(i=0; i<nByte; i++){
if( zL[i]!=zR[i] ) break;
if( (zL[i] & 0xC0)!=0x80 ) nRet++;
}
if( (zL[i] & 0xC0)==0x80 ) nRet--;
sqlite3_result_int(ctx, nRet);
}
#ifdef _WIN32
__declspec(dllexport)
@@ -261,5 +308,10 @@ int sqlite3_prefixes_init(
int rc = SQLITE_OK;
SQLITE_EXTENSION_INIT2(pApi);
rc = sqlite3_create_module(db, "prefixes", &prefixesModule, 0);
if( rc==SQLITE_OK ){
rc = sqlite3_create_function(
db, "prefix_length", 2, SQLITE_UTF8, 0, prefixLengthFunc, 0, 0
);
}
return rc;
}