171c944345
variant. Update the implementation to implement its own sorting algorithm, so that the extension no longer depends on qsort(). FossilOrigin-Name: 6e31b1bab1f014933c671a12a5930c1e88d611cfe68d389e9ce888bd8842addd
271 lines
7.9 KiB
C
271 lines
7.9 KiB
C
/*
|
|
** 2013-05-28
|
|
**
|
|
** The author disclaims copyright to this source code. In place of
|
|
** a legal notice, here is a blessing:
|
|
**
|
|
** May you do good and not evil.
|
|
** May you find forgiveness for yourself and forgive others.
|
|
** May you share freely, never taking more than you give.
|
|
**
|
|
******************************************************************************
|
|
**
|
|
** This file contains code to implement the percentile(Y,P) SQL function
|
|
** as described below:
|
|
**
|
|
** (1) The percentile(Y,P) function is an aggregate function taking
|
|
** exactly two arguments.
|
|
**
|
|
** (2) If the P argument to percentile(Y,P) is not the same for every
|
|
** row in the aggregate then an error is thrown. The word "same"
|
|
** in the previous sentence means that the value differ by less
|
|
** than 0.001.
|
|
**
|
|
** (3) If the P argument to percentile(Y,P) evaluates to anything other
|
|
** than a number in the range of 0.0 to 100.0 inclusive then an
|
|
** error is thrown.
|
|
**
|
|
** (4) If any Y argument to percentile(Y,P) evaluates to a value that
|
|
** is not NULL and is not numeric then an error is thrown.
|
|
**
|
|
** (5) If any Y argument to percentile(Y,P) evaluates to plus or minus
|
|
** infinity then an error is thrown. (SQLite always interprets NaN
|
|
** values as NULL.)
|
|
**
|
|
** (6) Both Y and P in percentile(Y,P) can be arbitrary expressions,
|
|
** including CASE WHEN expressions.
|
|
**
|
|
** (7) The percentile(Y,P) aggregate is able to handle inputs of at least
|
|
** one million (1,000,000) rows.
|
|
**
|
|
** (8) If there are no non-NULL values for Y, then percentile(Y,P)
|
|
** returns NULL.
|
|
**
|
|
** (9) If there is exactly one non-NULL value for Y, the percentile(Y,P)
|
|
** returns the one Y value.
|
|
**
|
|
** (10) If there N non-NULL values of Y where N is two or more and
|
|
** the Y values are ordered from least to greatest and a graph is
|
|
** drawn from 0 to N-1 such that the height of the graph at J is
|
|
** the J-th Y value and such that straight lines are drawn between
|
|
** adjacent Y values, then the percentile(Y,P) function returns
|
|
** the height of the graph at P*(N-1)/100.
|
|
**
|
|
** (11) The percentile(Y,P) function always returns either a floating
|
|
** point number or NULL.
|
|
**
|
|
** (12) The percentile(Y,P) is implemented as a single C99 source-code
|
|
** file that compiles into a shared-library or DLL that can be loaded
|
|
** into SQLite using the sqlite3_load_extension() interface.
|
|
**
|
|
** (13) A separate median(Y) function is the equivalent percentile(Y,50).
|
|
*/
|
|
#include "sqlite3ext.h"
|
|
SQLITE_EXTENSION_INIT1
|
|
#include <assert.h>
|
|
#include <string.h>
|
|
#include <stdlib.h>
|
|
|
|
/* The following object is the session context for a single percentile()
|
|
** function. We have to remember all input Y values until the very end.
|
|
** Those values are accumulated in the Percentile.a[] array.
|
|
*/
|
|
typedef struct Percentile Percentile;
|
|
struct Percentile {
|
|
unsigned nAlloc; /* Number of slots allocated for a[] */
|
|
unsigned nUsed; /* Number of slots actually used in a[] */
|
|
double rPct; /* 1.0 more than the value for P */
|
|
double *a; /* Array of Y values */
|
|
};
|
|
|
|
/*
|
|
** Return TRUE if the input floating-point number is an infinity.
|
|
*/
|
|
static int isInfinity(double r){
|
|
sqlite3_uint64 u;
|
|
assert( sizeof(u)==sizeof(r) );
|
|
memcpy(&u, &r, sizeof(u));
|
|
return ((u>>52)&0x7ff)==0x7ff;
|
|
}
|
|
|
|
/*
|
|
** Return TRUE if two doubles differ by 0.001 or less
|
|
*/
|
|
static int sameValue(double a, double b){
|
|
a -= b;
|
|
return a>=-0.001 && a<=0.001;
|
|
}
|
|
|
|
/*
|
|
** The "step" function for percentile(Y,P) is called once for each
|
|
** input row.
|
|
*/
|
|
static void percentStep(sqlite3_context *pCtx, int argc, sqlite3_value **argv){
|
|
Percentile *p;
|
|
double rPct;
|
|
int eType;
|
|
double y;
|
|
assert( argc==2 || argc==1 );
|
|
|
|
if( argc==1 ){
|
|
/* Requirement 13: median(Y) is the same as percentile(Y,50). */
|
|
rPct = 50.0;
|
|
}else{
|
|
/* Requirement 3: P must be a number between 0 and 100 */
|
|
eType = sqlite3_value_numeric_type(argv[1]);
|
|
rPct = sqlite3_value_double(argv[1]);
|
|
if( (eType!=SQLITE_INTEGER && eType!=SQLITE_FLOAT)
|
|
|| rPct<0.0 || rPct>100.0 ){
|
|
sqlite3_result_error(pCtx, "2nd argument to percentile() is not "
|
|
"a number between 0.0 and 100.0", -1);
|
|
return;
|
|
}
|
|
}
|
|
|
|
/* Allocate the session context. */
|
|
p = (Percentile*)sqlite3_aggregate_context(pCtx, sizeof(*p));
|
|
if( p==0 ) return;
|
|
|
|
/* Remember the P value. Throw an error if the P value is different
|
|
** from any prior row, per Requirement (2). */
|
|
if( p->rPct==0.0 ){
|
|
p->rPct = rPct+1.0;
|
|
}else if( !sameValue(p->rPct,rPct+1.0) ){
|
|
sqlite3_result_error(pCtx, "2nd argument to percentile() is not the "
|
|
"same for all input rows", -1);
|
|
return;
|
|
}
|
|
|
|
/* Ignore rows for which Y is NULL */
|
|
eType = sqlite3_value_type(argv[0]);
|
|
if( eType==SQLITE_NULL ) return;
|
|
|
|
/* If not NULL, then Y must be numeric. Otherwise throw an error.
|
|
** Requirement 4 */
|
|
if( eType!=SQLITE_INTEGER && eType!=SQLITE_FLOAT ){
|
|
sqlite3_result_error(pCtx, "1st argument to percentile() is not "
|
|
"numeric", -1);
|
|
return;
|
|
}
|
|
|
|
/* Throw an error if the Y value is infinity or NaN */
|
|
y = sqlite3_value_double(argv[0]);
|
|
if( isInfinity(y) ){
|
|
sqlite3_result_error(pCtx, "Inf input to percentile()", -1);
|
|
return;
|
|
}
|
|
|
|
/* Allocate and store the Y */
|
|
if( p->nUsed>=p->nAlloc ){
|
|
unsigned n = p->nAlloc*2 + 250;
|
|
double *a = sqlite3_realloc64(p->a, sizeof(double)*n);
|
|
if( a==0 ){
|
|
sqlite3_free(p->a);
|
|
memset(p, 0, sizeof(*p));
|
|
sqlite3_result_error_nomem(pCtx);
|
|
return;
|
|
}
|
|
p->nAlloc = n;
|
|
p->a = a;
|
|
}
|
|
p->a[p->nUsed++] = y;
|
|
}
|
|
|
|
/*
|
|
** Sort an array of doubles.
|
|
*/
|
|
static void sortDoubles(double *a, int n){
|
|
int iLt; /* Entries with index less than iLt are less than rPivot */
|
|
int iGt; /* Entries with index iGt or more are greater than rPivot */
|
|
int i; /* Loop counter */
|
|
double rPivot; /* The pivot value */
|
|
double rTmp; /* Temporary used to swap two values */
|
|
|
|
if( n<2 ) return;
|
|
if( n>5 ){
|
|
rPivot = (a[0] + a[n/2] + a[n-1])/3.0;
|
|
}else{
|
|
rPivot = a[n/2];
|
|
}
|
|
iLt = i = 0;
|
|
iGt = n;
|
|
while( i<iGt ){
|
|
if( a[i]<rPivot ){
|
|
if( i>iLt ){
|
|
rTmp = a[i];
|
|
a[i] = a[iLt];
|
|
a[iLt] = rTmp;
|
|
}
|
|
iLt++;
|
|
i++;
|
|
}else if( a[i]>rPivot ){
|
|
do{
|
|
iGt--;
|
|
}while( iGt>i && a[iGt]>rPivot );
|
|
rTmp = a[i];
|
|
a[i] = a[iGt];
|
|
a[iGt] = rTmp;
|
|
}else{
|
|
i++;
|
|
}
|
|
}
|
|
if( iLt>=2 ) sortDoubles(a, iLt);
|
|
if( n-iGt>=2 ) sortDoubles(a+iGt, n-iGt);
|
|
|
|
/* Uncomment for testing */
|
|
#if 0
|
|
for(i=0; i<n-1; i++){
|
|
assert( a[i]<=a[i+1] );
|
|
}
|
|
#endif
|
|
}
|
|
|
|
/*
|
|
** Called to compute the final output of percentile() and to clean
|
|
** up all allocated memory.
|
|
*/
|
|
static void percentFinal(sqlite3_context *pCtx){
|
|
Percentile *p;
|
|
unsigned i1, i2;
|
|
double v1, v2;
|
|
double ix, vx;
|
|
p = (Percentile*)sqlite3_aggregate_context(pCtx, 0);
|
|
if( p==0 ) return;
|
|
if( p->a==0 ) return;
|
|
if( p->nUsed ){
|
|
sortDoubles(p->a, p->nUsed);
|
|
ix = (p->rPct-1.0)*(p->nUsed-1)*0.01;
|
|
i1 = (unsigned)ix;
|
|
i2 = ix==(double)i1 || i1==p->nUsed-1 ? i1 : i1+1;
|
|
v1 = p->a[i1];
|
|
v2 = p->a[i2];
|
|
vx = v1 + (v2-v1)*(ix-i1);
|
|
sqlite3_result_double(pCtx, vx);
|
|
}
|
|
sqlite3_free(p->a);
|
|
memset(p, 0, sizeof(*p));
|
|
}
|
|
|
|
|
|
#ifdef _WIN32
|
|
__declspec(dllexport)
|
|
#endif
|
|
int sqlite3_percentile_init(
|
|
sqlite3 *db,
|
|
char **pzErrMsg,
|
|
const sqlite3_api_routines *pApi
|
|
){
|
|
int rc = SQLITE_OK;
|
|
SQLITE_EXTENSION_INIT2(pApi);
|
|
(void)pzErrMsg; /* Unused parameter */
|
|
rc = sqlite3_create_function(db, "percentile", 2,
|
|
SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
|
|
0, percentStep, percentFinal);
|
|
if( rc==SQLITE_OK ){
|
|
rc = sqlite3_create_function(db, "median", 1,
|
|
SQLITE_UTF8|SQLITE_INNOCUOUS, 0,
|
|
0, percentStep, percentFinal);
|
|
}
|
|
return rc;
|
|
}
|