From d3a149efcab431c1cfe4a828a1855963dbf1a6ef Mon Sep 17 00:00:00 2001
From: drh <drh@noemail.net>
Date: Sun, 24 Feb 2002 17:12:53 +0000
Subject: [PATCH] Added a "stddev()" aggregate function for testing the new
 user aggregate function interface. (CVS 393)

FossilOrigin-Name: 2198109712ccf988f93db5740a4f248e80fb9f5d
---
 manifest      | 12 ++++++------
 manifest.uuid |  2 +-
 src/func.c    | 47 ++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/manifest b/manifest
index 3e7fea43e5..b01eac774f 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Code\sfor\suser-defined\saggregates\sadded.\s\sLegacy\stests\sall\spass\sbut\sthere\nhas\sbeen\sno\stesting\sof\sthe\snew\suser-defined\saggregate\scode.\s(CVS\s392)
-D 2002-02-24T03:25:15
+C Added\sa\s"stddev()"\saggregate\sfunction\sfor\stesting\sthe\snew\suser\saggregate\nfunction\sinterface.\s(CVS\s393)
+D 2002-02-24T17:12:54
 F Makefile.in 50f1b3351df109b5774771350d8c1b8d3640130d
 F Makefile.template 89e373b2dad0321df00400fa968dc14b61a03296
 F README a4c0ba11354ef6ba0776b400d057c59da47a4cc0
@@ -24,7 +24,7 @@ F src/btree.h 8abeabfe6e0b1a990b64fa457592a6482f6674f3
 F src/build.c 1da051784be0155ae579d47890db74f0186f9b9f
 F src/delete.c 950d8f9097361419f1963875f9943344b469cf02
 F src/expr.c 5ed59aed47431a540263da2ca79c37a97c23e8fd
-F src/func.c f06739ac3266fe237a8079415c75b4fe27f9b604
+F src/func.c b7c1f4dd183dbca7996641017eb13bd7f820a263
 F src/hash.c cc259475e358baaf299b00a2c7370f2b03dda892
 F src/hash.h dca065dda89d4575f3176e75e9a3dc0f4b4fb8b9
 F src/insert.c 164d2d5e943268a8ff0594e1947599e04df0ce11
@@ -126,7 +126,7 @@ F www/speed.tcl 83457b2bf6bb430900bd48ca3dd98264d9a916a5
 F www/sqlite.tcl 8b5884354cb615049aed83039f8dfe1552a44279
 F www/tclsqlite.tcl 829b393d1ab187fd7a5e978631b3429318885c49
 F www/vdbe.tcl 2013852c27a02a091d39a766bc87cff329f21218
-P 530b0f4f2def89e200b7b0724a5967bf981bd91d
-R b1dfb8bf18a05ccd329e7446e18d18c8
+P 1e037eb303d8508cb2ea3418e71b03315d895fbd
+R 21d5c48b8dddd8d019c6a58015885a64
 U drh
-Z 0bcdda8b20886809bb64b19128bb3b89
+Z d7e9ee595615113d0da5c9ca524c595c
diff --git a/manifest.uuid b/manifest.uuid
index caeaedcb00..b1cfa4d76c 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1e037eb303d8508cb2ea3418e71b03315d895fbd
\ No newline at end of file
+2198109712ccf988f93db5740a4f248e80fb9f5d
\ No newline at end of file
diff --git a/src/func.c b/src/func.c
index a726c69bc3..ab45b1fea9 100644
--- a/src/func.c
+++ b/src/func.c
@@ -16,9 +16,11 @@
 ** sqliteRegisterBuildinFunctions() found at the bottom of the file.
 ** All other code has file scope.
 **
-** $Id: func.c,v 1.1 2002/02/24 01:55:17 drh Exp $
+** $Id: func.c,v 1.2 2002/02/24 17:12:54 drh Exp $
 */
 #include <ctype.h>
+#include <math.h>
+#include <stdlib.h>
 #include "sqlite.h"
 
 /*
@@ -45,6 +47,48 @@ static void lowerFunc(void *context, int argc, const char **argv){
   }
 }
 
+/*
+** An instance of the following structure holds the context of a
+** standard deviation computation.
+*/
+typedef struct StdDevCtx StdDevCtx;
+struct StdDevCtx {
+  double sum;     /* Sum of terms */
+  double sum2;    /* Sum of the squares of terms */
+  int n;          /* Number of terms seen so far */
+};
+
+/*
+** Routines used to compute the standard deviation as an aggregate.
+*/
+static void *stdDevStep(void *stddev, int argc, char **argv){
+  StdDevCtx *p;
+  double x;
+  if( argc<1 ) return 0;
+  if( stddev==0 ){
+    p = malloc( sizeof(*p) );
+    p->n = 0;
+    p->sum = 0.0;
+    p->sum2 = 0.0;
+  }else{
+    p = (StdDevCtx*)stddev;
+  }
+  x = atof(argv[0]);
+  p->sum += x;
+  p->sum2 += x*x;
+  p->n++;
+  return p;
+}
+static void stdDevFinalize(void *stddev, void *context){
+  StdDevCtx *p = (StdDevCtx*)stddev;
+  if( context && p && p->n>1 ){
+    double rN = p->n;
+    sqlite_set_result_double(context, 
+       sqrt((p->sum2 - p->sum*p->sum/rN)/(rN-1.0)));
+  }
+  if( stddev ) free(stddev);
+}
+
 /*
 ** This file registered all of the above C functions as SQL
 ** functions.
@@ -52,4 +96,5 @@ static void lowerFunc(void *context, int argc, const char **argv){
 void sqliteRegisterBuildinFunctions(sqlite *db){
   sqlite_create_function(db, "upper", 1, upperFunc);
   sqlite_create_function(db, "lower", 1, lowerFunc);
+  sqlite_create_aggregate(db, "stddev", 1, stdDevStep, stdDevFinalize);
 }