Improvements to rounding behavior in the round() and printf() functions.

FossilOrigin-Name: 641b2d210541b4d5a1a9e57d7dcf5ce5dfd7ff4d2dc6277ba0582869f48fc946

manifest

@@ -1,5 +1,5 @@
-C Fix\san\sfts5\ssegfault\sthat\scould\soccur\safter\sparsing\sa\scorrupt\sstructure\srecord.
-D 2019-05-24T11:55:01.124
+C Improvements\sto\srounding\sbehavior\sin\sthe\sround()\sand\sprintf()\sfunctions.
+D 2019-05-24T22:58:16.438
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -518,7 +518,7 @@ F src/pcache1.c be64b2f3908a7f97c56c963676eb12f0d6254c95b28cdc1d73a186eff213219d
 F src/pragma.c 925bcac0afd98a0d4255c7524b93239ab4d83893d96f7f8fdccd78d4929a39bb
 F src/pragma.h 4a9fabff14db4487a734dfeeb4be984ce662bfdccfae16145b9c732327735e13
 F src/prepare.c 78027c6231fbb19ca186a5f5f0c0a1375d9c2cec0655273f9bd90d9ff74a34b3
-F src/printf.c 67f79227273a9009d86a017619717c3f554f50b371294526da59faa6014ed2cd
+F src/printf.c 23a0fd3c81637d3d05340919d8a65963091e5f6597db1d275cdc9742dd970165
 F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
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 F src/rowset.c d977b011993aaea002cab3e0bb2ce50cf346000dff94e944d547b989f4b1fe93
@@ -1244,6 +1244,7 @@ F test/resolver01.test f4022acafda7f4d40eca94dbf16bc5fc4ac30ceb
 F test/rollback.test 06680159bc6746d0f26276e339e3ae2f951c64812468308838e0a3362d911eaa
 F test/rollback2.test bc868d57899dc6972e2b4483faae0e03365a0556941474eec487ae21d8d38bb6
 F test/rollbackfault.test 0e646aeab8840c399cfbfa43daab46fd609cf04a
+F test/round1.test b0b29d360acbbda7b0e7d79c75c0575808a98a7b151ae863a9a8a6a0dd7ac868
 F test/rowallock.test 3f88ec6819489d0b2341c7a7528ae17c053ab7cc
 F test/rowhash.test 0bc1d31415e4575d10cacf31e1a66b5cc0f8be81
 F test/rowid.test bfbd7b97d9267660be3c8f28507c4ed7f205196b8877c0db42df347c2e8845e3
@@ -1828,7 +1829,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
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-R f567420def97dd0b23423062e506d036
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-Z fca2e115ce615d21967ebafbe5353094
+P 600daa9c27206628bf74892376ded35dac11fe0a34894fcd975ad5041a0a0fda
+R 344188f99ea3b54a44aefc5d0b69d101
+U drh
+Z cd3c36b6c431f378c015834e2bb5423e

manifest.uuid

@@ -1 +1 @@
-600daa9c27206628bf74892376ded35dac11fe0a34894fcd975ad5041a0a0fda
+641b2d210541b4d5a1a9e57d7dcf5ce5dfd7ff4d2dc6277ba0582869f48fc946

src/printf.c

@@ -99,6 +99,12 @@ static const et_info fmtinfo[] = {
   {  'r', 10, 1, etORDINAL,    0,  0 },
 };
 
+/* Floating point constants used for rounding */
+static const double arRound[] = {
+  5.0e-01, 5.0e-02, 5.0e-03, 5.0e-04, 5.0e-05,
+  5.0e-06, 5.0e-07, 5.0e-08, 5.0e-09, 5.0e-10,
+};
+
 /*
 ** If SQLITE_OMIT_FLOATING_POINT is defined, then none of the floating point
 ** conversions will work.
@@ -517,8 +523,13 @@ void sqlite3_str_vappendf(
         }
         if( xtype==etGENERIC && precision>0 ) precision--;
         testcase( precision>0xfff );
-        for(idx=precision&0xfff, rounder=0.5; idx>0; idx--, rounder*=0.1){}
-        if( xtype==etFLOAT ) realvalue += rounder;
+        idx = precision & 0xfff;
+        rounder = arRound[idx%10];
+        while( idx>=10 ){ rounder *= 1.0e-10; idx -= 10; }
+        if( xtype==etFLOAT ){
+          if( precision<17) rounder += realvalue*2.0e-16;
+          realvalue += rounder;
+        }
         /* Normalize realvalue to within 10.0 > realvalue >= 1.0 */
         exp = 0;
         if( sqlite3IsNaN((double)realvalue) ){

test/round1.test

@@ -0,0 +1,41 @@
+# 2019-05-24
+#
+# 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.
+#
+#***********************************************************************
+# Test cases for rounding behavior of floating point values.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix round1
+
+expr srand(0)
+unset -nocomplain iTest
+for {set iTest 1} {$iTest<=10000} {incr iTest} {
+   set x1 [expr int(rand()*100000)]
+   set x2 [expr int(rand()*100000)+1000*int(rand()*10000)]
+   set n [expr int(rand()*8)+1]
+   set x3 [string range [format %09d $x2] [expr {9-$n}] end]
+   set r $x1.$x3
+   set ans [string trimright $r 0]
+   if {[string match *. $ans]} {set ans ${ans}0}
+   do_test $iTest/$n/${r}4=>$ans {
+     set x [db one "SELECT round(${r}4,$n)"]
+   } $ans
+   set x4 [string range [format %09d [expr {$x2+1}]] [expr {9-$n}] end]
+   if {[string trim $x3 9]==""} {incr x1}
+   set r2 $x1.$x4
+   set ans [string trimright $r2 0]
+   if {[string match *. $ans]} {set ans ${ans}0}
+   do_test $iTest/$n/${r}5=>$ans {
+     set x [db one "SELECT round(${r}5,$n)"]
+   } $ans
+}
+
+finish_test