From: drh <>
Date: Mon, 10 Jun 2024 14:31:07 +0000 (+0000)
Subject: Change the rounding behavior of float point to decimal conversions such that
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a6a765efd25a8f4190627b9b551325f9f810072c;p=thirdparty%2Fsqlite.git

Change the rounding behavior of float point to decimal conversions such that
if the next digit is 4 but the value is within one epsilon of the next digit
being 5 and if the epsilon is small compared the number of digits to be
rendered, then go ahead and round up anyhow,
even though the correct behavior would be to round down.

FossilOrigin-Name: 4a790d3b28685f08bbb722057cd6a97aea08a2b2a6098562c6373fd3b5b7206c
---

diff --git a/manifest b/manifest
index 074d16815b..8d40a46dd4 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Improved\sheader\scomment\son\sthe\ssqlite3FpDecode()\simplementation.\nFor\sthe\sfpdecode()\sSQL\sfunction\s(available\sin\sdebug\sbuilds\sonly)\slimit\nthe\svalue\sof\sthe\sthird\sparameter\s(mxRound)\sto\sbe\spositive.
-D 2024-06-10T12:43:03.794
+C Change\sthe\srounding\sbehavior\sof\sfloat\spoint\sto\sdecimal\sconversions\ssuch\sthat\nif\sthe\snext\sdigit\sis\s4\sbut\sthe\svalue\sis\swithin\sone\sepsilon\sof\sthe\snext\sdigit\nbeing\s5\sand\sif\sthe\sepsilon\sis\ssmall\scompared\sthe\snumber\sof\sdigits\sto\sbe\nrendered,\sthen\sgo\sahead\sand\sround\sup\sanyhow,\neven\sthough\sthe\scorrect\sbehavior\swould\sbe\sto\sround\sdown.
+D 2024-06-10T14:31:07.017
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -823,7 +823,7 @@ F src/trigger.c 0858f75818ed1580332db274f1032bcc5effe567cb132df5c5be8b1d800ca97f
 F src/update.c 732404a04d1737ef14bb6ec6b84f74edf28b3c102a92ae46b4855438a710efe7
 F src/upsert.c 2e60567a0e9e8520c18671b30712a88dc73534474304af94f32bb5f3ef65ac65
 F src/utf.c f23165685a67b4caf8ec08fb274cb3f319103decfb2a980b7cfd55d18dfa855e
-F src/util.c 5d1a0134cf4240648d1c6bb5cc8efaca0ea2b5d5c840985aec7e947271f04375
+F src/util.c cedda44359c51d971557614216085c31d78ee7d23cc89400061c5433855aff64
 F src/vacuum.c 604fcdaebe76f3497c855afcbf91b8fa5046b32de3045bab89cc008d68e40104
 F src/vdbe.c b05777c3ff2ed7b9dfc347e7cdee18e371aa6811cef1fe83454691b0dbe2cc9f
 F src/vdbe.h c2d78d15112c3fc5ab87f5e8e0b75d2db1c624409de2e858c3d1aafb1650bb4f
@@ -1543,6 +1543,7 @@ F test/rollback.test 06680159bc6746d0f26276e339e3ae2f951c64812468308838e0a3362d9
 F test/rollback2.test 3f3a4e20401825017df7e7671e9f31b6de5fae5620c2b9b49917f52f8c160a8f
 F test/rollbackfault.test 0e646aeab8840c399cfbfa43daab46fd609cf04a
 F test/round1.test 29c3c9039936ed024d672f003c4d35ee11c14c0acb75c5f7d6188ff16190cfd4
+F test/round2.test d2ab6f54156fe5e4a822e3b5e4de69a4b963439797c2dc516d00ce5fb22b6e17
 F test/rowallock.test 3f88ec6819489d0b2341c7a7528ae17c053ab7cc
 F test/rowhash.test 0bc1d31415e4575d10cacf31e1a66b5cc0f8be81
 F test/rowid.test d27191b5ce794c05bf61081e8b2c546a1844c1641321dcaf7fb785234256cc8e
@@ -2195,8 +2196,11 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 40de3939792e17df25598b3e60d1cebcecde2b00832acd55604f14b21398a9a7
-R 3798b5dfb33f66d6cffbf2ab99073009
+P 56af06fa12104a1fe119d7087746011183af053834eac72d0fb69f60d98054c6
+R d2547c87a8223548d3daae3e983f63e3
+T *branch * round-up
+T *sym-round-up *
+T -sym-trunk *
 U drh
-Z 6cba9a77bc527574a7f08d08f1d8739d
+Z fe023add6bc94c6c74f3cca88a0e7276
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index d58d474cbf..79ca38fb04 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-56af06fa12104a1fe119d7087746011183af053834eac72d0fb69f60d98054c6
\ No newline at end of file
+4a790d3b28685f08bbb722057cd6a97aea08a2b2a6098562c6373fd3b5b7206c
\ No newline at end of file
diff --git a/src/util.c b/src/util.c
index 0cebb474a2..fb25fa4b29 100644
--- a/src/util.c
+++ b/src/util.c
@@ -1011,6 +1011,18 @@ int sqlite3Atoi(const char *z){
   return x;
 }
 
+/*
+** Return true if the first N characters of string z[] are '9'
+*/
+static SQLITE_NOINLINE int allNines(const char *z, int N){
+  int i;
+  assert( N>0 );
+  for(i=0; i<N; i++){
+    if( z[i]!='9' ) return 0;
+  }
+  return 1;
+}
+
 /*
 ** Decode a floating-point value into an approximate decimal
 ** representation.
@@ -1027,6 +1039,21 @@ int sqlite3Atoi(const char *z){
 ** stored in p->z[] which is a often (but not always) a pointer
 ** into the middle of p->zBuf[].  There are p->n significant digits.
 ** The p->z[] array is *not* zero-terminated.
+**
+** Rounding Behavior:
+**
+**   (1)  If the next digit is 3 or less, then truncate.  Do not round.
+**
+**   (2)  If the next digit is 5 or more, then round up.
+**
+**   (3)  Round up if the next digit is a 4 followed by three or
+**        more 9 digits and all digits after the 4 up to the
+**        antipenultimate digit are 9.  Otherwise truncate.
+**
+** Rule (3) is so that things like round(0.15,1) will come out as 0.2
+** even though the stored value for 0.15 is really
+** 0.1499999999999999944488848768742172978818416595458984375 and ought
+** to round down to 0.1.
 */
 void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
   int i;
@@ -1140,8 +1167,10 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
   if( iRound>0 && (iRound<p->n || p->n>mxRound) ){
     char *z = &p->zBuf[i+1];
     if( iRound>mxRound ) iRound = mxRound;
-    p->n = iRound;
-    if( z[iRound]>='5' ){
+    if( z[iRound]>='5'
+     || (z[iRound]=='4' && p->n>iRound+5
+                        && allNines(&z[iRound+1],p->n-iRound-3))
+    ){
       int j = iRound-1;
       while( 1 /*exit-by-break*/ ){
         z[j]++;
@@ -1149,7 +1178,7 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
         z[j] = '0';
         if( j==0 ){
           p->z[i--] = '1';
-          p->n++;
+          iRound++;
           p->iDP++;
           break;
         }else{
@@ -1157,7 +1186,8 @@ void sqlite3FpDecode(FpDecode *p, double r, int iRound, int mxRound){
         }
       }
     }
-  }
+    p->n = iRound;
+ }
   p->z = &p->zBuf[i+1];
   assert( i+p->n < sizeof(p->zBuf) );
   while( ALWAYS(p->n>0) && p->z[p->n-1]=='0' ){ p->n--; }
diff --git a/test/round2.test b/test/round2.test
new file mode 100644
index 0000000000..1847516dc5
--- /dev/null
+++ b/test/round2.test
@@ -0,0 +1,43 @@
+# 2024-06-10
+#
+# 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.
+#
+#***********************************************************************
+# 
+#  https://sqlite.org/forum/forumpost/c0753dfb2d5d7f75
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix round2
+
+load_static_extension db stmtrand
+do_execsql_test 1.1 {
+  WITH RECURSIVE
+    c(n) AS (VALUES(0) UNION ALL SELECT n+1 FROM c WHERE n<100000),
+    r(a,b) AS MATERIALIZED (SELECT stmtrand()%100000, stmtrand()%100000 FROM c),
+    f(x,y,n) AS (
+       SELECT CAST(format('%d.%d5',a,b) AS real),
+              CAST(format('%d.%d6',a,b) AS real),
+               length(format('%d',b)) FROM r)
+    SELECT x, n, round(x,n), round(y,n) FROM f
+     WHERE round(x,n)<>round(y,n);
+
+} {}
+do_execsql_test 1.2 {
+  SELECT round(0.15,1);
+} 0.2
+do_execsql_test 1.3 {
+  SELECT round(0.14999999999999999,1);
+} 0.2
+do_execsql_test 1.4 {
+  SELECT round(0.1499999999999999944488848768742172978818416595458984375,1);
+} 0.2
+
+
+finish_test