Increased precision of floating-point to decimal conversions when the

floating point value has no fractional part.
[forum:/forumpost/d1387c3979c7f557|Forum post d1387c3979c7f557]

FossilOrigin-Name: 18de3a8e6b431a075143631eafdcf0e1b1a21868b417394c365d46d2feca10b5

manifest

@@ -1,5 +1,5 @@
-C Fix\sharmless\scompiler\swarnings\sand\sa\scode\sindentation\serror.
+C Increased\sprecision\sof\sfloating-point\sto\sdecimal\sconversions\swhen\sthe\nfloating\spoint\svalue\shas\sno\sfractional\spart.\n[forum:/forumpost/d1387c3979c7f557|Forum\spost\sd1387c3979c7f557]
-D 2023-02-23T14:43:15.500
+D 2023-02-23T21:18:47.560
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -617,7 +617,7 @@ F src/pcache1.c dee95e3cd2b61e6512dc814c5ab76d5eb36f0bfc9441dbb4260fccc0d12bbddc
 F src/pragma.c 82d5090a35eac75876d3b41f48d06b2370553c9576bf2942233c462e03eb94c9
 F src/pragma.h e690a356c18e98414d2e870ea791c1be1545a714ba623719deb63f7f226d8bb7
 F src/prepare.c ce87a08cfddd45a147150db34190b1986f2d4a0e0828858cb6bd908c78fb02e3
-F src/printf.c ff4b05e38bf928ff1b80d3dda4f977b10fe39ecbfe69c018224c7e5594fb2455
+F src/printf.c d7b8c87d3525ee3eea3c4d291023540c88788e47a65c5b1dcff1b432ec9dbda5
 F src/random.c 606b00941a1d7dd09c381d3279a058d771f406c5213c9932bbd93d5587be4b9c
 F src/resolve.c d62c5665279cc7485f9d45b5e20911cc7b19c203f268321a90d05d74f4725750
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
@@ -1381,7 +1381,7 @@ F test/pragma4.test ca5e4dfc46adfe490f75d73734f70349d95a199e6510973899e502eef2c8
 F test/pragma5.test 7b33fc43e2e41abf17f35fb73f71b49671a380ea92a6c94b6ce530a25f8d9102
 F test/pragmafault.test 275edaf3161771d37de60e5c2b412627ac94cef11739236bec12ed1258b240f8
 F test/prefixes.test b524a1c44bffec225b9aec98bd728480352aa8532ac4c15771fb85e8beef65d9
-F test/printf.test 390d0d7fcffc3c4ea3c1bb4cbb267444e32b33b048ae21895f23a291844fe1da
+F test/printf.test 22449e13983e9d94fe9a671db68a086c4c55dea51daad825ef7ebb3d192ee997
 F test/printf2.test 3f55c1871a5a65507416076f6eb97e738d5210aeda7595a74ee895f2224cce60
 F test/progress.test ebab27f670bd0d4eb9d20d49cef96e68141d92fb
 F test/ptrchng.test ef1aa72d6cf35a2bbd0869a649b744e9d84977fc
@@ -2046,8 +2046,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 7ee22f95e7a7d8650f961f20e304e56c7813e624f05655d7392ca9347748270f
+P de6c5c6bb49a0beca793cdc0462da2c17bb05f3292e08dd815be29b45b59a8fb
-R 6f3dc9114a2c05702b3aef7d84d0887b
+R 4769ae3a046ae725cd776ab02bbf2890
 U drh
-Z ad82adef5ba3f74b5f1d1691fda9e306
+Z bc3a2ae65a6e7b1f83be3e57f2f8ed26
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-de6c5c6bb49a0beca793cdc0462da2c17bb05f3292e08dd815be29b45b59a8fb
+18de3a8e6b431a075143631eafdcf0e1b1a21868b417394c365d46d2feca10b5

src/printf.c

@@ -142,6 +142,20 @@ static char et_getdigit(LONGDOUBLE_TYPE *val, int *cnt){
 }
 #endif /* SQLITE_OMIT_FLOATING_POINT */
 
+#ifndef SQLITE_OMIT_FLOATING_POINT
+/*
+** "*val" is a u64.  *msd is a divisor used to extract the
+** most significant digit of *val.  Extract that most significant
+** digit and return it.
+*/
+static char et_getdigit_int(u64 *val, u64 *msd){
+  u64 x = (*val)/(*msd);
+  *val -= x*(*msd);
+  if( *msd>=10 ) *msd /= 10;
+  return '0' + (char)(x & 15);
+}
+#endif /* SQLITE_OMIT_FLOATING_POINT */
+
 /*
 ** Set the StrAccum object to an error mode.
 */
@@ -234,6 +248,8 @@ void sqlite3_str_vappendf(
   char prefix;               /* Prefix character.  "+" or "-" or " " or '\0'. */
   sqlite_uint64 longvalue;   /* Value for integer types */
   LONGDOUBLE_TYPE realvalue; /* Value for real types */
+  sqlite_uint64 msd;         /* Divisor to get most-significant-digit
+                             ** of longvalue */
   const et_info *infop;      /* Pointer to the appropriate info structure */
   char *zOut;                /* Rendering buffer */
   int nOut;                  /* Size of the rendering buffer */
@@ -540,9 +556,27 @@ void sqlite3_str_vappendf(
         }else{
           prefix = flag_prefix;
         }
+        exp = 0;
         if( xtype==etGENERIC && precision>0 ) precision--;
         testcase( precision>0xfff );
+        if( realvalue<1.0e+16
+         && realvalue==(LONGDOUBLE_TYPE)(longvalue = (u64)realvalue)
+        ){
+          /* Number is a pure integer that can be represented as u64 */
+          for(msd=1; msd*10<=longvalue; msd *= 10, exp++){}
+          if( exp>precision && xtype!=etFLOAT ){
+            u64 rnd = msd/2;
+            int kk = precision;
+            while( kk-- > 0 && rnd ){  rnd /= 10; }
+            longvalue += rnd;
+          }
+        }else{
+          msd = 0;
+          longvalue = 0;  /* To prevent a compiler warning */
           idx = precision & 0xfff;
+          if( idx>20 ){
+            rounder = 0.0;
+          }else{
             rounder = arRound[idx%10];
             while( idx>=10 ){ rounder *= 1.0e-10; idx -= 10; }
             if( xtype==etFLOAT ){
@@ -554,13 +588,14 @@ void sqlite3_str_vappendf(
               if( precision+(ex/3) < 15 ) rounder += realvalue*3e-16;
               realvalue += rounder;
             }
-        /* Normalize realvalue to within 10.0 > realvalue >= 1.0 */
+          }
-        exp = 0;
           if( sqlite3IsNaN((double)realvalue) ){
             bufpt = "NaN";
             length = 3;
             break;
           }
+
+          /* Normalize realvalue to within 10.0 > realvalue >= 1.0 */
           if( realvalue>0.0 ){
             LONGDOUBLE_TYPE scale = 1.0;
             while( realvalue>=1e100*scale && exp<=350){ scale*=1e100;exp+=100;}
@@ -576,16 +611,17 @@ void sqlite3_str_vappendf(
               length = 3+(prefix!=0);
               break;
             }
-        }
-        bufpt = buf;
-        /*
-        ** If the field type is etGENERIC, then convert to either etEXP
-        ** or etFLOAT, as appropriate.
-        */
             if( xtype!=etFLOAT ){
               realvalue += rounder;
               if( realvalue>=10.0 ){ realvalue *= 0.1; exp++; }
             }
+          }
+        }
+
+        /*
+        ** If the field type is etGENERIC, then convert to either etEXP
+        ** or etFLOAT, as appropriate.
+        */
         if( xtype==etGENERIC ){
           flag_rtz = !flag_alternateform;
           if( exp<-4 || exp>precision ){
@@ -602,6 +638,8 @@ void sqlite3_str_vappendf(
         }else{
           e2 = exp;
         }
+        nsd = 16 + flag_altform2*10;
+        bufpt = buf;
         {
           i64 szBufNeeded;           /* Size of a temporary buffer needed */
           szBufNeeded = MAX(e2,0)+(i64)precision+(i64)width+15;
@@ -611,7 +649,6 @@ void sqlite3_str_vappendf(
           }
         }
         zOut = bufpt;
-        nsd = 16 + flag_altform2*10;
         flag_dp = (precision>0 ?1:0) | flag_alternateform | flag_altform2;
         /* The sign in front of the number */
         if( prefix ){
@@ -620,6 +657,10 @@ void sqlite3_str_vappendf(
         /* Digits prior to the decimal point */
         if( e2<0 ){
           *(bufpt++) = '0';
+        }else if( msd>0 ){
+          for(; e2>=0; e2--){
+            *(bufpt++) = et_getdigit_int(&longvalue,&msd);
+          }
         }else{
           for(; e2>=0; e2--){
             *(bufpt++) = et_getdigit(&realvalue,&nsd);
@@ -636,9 +677,15 @@ void sqlite3_str_vappendf(
           *(bufpt++) = '0';
         }
         /* Significant digits after the decimal point */
+        if( msd>0 ){
+          while( (precision--)>0 ){
+            *(bufpt++) = et_getdigit_int(&longvalue,&msd);
+          }
+        }else{
           while( (precision--)>0 ){
             *(bufpt++) = et_getdigit(&realvalue,&nsd);
           }
+        }
         /* Remove trailing zeros and the "." if no digits follow the "." */
         if( flag_rtz && flag_dp ){
           while( bufpt[-1]=='0' ) *(--bufpt) = 0;

test/printf.test

@@ -3786,4 +3786,39 @@ do_execsql_test printf-16.1 {
   SELECT printf('%.*g',2147483647,0.01);
 } {0.01}
 
+# 2023-02-23 https://sqlite.org/forum/forumpost/d1387c3979c7f557
+# Loss of precision when doing floating-point to decimal
+# conversions on values that have no factional part.
+#
+do_execsql_test printf-17.1 {
+  SELECT format('%!.20g', 13.0);
+} 13.0
+do_execsql_test printf-17.2 {
+  SELECT format('%.3e', 199990000.0);
+} 2.000e+08
+do_execsql_test printf-17.3 {
+  SELECT format('%.3f', 199990000.0);
+} 199990000.000
+do_execsql_test printf-17.4 {
+  SELECT format('%.3g', 199990000.0);
+} 2e+08
+do_execsql_test printf-17.5 {
+  SELECT format('%.4e', 199990000.0);
+} 1.9999e+08
+do_execsql_test printf-17.6 {
+  SELECT format('%.4f', 199990000.0);
+} 199990000.0000
+do_execsql_test printf-17.7 {
+  SELECT format('%.4g', 199990000.0);
+} 2e+08
+do_execsql_test printf-17.8 {
+  SELECT format('%.5e', 199990000.0);
+} 1.99990e+08
+do_execsql_test printf-17.9 {
+  SELECT format('%.5f', 199990000.0);
+} 199990000.00000
+do_execsql_test printf-17.10 {
+  SELECT format('%.5g', 199990000.0);
+} 1.9999e+08
+
 finish_test