Faster and smaller implementation of sqlite3AtoF() based on a suggestion

from Cezary H. Noweta.

FossilOrigin-Name: fd2e0e7a770c2ce9355068aad1024c3d2861c104fd3be304a91c55ca742155fa

diff --git a/manifest b/manifest
index f3f08454e95860b14fbd3c85afadc3cf3a2aa487..3d3fdb11e9b3d5b89852b3bb16da3c9f561ef474 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\scrashes\sthat\scould\soccur\sif\sSQL\sNULL\svalues\swere\spassed\sto\sthe\sbuilt-in\nFTS5\ssnippet\sfunction.\sEdit:\sbreaks\samalgamation\sbuilds.
-D 2017-12-26T14:32:25.807
+C Faster\sand\ssmaller\simplementation\sof\ssqlite3AtoF()\sbased\son\sa\ssuggestion\nfrom\sCezary\sH.\sNoweta.
+D 2017-12-26T14:46:20.800
 F Makefile.in ceb40bfcb30ebba8e1202b34c56ff7e13e112f9809e2381d99be32c2726058f5
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 6480671f7c129e61208d69492b3c71ce4310d49fceac83cfb17f1c081e242b69
@@ -545,7 +545,7 @@ F src/treeview.c eae35972ff44f67064de2eaf35f04afe94e7aea3271a8b3bcebb3f954880fec
 F src/trigger.c 775053eecf6b73062e243404b56f5064446254d5cce17d8704d5cdffd72a546a
 F src/update.c 961bd1265d4d1e5cd65c9a54fa5122fb7aefcb003fcf2de0c092fceb7e58972c
 F src/utf.c 810fbfebe12359f10bc2a011520a6e10879ab2a163bcb26c74768eab82ea62a5
-F src/util.c d01fa6f45bfad3b65fb2490513aa2e0676412c61b4b094340b513cf72c3704a4
+F src/util.c 7315e97a8dc2c8e19ca64196c652cf0a65d13fd0a211b2cec082062372dc6261
 F src/vacuum.c 90839322fd5f00df9617eb21b68beda9b6e2a2937576b0d65985e4aeb1c53739
 F src/vdbe.c 3393b508d9ad084ffce232a7c53e375ef5ac99b50b685c5131fcdfce97a9d534
 F src/vdbe.h d50cadf12bcf9fb99117ef392ce1ea283aa429270481426b6e8b0280c101fd97
@@ -1687,8 +1687,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P ebfea8728fec955b1d74b1d0a3de498fd1a32e8b39572a8fdab606ed87b169b4
-Q +553a3ad32498ddda920216cd44a376a439a58fbb326d2d3800528867db1ffa9d
-R 742f62796704fae3ae9dc15618c72290
-U dan
-Z ecb93df9cf8c6f4bd1c8f7a6ca97d753
+P 6a790b67a0a5c698526db16ea262b13ecdd1b6ca74e80bdccfcad88ddbdc933a
+R c3240df89b3aa2504611bdd745085460
+U drh
+Z 3dc20c6e2c72c6078d443025934f152b

diff --git a/manifest.uuid b/manifest.uuid
index 9c54144feeb65e877c19ba929a2a7e7962792efd..bdfe92339c05d6ff93d4421812fc1b860f202ab9 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6a790b67a0a5c698526db16ea262b13ecdd1b6ca74e80bdccfcad88ddbdc933a
\ No newline at end of file
+fd2e0e7a770c2ce9355068aad1024c3d2861c104fd3be304a91c55ca742155fa
\ No newline at end of file

diff --git a/src/util.c b/src/util.c
index a4dbe8fdaf30ffe4cf595214bfbcf3a272c8cace..75de4b3b307fd8be265cfe327d6e6bbc242f4bfd 100644 (file)
--- a/src/util.c
+++ b/src/util.c
@@ -320,6 +320,24 @@ int sqlite3_strnicmp(const char *zLeft, const char *zRight, int N){
   return N<0 ? 0 : UpperToLower[*a] - UpperToLower[*b];
 }
 
+/*
+** Compute 10 to the E-th power.  Examples:  E==1 results in 10.
+** E==2 results in 100.  E==50 results in 1.0e50.
+**
+** This routine only works for values of E between 1 and 341.
+*/
+static LONGDOUBLE_TYPE sqlite3Pow10(int E){
+  LONGDOUBLE_TYPE x = 10.0;
+  LONGDOUBLE_TYPE r = 1.0;
+  while(1){
+    if( E & 1 ) r *= x;
+    E >>= 1;
+    if( E==0 ) break;
+    x *= x;
+  }
+  return r; 
+}
+
 /*
 ** The string z[] is an text representation of a real number.
 ** Convert this string to a double and write it into *pResult.
@@ -475,11 +493,10 @@ do_atof_calc:
     if( e==0 ){                                         /*OPTIMIZATION-IF-TRUE*/
       result = (double)s;
     }else{
-      LONGDOUBLE_TYPE scale = 1.0;
       /* attempt to handle extremely small/large numbers better */
       if( e>307 ){                                      /*OPTIMIZATION-IF-TRUE*/
         if( e<342 ){                                    /*OPTIMIZATION-IF-TRUE*/
-          while( e%308 ) { scale *= 1.0e+1; e -= 1; }
+          LONGDOUBLE_TYPE scale = sqlite3Pow10(e-308);
           if( esign<0 ){
             result = s / scale;
             result /= 1.0e+308;
@@ -499,10 +516,7 @@ do_atof_calc:
           }
         }
       }else{
-        /* 1.0e+22 is the largest power of 10 than can be 
-        ** represented exactly. */
-        while( e%22 ) { scale *= 1.0e+1; e -= 1; }
-        while( e>0 ) { scale *= 1.0e+22; e -= 22; }
+        LONGDOUBLE_TYPE scale = sqlite3Pow10(e);
         if( esign<0 ){
           result = s / scale;
         }else{