Performance improvement by unwinding a loop in jsonAppendString().

FossilOrigin-Name: 190ab3c08431a0ba24d76392eab251f5c1792add05e4ec780998b299208eca95

manifest

@@ -1,5 +1,5 @@
-C Fix\sharmless\scompiler\swarnings\sin\sFTS5.
-D 2023-12-28T16:25:48.632
+C Performance\simprovement\sby\sunwinding\sa\sloop\sin\sjsonAppendString().
+D 2023-12-28T19:18:08.833
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -697,7 +697,7 @@ F src/hash.h 3340ab6e1d13e725571d7cee6d3e3135f0779a7d8e76a9ce0a85971fa3953c51
 F src/hwtime.h f9c2dfb84dce7acf95ce6d289e46f5f9d3d1afd328e53da8f8e9008e3b3caae6
 F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
 F src/insert.c 3f0a94082d978bbdd33c38fefea15346c6c6bffb70bc645a71dc0f1f87dd3276
-F src/json.c 4e389cbf100c53c19fff7e6fca50efb8b1ed989350eb1ae25e2950416cc9c972
+F src/json.c a84de35816b8aebf6a97e08887cce486c0591d0b6147088fa888325f0c17f9ef
 F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
 F src/loadext.c 7432c944ff197046d67a1207790a1b13eec4548c85a9457eb0896bb3641dfb36
 F src/main.c ce714ee501122c76eb2e69b292bebe443aba611fc3b88e6786eb910285515fe4
@@ -2156,8 +2156,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 056de8d551dcbdf1d162e2db15ed418fa9c786f900cd3972ef8a1dea3f4f3aa1
-R a054d36d3399814c54294e63ea00ca79
+P 3cd5ef44e40570c357f913a9483fa1cd72e7f2827a5ed5826bff99febae213b1
+R 1e6a2dd6f87f9d0628f571e967da7d98
 U drh
-Z 9a8f01391d6842f16881c897399abbc0
+Z 7e6ac710b6732b62be341bd93538e4ea
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-3cd5ef44e40570c357f913a9483fa1cd72e7f2827a5ed5826bff99febae213b1
+190ab3c08431a0ba24d76392eab251f5c1792add05e4ec780998b299208eca95

src/json.c

@@ -627,8 +627,33 @@ static void jsonAppendString(JsonString *p, const char *zIn, u32 N){
   p->zBuf[p->nUsed++] = '"';
   while( 1 /*exit-by-break*/ ){
     k = 0;
-    while( k+1<N && jsonIsOk[z[k]] && jsonIsOk[z[k+1]] ){ k += 2; } /* <--, */
-    while( k<N && jsonIsOk[z[k]] ){ k++; }    /* <-- loop unwound for speed  */
+    /* The following while() is the 4-way unwound equivalent of
+    **
+    **     while( k<N && jsonIsOk[z[k]] ){ k++; }
+    */
+    while( 1 /* Exit by break */ ){
+      if( k+3>=N ){
+        while( k<N && jsonIsOk[z[k]] ){ k++; }
+        break;
+      }
+      if( !jsonIsOk[z[k]] ){
+        break;
+      }
+      if( !jsonIsOk[z[k+1]] ){
+        k += 1;
+        break;
+      }
+      if( !jsonIsOk[z[k+2]] ){
+        k += 2;
+        break;
+      }
+      if( !jsonIsOk[z[k+3]] ){
+        k += 3;
+        break;
+      }else{
+        k += 4;
+      }
+    }
     if( k>=N ){
       if( k>0 ){
         memcpy(&p->zBuf[p->nUsed], z, k);