Use exp format and more precision output for ZSCAN.

Ref: issue #2175

src/db.c

@@ -381,7 +381,7 @@ void scanCallback(void *privdata, const dictEntry *de) {
     } else if (o->type == REDIS_ZSET) {
         key = dictGetKey(de);
         incrRefCount(key);
-        val = createStringObjectFromLongDouble(*(double*)dictGetVal(de));
+        val = createStringObjectFromLongDouble(*(double*)dictGetVal(de),0);
     } else {
         redisPanic("Type not handled in SCAN callback.");
     }

src/object.c

@@ -109,9 +109,11 @@ robj *createStringObjectFromLongLong(long long value) {
     return o;
 }
 
-/* Note: this function is defined into object.c since here it is where it
+/* Create a string object from a long double. If humanfriendly is non-zero
- * belongs but it is actually designed to be used just for INCRBYFLOAT */
+ * it does not use exponential format and trims trailing zeroes at the end,
-robj *createStringObjectFromLongDouble(long double value) {
+ * however this result in loss of precision. Otherwise exp format is used
+ * and the output of snprintf() is not modified. */
+robj *createStringObjectFromLongDouble(long double value, int humanfriendly) {
     char buf[256];
     int len;
 
@@ -120,6 +122,7 @@ robj *createStringObjectFromLongDouble(long double value) {
      * that is "non surprising" for the user (that is, most small decimal
      * numbers will be represented in a way that when converted back into
      * a string are exactly the same as what the user typed.) */
+    if (humanfriendly) {
         len = snprintf(buf,sizeof(buf),"%.17Lf", value);
         /* Now remove trailing zeroes after the '.' */
         if (strchr(buf,'.') != NULL) {
@@ -130,6 +133,9 @@ robj *createStringObjectFromLongDouble(long double value) {
             }
             if (*p == '.') len--;
         }
+    } else {
+        len = snprintf(buf,sizeof(buf),"%.17Lg", value);
+    }
     return createStringObject(buf,len);
 }
 

src/redis.h

@@ -1116,7 +1116,7 @@ robj *tryObjectEncoding(robj *o);
 robj *getDecodedObject(robj *o);
 size_t stringObjectLen(robj *o);
 robj *createStringObjectFromLongLong(long long value);
-robj *createStringObjectFromLongDouble(long double value);
+robj *createStringObjectFromLongDouble(long double value, int humanfriendly);
 robj *createListObject(void);
 robj *createZiplistObject(void);
 robj *createSetObject(void);

src/t_hash.c

@@ -565,7 +565,7 @@ void hincrbyfloatCommand(redisClient *c) {
     }
 
     value += incr;
-    new = createStringObjectFromLongDouble(value);
+    new = createStringObjectFromLongDouble(value,1);
     hashTypeTryObjectEncoding(o,&c->argv[2],NULL);
     hashTypeSet(o,c->argv[2],new);
     addReplyBulk(c,new);

src/t_string.c

@@ -397,7 +397,7 @@ void incrbyfloatCommand(redisClient *c) {
         addReplyError(c,"increment would produce NaN or Infinity");
         return;
     }
-    new = createStringObjectFromLongDouble(value);
+    new = createStringObjectFromLongDouble(value,1);
     if (o)
         dbOverwrite(c->db,c->argv[1],new);
     else