Introduce String::append_float

This method will write out a float to a String object, keeping the
charset of the original string.

Also have Float::to_string make use of String::append_float

sql/sql_string.cc

@@ -118,6 +118,38 @@ bool Binary_string::realloc_raw(size_t alloc_length)
 }
 
 
+static uint32 write_float_str_to_buff(char *buff, int buff_len,
+                                      float num, uint decimals)
+{
+  if (decimals >= FLOATING_POINT_DECIMALS)
+    return (uint32)my_gcvt(num, MY_GCVT_ARG_FLOAT, buff_len - 1, buff, NULL);
+  else
+    return (uint32)my_fcvt(num, decimals, buff, NULL);
+}
+
+bool String::append_float(float num, uint decimals)
+{
+  uint dummy_errors;
+  size_t len;
+  DBUG_ASSERT(!std::isnan(num));
+  DBUG_ASSERT(!std::isinf(num));
+  if (realloc_with_extra_if_needed(str_length + FLOATING_POINT_BUFFER))
+    return true;
+
+  if (charset()->mbminlen > 1)
+  {
+    char buff[FLOATING_POINT_BUFFER];
+    len= write_float_str_to_buff(buff, sizeof(buff), num, decimals);
+    str_length+= copy_and_convert(Ptr + str_length, len, charset(), buff, len,
+                                  &my_charset_latin1, &dummy_errors);
+  }
+  else
+    str_length+= write_float_str_to_buff(Ptr + str_length,
+                                         FLOATING_POINT_BUFFER, num, decimals);
+  return false;
+}
+
+
 bool String::set_int(longlong num, bool unsigned_flag, CHARSET_INFO *cs)
 {
   /*

sql/sql_string.h

@@ -20,9 +20,13 @@
 
 /* This file is originally from the mysql distribution. Coded by monty */
 
+#include <my_global.h>
+#include <cmath>
+
 #include "m_ctype.h"                            /* my_charset_bin */
 #include <my_sys.h>              /* alloc_root, my_free, my_realloc */
 #include "m_string.h"                           /* TRASH */
+#include "sql_const.h"
 #include "sql_list.h"
 
 class String;
@@ -1007,6 +1011,12 @@ class String: public Charset, public Binary_string
   {
     return Binary_string::append(s);
   }
+
+  // Append a float value to the string keeping the string's charset.
+  //
+  // The float value must not be NaN or Inf, it will be represented as 0 in
+  // that case.
+  bool append_float(float num, uint decimals);
   inline bool append(char chr)
   {
     return Binary_string::append_char(chr);

sql/sql_type.cc

@@ -328,27 +328,9 @@ Type_handler_data *type_handler_data= NULL;
 
 bool Float::to_string(String *val_buffer, uint dec) const
 {
-  uint to_length= 70;
-  if (val_buffer->alloc(to_length))
-    return true;
-
-  char *to=(char*) val_buffer->ptr();
-  size_t len;
-
-  if (dec >= FLOATING_POINT_DECIMALS)
-    len= my_gcvt(m_value, MY_GCVT_ARG_FLOAT, to_length - 1, to, NULL);
-  else
-  {
-    /*
-      We are safe here because the buffer length is 70, and
-      fabs(float) < 10^39, dec < FLOATING_POINT_DECIMALS. So the resulting string
-      will be not longer than 69 chars + terminating '\0'.
-    */
-    len= my_fcvt(m_value, (int) dec, to, NULL);
-  }
-  val_buffer->length((uint) len);
   val_buffer->set_charset(&my_charset_numeric);
-  return false;
+  val_buffer->length(0);
+  return val_buffer->append_float(m_value, dec);
 }