Backport of WL #2934: Make/find library for doing float/double

                      to string conversions and vice versa" 
Initial import of the dtoa.c code and custom wrappers around it 
to allow its usage from the server code. 
 
Conversion of FLOAT/DOUBLE values to DECIMAL ones or strings 
and vice versa has been significantly reworked. As the new 
algoritms are more precise than the older ones, results of such 
conversions may not always match those obtained from older 
server versions. This in turn may break compatibility for some 
applications. 
 
This patch also fixes the following bugs: 
- bug #12860 "Difference in zero padding of exponent between 
Unix and Windows" 
- bug #21497 "DOUBLE truncated to unusable value" 
- bug #26788 "mysqld (debug) aborts when inserting specific 
numbers into char fields" 
- bug #24541 "Data truncated..." on decimal type columns 
without any good reason" 

1 files changed, 20 insertions, 34 deletions

diff --git a/libmysql/libmysql.c b/libmysql/libmysql.c
index 6f5fcd187b7..ec7263e2dd8 100644
--- a/libmysql/libmysql.c
+++ b/libmysql/libmysql.c
@@ -3372,12 +3372,13 @@ static void fetch_long_with_conversion(MYSQL_BIND *param, MYSQL_FIELD *field,
     param   output buffer descriptor
     field   column metadata
     value   column data
-    width   default number of significant digits used when converting
-            float/double to string
+    type    either MY_GCVT_ARG_FLOAT or MY_GCVT_ARG_DOUBLE.
+            Affects the maximum number of significant digits
+            returned by my_gcvt().
 */
 
 static void fetch_float_with_conversion(MYSQL_BIND *param, MYSQL_FIELD *field,
-                                        double value, int width)
+                                        double value, my_gcvt_arg_type type)
 {
   char *buffer= (char *)param->buffer;
   double val64 = (value < 0 ? -floor(-value) : floor(value));
@@ -3461,39 +3462,24 @@ static void fetch_float_with_conversion(MYSQL_BIND *param, MYSQL_FIELD *field,
       floating point -> string conversion nicely, honor all typecodes
       and param->offset possibly set in mysql_stmt_fetch_column
     */
-    char buff[MAX_DOUBLE_STRING_REP_LENGTH];
-    char *end;
+    char buff[FLOATING_POINT_BUFFER];
+    size_t len;
     if (field->decimals >= NOT_FIXED_DEC)
-    {
-      /*
-        DBL_DIG below is to ensure that the server and client has the same
-        precisions. This will ensure that on the same machine you get the
-        same value as a string independent of the protocol you use.
-      */
-      sprintf(buff, "%-*.*g", (int) min(sizeof(buff)-1,
-                                        param->buffer_length),
-              min(DBL_DIG, width), value);
-      end= strcend(buff, ' ');
-      *end= 0;
-    }
+      len= my_gcvt(value, type,
+                   (int) min(sizeof(buff)-1, param->buffer_length),
+                   buff, NULL);
     else
-    {
-      sprintf(buff, "%.*f", (int) field->decimals, value);
-      end= strend(buff);
-    }
+      len= my_fcvt(value, (int) field->decimals, buff, NULL);
 
+    if (field->flags & ZEROFILL_FLAG && len < field->length &&
+        field->length < MAX_DOUBLE_STRING_REP_LENGTH - 1)
     {
-      size_t length= end - buff;
-      if (field->flags & ZEROFILL_FLAG && length < field->length &&
-          field->length < MAX_DOUBLE_STRING_REP_LENGTH - 1)
-      {
-        bmove_upp((uchar*) buff + field->length, (uchar*) buff + length,
-                  length);
-        bfill((char*) buff, field->length - length, '0');
-        length= field->length;
-      }
-      fetch_string_with_conversion(param, buff, length);
+      bmove_upp((uchar*) buff + field->length, (uchar*) buff + len,
+                len);
+      bfill((char*) buff, field->length - len, '0');
+      len= field->length;
     }
+    fetch_string_with_conversion(param, buff, len);
 
     break;
   }
@@ -3538,7 +3524,7 @@ static void fetch_datetime_with_conversion(MYSQL_BIND *param,
   {
     ulonglong value= TIME_to_ulonglong(my_time);
     fetch_float_with_conversion(param, field,
-                                ulonglong2double(value), DBL_DIG);
+                                ulonglong2double(value), MY_GCVT_ARG_DOUBLE);
     break;
   }
   case MYSQL_TYPE_TINY:
@@ -3632,7 +3618,7 @@ static void fetch_result_with_conversion(MYSQL_BIND *param, MYSQL_FIELD *field,
   {
     float value;
     float4get(value,*row);
-    fetch_float_with_conversion(param, field, value, FLT_DIG);
+    fetch_float_with_conversion(param, field, value, MY_GCVT_ARG_FLOAT);
     *row+= 4;
     break;
   }
@@ -3640,7 +3626,7 @@ static void fetch_result_with_conversion(MYSQL_BIND *param, MYSQL_FIELD *field,
   {
     double value;
     float8get(value,*row);
-    fetch_float_with_conversion(param, field, value, DBL_DIG);
+    fetch_float_with_conversion(param, field, value, MY_GCVT_ARG_DOUBLE);
     *row+= 8;
     break;
   }