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, 14 insertions, 31 deletions

diff --git a/strings/decimal.c b/strings/decimal.c
index 282e7cae8ab..42dc33e5ac6 100644
--- a/strings/decimal.c
+++ b/strings/decimal.c
@@ -137,12 +137,6 @@ static const dec1 frac_max[DIG_PER_DEC1-1]={
   900000000, 990000000, 999000000,
   999900000, 999990000, 999999000,
   999999900, 999999990 };
-static double scaler10[]= {
-  1.0, 1e10, 1e20, 1e30, 1e40, 1e50, 1e60, 1e70, 1e80, 1e90
-};
-static double scaler1[]= {
-  1.0, 10.0, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9
-};
 
 #ifdef HAVE_purify
 #define sanity(d) DBUG_ASSERT((d)->len > 0)
@@ -947,33 +941,25 @@ fatal_error:
       to      - result will be stored there
 
   RETURN VALUE
-    E_DEC_OK
+    E_DEC_OK/E_DEC_OVERFLOW/E_DEC_TRUNCATED
 */
 
 int decimal2double(decimal_t *from, double *to)
 {
-  double result= 0.0;
-  int i, exp= 0;
-  dec1 *buf= from->buf;
-
-  for (i= from->intg; i > 0;  i-= DIG_PER_DEC1)
-    result= result * DIG_BASE + *buf++;
-
-  for (i= from->frac; i > 0; i-= DIG_PER_DEC1) {
-    result= result * DIG_BASE + *buf++;
-    exp+= DIG_PER_DEC1;
-  }
-
-  DBUG_PRINT("info", ("interm.: %f %d %f", result, exp,
-             scaler10[exp / 10] * scaler1[exp % 10]));
+  char strbuf[FLOATING_POINT_BUFFER], *end;
+  int len= sizeof(strbuf);
+  int rc, error;
 
-  result/= scaler10[exp / 10] * scaler1[exp % 10];
-
-  *to= from->sign ? -result : result;
+  rc = decimal2string(from, strbuf, &len, 0, 0, 0);
+  end= strbuf + len;
+  
+  DBUG_PRINT("info", ("interm.: %s", strbuf));
 
+  *to= my_strtod(strbuf, &end, &error);
+             
   DBUG_PRINT("info", ("result: %f (%lx)", *to, *(ulong *)to));
 
-  return E_DEC_OK;
+  return (rc != E_DEC_OK) ? rc : (error ? E_DEC_OVERFLOW : E_DEC_OK);
 }
 
 /*
@@ -990,13 +976,10 @@ int decimal2double(decimal_t *from, double *to)
 
 int double2decimal(double from, decimal_t *to)
 {
-  /* TODO: fix it, when we'll have dtoa */
-  char buff[400], *end;
-  int length, res;
+  char buff[FLOATING_POINT_BUFFER], *end;
+  int res;
   DBUG_ENTER("double2decimal");
-  length= my_sprintf(buff, (buff, "%.16G", from));
-  DBUG_PRINT("info",("from: %g  from_as_str: %s", from, buff));
-  end= buff+length;
+  end= buff + my_gcvt(from, MY_GCVT_ARG_DOUBLE, sizeof(buff) - 1, buff, NULL);
   res= string2decimal(buff, to, &end);
   DBUG_PRINT("exit", ("res: %d", res));
   DBUG_RETURN(res);