bk commit into 5.0 tree (hartmut:1.2296) BUG#23260

['Hartmut Holzgraefe']

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ChangeSet@stripped, 2006-11-10 19:54:01+01:00, hartmut@stripped +1 -0
  Alternative decimal2double implementation using an algorithm 
  more similar to my_strtod() (and maybe even a bit faster due
  to less floating point divisions) 
  This should at least partially fix Bug #23260 for DECIMALs
  with a moderate number of total digits

  strings/decimal.c@stripped, 2006-11-10 19:53:54+01:00, hartmut@stripped +26 -9
    Alternative decimal2double implementation using an algorithm 
    more similar to my_strtod() (and maybe even a bit faster due
    to less floating point divisions) 
    This should at least partially fix Bug #23260 for DECIMALs
    with a moderate number of total digits

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	hartmut
# Host:	linux.site
# Root:	/home/hartmut/projects/mysql/dev/5.0

--- 1.70/strings/decimal.c	2006-11-10 19:54:11 +01:00
+++ 1.71/strings/decimal.c	2006-11-10 19:54:11 +01:00
@@ -138,6 +138,12 @@
   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)
@@ -946,15 +952,26 @@
 
 int decimal2double(decimal_t *from, double *to)
 {
-  double x=0, t=DIG_BASE;
-  int intg, frac;
-  dec1 *buf=from->buf;
-
-  for (intg=from->intg; intg > 0; intg-=DIG_PER_DEC1)
-    x=x*DIG_BASE + *buf++;
-  for (frac=from->frac; frac > 0; frac-=DIG_PER_DEC1, t*=DIG_BASE)
-    x+=*buf++/t;
-  *to=from->sign ? -x : x;
+  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]));
+
+  result/= scaler10[exp/10]*scaler1[exp%10];
+
+  *to = from->sign ? -result : result;
+
+  DBUG_PRINT("info", ("result: %f (%lx)", *to, *to));
+
   return E_DEC_OK;
 }