Fix for Bug 223739 to get rid of floating point equality test.

Sorry for delaying this fix for months; I hadn't noticed that it had been reviewed!

2 files changed, 29 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 451a49d..8727893 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2002-04-22  Donal K. Fellows  <fellowsd@cs.man.ac.uk>
+
+	* generic/tkTextDisp.c (GetXView,GetYView): Comparison with
+	previous values of scrollbar range are now done in a way that is
+	sensitive to the bizarreness of floating-point on architectures
+	where IEEE-FP is not used on the processor.  Also increased the
+	size of the temporary buffer to take account of the fact that
+	TCL_DOUBLE_SPACE is meant to only imply enough space to take a
+	printed double and trailing '\0', and no more.  [Bug #223739]
+	(FP_EQUAL_SCALE): New macro to help compare floating-point numbers
+	for equality in a sane way, used in GetXView and GetYView.
+
 2002-04-12  Jeff Hobbs  <jeffh@ActiveState.com>
 
 	* generic/tkWindow.c (TkCloseDisplay): Added to centralize where a
diff --git a/generic/tkTextDisp.c b/generic/tkTextDisp.c
index e0d1d57..2a3cf44 100644
--- a/generic/tkTextDisp.c
+++ b/generic/tkTextDisp.c
@@ -11,7 +11,7 @@
  * See the file "license.terms" for information on usage and redistribution
  * of this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tkTextDisp.c,v 1.9 2000/01/06 02:18:59 hobbs Exp $
+ * RCS: @(#) $Id: tkTextDisp.c,v 1.10 2002/04/22 12:45:49 dkf Exp $
  */
 
 #include "tkPort.h"
@@ -96,6 +96,16 @@ typedef struct TextStyle {
         && ((s1)->sValuePtr->bgStipple == (s2)->sValuePtr->bgStipple))
 
 /*
+ * The following macro is used to compare two floating-point numbers
+ * to within a certain degree of scale.  Direct comparison fails on
+ * processors where the processor and memory representations of FP
+ * numbers of a particular precision is different (e.g. Intel)
+ */
+
+#define FP_EQUAL_SCALE(double1, double2, scaleFactor) \
+    (fabs((double1)-(double2))*((scaleFactor)+1.0) < 0.3)
+
+/*
  * The following structure describes one line of the display, which may
  * be either part or all of one line of the text.
  */
@@ -3865,7 +3875,7 @@ GetXView(interp, textPtr, report)
 					 * scrollbar if it has changed. */
 {
     TextDInfo *dInfoPtr = textPtr->dInfoPtr;
-    char buffer[TCL_DOUBLE_SPACE * 2];
+    char buffer[TCL_DOUBLE_SPACE * 2 + 1];
     double first, last;
     int code;
 
@@ -3886,7 +3896,8 @@ GetXView(interp, textPtr, report)
 	Tcl_SetResult(interp, buffer, TCL_VOLATILE);
 	return;
     }
-    if ((first == dInfoPtr->xScrollFirst) && (last == dInfoPtr->xScrollLast)) {
+    if (FP_EQUAL_SCALE(first, dInfoPtr->xScrollFirst, dInfoPtr->maxLength) &&
+	FP_EQUAL_SCALE(last,  dInfoPtr->xScrollLast,  dInfoPtr->maxLength)) {
 	return;
     }
     dInfoPtr->xScrollFirst = first;
@@ -3936,7 +3947,7 @@ GetYView(interp, textPtr, report)
 					 * scrollbar if it has changed. */
 {
     TextDInfo *dInfoPtr = textPtr->dInfoPtr;
-    char buffer[TCL_DOUBLE_SPACE * 2];
+    char buffer[TCL_DOUBLE_SPACE * 2 + 1];
     double first, last;
     DLine *dlPtr;
     int totalLines, code, count;
@@ -3971,7 +3982,8 @@ GetYView(interp, textPtr, report)
 	Tcl_SetResult(interp, buffer, TCL_VOLATILE);
 	return;
     }
-    if ((first == dInfoPtr->yScrollFirst) && (last == dInfoPtr->yScrollLast)) {
+    if (FP_EQUAL_SCALE(first, dInfoPtr->yScrollFirst, totalLines) &&
+	FP_EQUAL_SCALE(last,  dInfoPtr->yScrollLast,  totalLines)) {
 	return;
     }
     dInfoPtr->yScrollFirst = first;