[Python-checkins] r77450 - in python/trunk: Lib/test/floating_points.txt Misc/NEWS Python/dtoa.c

[mark.dickinson]

Author: mark.dickinson
Date: Tue Jan 12 23:23:56 2010
New Revision: 77450

Log:
Issue #7632: Fix a problem with _Py_dg_strtod that could lead to
crashes in debug builds, for certain long numeric strings
corresponding to subnormal values.


Modified:
   python/trunk/Lib/test/floating_points.txt
   python/trunk/Misc/NEWS
   python/trunk/Python/dtoa.c

Modified: python/trunk/Lib/test/floating_points.txt
==============================================================================
--- python/trunk/Lib/test/floating_points.txt	(original)
+++ python/trunk/Lib/test/floating_points.txt	Tue Jan 12 23:23:56 2010
@@ -1019,3 +1019,10 @@
 +43723334984997307E-26
 +10182419849537963E-24
 -93501703572661982E-26
+
+# A value that caused a crash in debug builds for Python >= 2.7, 3.1
+# See http://bugs.python.org/issue7632
+2183167012312112312312.23538020374420446192e-370
+
+# Another value designed to test a corner case of Python's strtod code.
+0.99999999999999999999999999999999999999999e+23

Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS	(original)
+++ python/trunk/Misc/NEWS	Tue Jan 12 23:23:56 2010
@@ -12,6 +12,10 @@
 Core and Builtins
 -----------------
 
+- Issue #7632: Fix a crash in dtoa.c that occurred in debug builds
+  when parsing certain long numeric strings corresponding to subnormal
+  values.
+
 - Issue #7319: Silence DeprecationWarning by default.
 
 - Issue #2335: Backport set literals syntax from Python 3.x.

Modified: python/trunk/Python/dtoa.c
==============================================================================
--- python/trunk/Python/dtoa.c	(original)
+++ python/trunk/Python/dtoa.c	Tue Jan 12 23:23:56 2010
@@ -1142,7 +1142,7 @@
     dsign = bc->dsign;
     nd = bc->nd;
     nd0 = bc->nd0;
-    p5 = nd + bc->e0 - 1;
+    p5 = nd + bc->e0;
     speccase = 0;
     if (rv->d == 0.) {  /* special case: value near underflow-to-zero */
         /* threshold was rounded to zero */
@@ -1227,17 +1227,21 @@
         }
     }
 
-    /* Now b/d = exactly half-way between the two floating-point values */
-    /* on either side of the input string.  Compute first digit of b/d. */
-
-    if (!(dig = quorem(b,d))) {
-        b = multadd(b, 10, 0);  /* very unlikely */
-        if (b == NULL) {
-            Bfree(d);
-            return -1;
-        }
-        dig = quorem(b,d);
+    /* Now 10*b/d = exactly half-way between the two floating-point values
+       on either side of the input string.  If b >= d, round down. */
+    if (cmp(b, d) >= 0) {
+        dd = -1;
+        goto ret;
+    }
+	
+    /* Compute first digit of 10*b/d. */
+    b = multadd(b, 10, 0);
+    if (b == NULL) {
+        Bfree(d);
+        return -1;
     }
+    dig = quorem(b, d);
+    assert(dig < 10);
 
     /* Compare b/d with s0 */