diff -r 60cb72c7fd75 Modules/_sre.c
--- a/Modules/_sre.c	Sun Mar 10 09:51:37 2013 -0700
+++ b/Modules/_sre.c	Mon Mar 11 10:34:30 2013 -0400
@@ -655,7 +655,7 @@
     alloc_pos = state->data_stack_base; \
     TRACE(("allocating %s in %d (%d)\n", \
            SFY(type), alloc_pos, sizeof(type))); \
-    if (state->data_stack_size < alloc_pos+sizeof(type)) { \
+    if (sizeof(type) > state->data_stack_size - alloc_pos) { \
         int j = data_stack_grow(state, sizeof(type)); \
         if (j < 0) return j; \
         if (ctx_pos != -1) \
@@ -675,7 +675,7 @@
 do { \
     TRACE(("copy data in %p to %d (%d)\n", \
            data, state->data_stack_base, size)); \
-    if (state->data_stack_size < state->data_stack_base+size) { \
+    if (size > state->data_stack_size - state->data_stack_base) { \
         int j = data_stack_grow(state, size); \
         if (j < 0) return j; \
         if (ctx_pos != -1) \
@@ -997,7 +997,7 @@
             TRACE(("|%p|%p|REPEAT_ONE %d %d\n", ctx->pattern, ctx->ptr,
                    ctx->pattern[1], ctx->pattern[2]));
 
-            if (ctx->ptr + state->charsize * ctx->pattern[1] > end)
+            if (ctx->pattern[1] > (end - ctx->ptr) / state->charsize)
                 RETURN_FAILURE; /* cannot match */
 
             state->ptr = ctx->ptr;
@@ -1081,7 +1081,7 @@
             TRACE(("|%p|%p|MIN_REPEAT_ONE %d %d\n", ctx->pattern, ctx->ptr,
                    ctx->pattern[1], ctx->pattern[2]));
 
-            if (ctx->ptr + state->charsize * ctx->pattern[1] > end)
+            if (ctx->pattern[1] > (end - ctx->ptr) / state->charsize)
                 RETURN_FAILURE; /* cannot match */
 
             state->ptr = ctx->ptr;
@@ -2779,7 +2779,7 @@
         skip = *code;                                   \
         VTRACE(("%lu (skip to %p)\n",                   \
                (unsigned long)skip, code+skip));        \
-        if (code+skip-adj < code || code+skip-adj > end)\
+        if (skip-adj > end-code)                        \
             FAIL;                                       \
         code++;                                         \
     } while (0)
@@ -2812,7 +2812,7 @@
 
         case SRE_OP_CHARSET:
             offset = 32/sizeof(SRE_CODE); /* 32-byte bitmap */
-            if (code+offset < code || code+offset > end)
+            if (offset > end-code)
                 FAIL;
             code += offset;
             break;
@@ -2820,7 +2820,7 @@
         case SRE_OP_BIGCHARSET:
             GET_ARG; /* Number of blocks */
             offset = 256/sizeof(SRE_CODE); /* 256-byte table */
-            if (code+offset < code || code+offset > end)
+            if (offset > end-code)
                 FAIL;
             /* Make sure that each byte points to a valid block */
             for (i = 0; i < 256; i++) {
@@ -2829,7 +2829,7 @@
             }
             code += offset;
             offset = arg * 32/sizeof(SRE_CODE); /* 32-byte bitmap times arg */
-            if (code+offset < code || code+offset > end)
+            if (offset > end-code)
                 FAIL;
             code += offset;
             break;
@@ -2980,11 +2980,11 @@
                     GET_ARG; prefix_len = arg;
                     GET_ARG;
                     /* Here comes the prefix string */
-                    if (code+prefix_len < code || code+prefix_len > newcode)
+                    if (prefix_len > newcode-code)
                         FAIL;
                     code += prefix_len;
                     /* And here comes the overlap table */
-                    if (code+prefix_len < code || code+prefix_len > newcode)
+                    if (prefix_len > newcode-code)
                         FAIL;
                     /* Each overlap value should be < prefix_len */
                     for (i = 0; i < prefix_len; i++) {
@@ -3113,7 +3113,7 @@
                to allow arbitrary jumps anywhere in the code; so we just look
                for a JUMP opcode preceding our skip target.
             */
-            if (skip >= 3 && code+skip-3 >= code &&
+            if (skip >= 3 && skip-3 < end-code &&
                 code[skip-3] == SRE_OP_JUMP)
             {
                 VTRACE(("both then and else parts present\n"));