add the intoverflow lib

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@9739 d7cf8633-e32d-0410-b094-e92efae38249

diff --git a/intoverflow.h b/intoverflow.h
new file mode 100644 (file)
index 0000000..df90616
--- /dev/null
+++ b/intoverflow.h
@@ -0,0 +1,22 @@
+#ifndef INTOVERFLOW_H
+#define INTOVERFLOW_H
+
+// simple safe library to handle integer overflows when doing buffer size calculations
+// Usage:
+//   - calculate data size using INTOVERFLOW_??? macros
+//   - compare: calculated-size <= INTOVERFLOW_NORMALIZE(buffersize)
+// Functionality:
+//   - all overflows (values > INTOVERFLOW_MAX) and errors are mapped to INTOVERFLOW_MAX
+//   - if any input of an operation is INTOVERFLOW_MAX, INTOVERFLOW_MAX will be returned
+//   - otherwise, regular arithmetics apply
+
+#define INTOVERFLOW_MAX 2147483647
+
+#define INTOVERFLOW_ADD(a,b) (((a) < INTOVERFLOW_MAX && (b) < INTOVERFLOW_MAX && (a) < INTOVERFLOW_MAX - (b)) ? ((a) + (b)) : INTOVERFLOW_MAX)
+#define INTOVERFLOW_SUB(a,b) (((a) < INTOVERFLOW_MAX && (b) < INTOVERFLOW_MAX && (b) <= (a))                  ? ((a) - (b)) : INTOVERFLOW_MAX)
+#define INTOVERFLOW_MUL(a,b) (((a) < INTOVERFLOW_MAX && (b) < INTOVERFLOW_MAX && (a) < INTOVERFLOW_MAX / (b)) ? ((a) * (b)) : INTOVERFLOW_MAX)
+#define INTOVERFLOW_DIV(a,b) (((a) < INTOVERFLOW_MAX && (b) < INTOVERFLOW_MAX && (b) > 0)                     ? ((a) / (b)) : INTOVERFLOW_MAX)
+
+#define INTOVERFLOW_NORMALIZE(a) (((a) < INTOVERFLOW_MAX) ? (a) : (INTOVERFLOW_MAX - 1))
+
+#endif