Changeset 2306 in vbox for trunk

Timestamp:

Apr 21, 2007 8:50:41 PM (18 years ago)

Author:

vboxsync

svn:sync-xref-src-repo-rev:

20673

Message:

r=frank

File:

• trunk/src/VBox/Runtime/testcase/tstInlineAsm.cpp (modified) (3 diffs)

trunk/src/VBox/Runtime/testcase/tstInlineAsm.cpp

@@ -825 +825 @@
     CHECKVAL(u64, UINT64_C(0x924719355cd35a27), "%#018RX64");
 
-#if 0 /* question is whether this should trap or not */
-      /*
-       * r=frank: Of course it must trap:
+#if 0 /* bird: question is whether this should trap or not:
+       *
+       * frank: Of course it must trap:
        *
        *   0xfffffff8 * 0x77d7daf8 = 0x77d7daf441412840
@@ -837 +837 @@
        *
        * which is definitely greater than  0x3b9aca00.
-       */
-      /* 
+       *
        * bird: No, the C version does *not* crash. So, the question is whether there any
        * code depending on it not crashing.
@@ -844 +843 @@
        * Of course the assembly versions of the code crash right now for the reasons you've
        * given, but the the 32-bit MSC version does not crash.
+       *
+       * frank: The C version does not crash but delivers incorrect results for this case.
+       * The reason is
+       *
+       *   u.s.Hi = (unsigned long)(u64Hi / u32C);
+       *
+       * Here the division is actually 64-bit by 64-bit but the 64-bit result is truncated
+       * to 32 bit. If using this (optimized and fast) function we should just be sure that
+       * the operands are in a valid range.
        */
     u64 = ASMMultU64ByU32DivByU32(UINT64_C(0xfffffff8c65d6731), UINT32_C(0x77d7daf8), UINT32_C(0x3b9aca00));