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[Qemu-devel] [PATCH for-2.11?] osdep.h: Make TIME_MAX handle different t
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH for-2.11?] osdep.h: Make TIME_MAX handle different time_t types |
Date: |
Thu, 23 Nov 2017 15:56:38 +0000 |
In our various supported host OSes, the time_t type may be either 32
or 64 bit, and could in theory also be either signed or unsigned.
Notably, in OpenBSD time_t is a 64 bit type even if 'long' is 32
bits, so using LONG_MAX for TIME_MAX is incorrect.
Use an approach suggested by Paolo Bonzini which calculates
the maximum value of the type rather than hardcoding it;
to do this we use the TYPE_MAXIMUM macro from Gnulib.
Suggested-by: Paolo Bonzini <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
---
include/qemu/osdep.h | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 281782d..e8568a0 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -147,8 +147,35 @@ extern int daemon(int, int);
#if !defined(ESHUTDOWN)
#define ESHUTDOWN 4099
#endif
+
+/* time_t may be either 32 or 64 bits depending on the host OS, and
+ * can be either signed or unsigned, so we can't just hardcode a
+ * specific maximum value. This is not a C preprocessor constant,
+ * so you can't use TIME_MAX in an #ifdef, but for our purposes
+ * this isn't a problem.
+ */
+
+/* The macros TYPE_SIGNED, TYPE_WIDTH, and TYPE_MAXIMUM are from
+ * Gnulib, and are under the LGPL v2.1 or (at your option) any
+ * later version.
+ */
+
+/* True if the real type T is signed. */
+#define TYPE_SIGNED(t) (!((t)0 < (t)-1))
+
+/* The width in bits of the integer type or expression T.
+ * Padding bits are not supported.
+ */
+#define TYPE_WIDTH(t) (sizeof(t) * CHAR_BIT)
+
+/* The maximum and minimum values for the integer type T. */
+#define TYPE_MAXIMUM(t) \
+ ((t) (!TYPE_SIGNED(t) \
+ ? (t)-1 \
+ : ((((t)1 << (TYPE_WIDTH(t) - 2)) - 1) * 2 + 1)))
+
#ifndef TIME_MAX
-#define TIME_MAX LONG_MAX
+#define TIME_MAX TYPE_MAXIMUM(time_t)
#endif
/* HOST_LONG_BITS is the size of a native pointer in bits. */
--
2.7.4
- [Qemu-devel] [PATCH for-2.11?] osdep.h: Make TIME_MAX handle different time_t types,
Peter Maydell <=