shared: Add some regular helpers

Imported from weston, useful when will be adding systemd-notify, and
potentially other bits. Adds MIN/MAX/container_of.

Bug-AGL: SPEC-3119

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: I2cb53784943ab3c5bdbc447611f30036f7c64e21

1 files changed, 141 insertions, 0 deletions

diff --git a/shared/helpers.h b/shared/helpers.h
new file mode 100644
index 0000000..0ebcc4a
--- /dev/null
+++ b/shared/helpers.h
@@ -0,0 +1,141 @@
+/*
+ * Copyright © 2015 Samsung Electronics Co., Ltd
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+  *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef WESTON_HELPERS_H
+#define WESTON_HELPERS_H
+
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @file
+ * Simple misc helper macros.
+ */
+
+/**
+ * Compile-time computation of number of items in a hardcoded array.
+ *
+ * @param a the array being measured.
+ * @return the number of items hardcoded into the array.
+ */
+#ifndef ARRAY_LENGTH
+#define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])
+#endif
+
+/**
+ * Returns the smaller of two values.
+ *
+ * @param x the first item to compare.
+ * @param y the second item to compare.
+ * @return the value that evaluates to lesser than the other.
+ */
+#ifndef MIN
+#define MIN(x,y) (((x) < (y)) ? (x) : (y))
+#endif
+
+/**
+ * Returns the bigger of two values.
+ *
+ * @param x the first item to compare.
+ * @param y the second item to compare.
+ * @return the value that evaluates to more than the other.
+ */
+#ifndef MAX
+#define MAX(x,y) (((x) > (y)) ? (x) : (y))
+#endif
+
+/**
+ * Returns a pointer to the containing struct of a given member item.
+ *
+ * To demonstrate, the following example retrieves a pointer to
+ * `example_container` given only its `destroy_listener` member:
+ *
+ * @code
+ * struct example_container {
+ *     struct wl_listener destroy_listener;
+ *     // other members...
+ * };
+ *
+ * void example_container_destroy(struct wl_listener *listener, void *data)
+ * {
+ *     struct example_container *ctr;
+ *
+ *     ctr = wl_container_of(listener, ctr, destroy_listener);
+ *     // destroy ctr...
+ * }
+ * @endcode
+ *
+ * @param ptr A valid pointer to the contained item.
+ *
+ * @param type A pointer to the type of content that the list item
+ * stores. Type does not need be a valid pointer; a null or
+ * an uninitialised pointer will suffice.
+ *
+ * @param member The named location of ptr within the sample type.
+ *
+ * @return The container for the specified pointer.
+ */
+#ifndef container_of
+#define container_of(ptr, type, member) ({				\
+	const __typeof__( ((type *)0)->member ) *__mptr = (ptr);	\
+	(type *)( (char *)__mptr - offsetof(type,member) );})
+#endif
+
+/**
+ * Build-time static assertion support
+ *
+ * A build-time equivalent to assert(), will generate a compilation error
+ * if the supplied condition does not evaluate true.
+ *
+ * The following example demonstrates use of static_assert to ensure that
+ * arrays which are supposed to mirror each other have a consistent
+ * size.
+ *
+ * This is only a fallback definition; support must be provided by the
+ * compiler itself.
+ *
+ * @code
+ * int small[4];
+ * long expanded[4];
+ *
+ * static_assert(ARRAY_LENGTH(small) == ARRAY_LENGTH(expanded),
+ *               "size mismatch between small and expanded arrays");
+ * for (i = 0; i < ARRAY_LENGTH(small); i++)
+ *     expanded[i] = small[4];
+ * @endcode
+ *
+ * @param condition Expression to check for truth
+ * @param msg Message to print on failure
+ */
+#ifndef static_assert
+# ifdef _Static_assert
+#  define static_assert(cond, msg) _Static_assert(cond, msg)
+# else
+#  define static_assert(cond, msg)
+# endif
+#endif
+
+#ifdef  __cplusplus
+}
+#endif
+
+#endif /* WESTON_HELPERS_H */