[FFmpeg-devel] [PATCH] install aes.h, des.h and rc4.h

[Reimar Döffinger]

On Fri, Feb 06, 2009 at 11:38:53PM +0100, Michael Niedermayer wrote:
> On Fri, Feb 06, 2009 at 11:18:57PM +0100, Reimar D?ffinger wrote:
> > On Fri, Feb 06, 2009 at 10:33:00PM +0100, Michael Niedermayer wrote:
> > > On Fri, Feb 06, 2009 at 09:53:16PM +0100, Reimar D?ffinger wrote:
> > > > But maybe we can find a better solution.
> > > > What about a
> > > > void *av_alloca(uint8_t *);
> > > > Usage would be
> > > > uint8_t buffer[size + AV_ALLOCA_PADDING];
> > > > struct AVAES *a = av_alloca(buffer);
> > > > 
> > > > Does that seem like it might make a good solution or does it have
> > > > serious issues?
> > > 
> > > its not particularely pretty and something should be done to make it
> > > less error prone, also no function call should happen just a macro
> > >  or inline function
> > 
> > I did intend to make the function static inline.
> > I think it will always ugly, though maybe something like (untested)
> > #define AV_STACK_VAR(type, name, size) \
> >     uint8_t name ff_alloca_##name##_buffer[size + 16]; \
> >     type name = ff_alloca_##name##_buffer + ((-(long)ff_alloca_##name##_buffer - 1)&15) + 1;
> > 
> > fits your idea better?
> 
> type name = ff_alloca_##name##_buffer + ((-(long)ff_alloca_##name##_buffer)&15);
> and +15 should be enough

I was too tired to think about it so I just copy-and-pasted the malloc
stuff.
So like this (note the ugly casting is to make sure it works with C++ as
well, and I haven't tested it yet):
Index: libavutil/mem.h
===================================================================
--- libavutil/mem.h     (revision 16989)
+++ libavutil/mem.h     (working copy)
@@ -41,6 +41,17 @@
 #endif
 
 /**
+ * Allocate data on the stack with sufficient alignment for all operations
+ * and assign it to the given variable.
+ * @param type type of the created variable, must be a pointer type
+ * @param name name of the created variable
+ * @param size Size in bytes for the memory block to be allocated.
+ */
+#define AV_STACK_VAR(type, name, size) \
+    uint8_t ff_alloca_##name##_buffer[size + 15]; \
+    type name = (type)(void *)(ff_alloca_##name##_buffer + ((-(long)ff_alloca_##name##_buffer)&15));
+
+/**
  * Allocates a block of \p size bytes with alignment suitable for all
  * memory accesses (including vectors if available on the CPU).
  * @param size Size in bytes for the memory block to be allocated.