• captaindet (6/6) Jun 28 2016 is there an alignment guarantee for core.stdc.stdlib.malloc?
• Hiemlick Hiemlicker (21/28) Jun 28 2016 Yes, the C standard requires malloc to be aligned to the platform
• captaindet (2/4) Jun 28 2016 just what i was hopping for. thanks!

captaindet <2krnk gmx.net> writes:

is there an alignment guarantee for core.stdc.stdlib.malloc?

more specifically, using DMD and compiling for 32bit on windows, can i 
assume proper alignment for int or uint variables?

background: i like to re-use a (ubyte) buffer, sometimes it will store 
only bytes, sometimes it shall store uints.

thanks

Hiemlick Hiemlicker <HH reign.com> writes:

On Wednesday, 29 June 2016 at 02:24:55 UTC, captaindet wrote:
 is there an alignment guarantee for core.stdc.stdlib.malloc?

 more specifically, using DMD and compiling for 32bit on 
 windows, can i assume proper alignment for int or uint 
 variables?

 background: i like to re-use a (ubyte) buffer, sometimes it 
 will store only bytes, sometimes it shall store uints.

 thanks

Yes, the C standard requires malloc to be aligned to the platform 
size(4 for 32bit, 8 for 64-bit).

Alternatively, you can use code like

		size_t capacity = capacity;
		size_t size = T.sizeof*capacity;
		enforce(size > 0, "Cannot allocate fixed array of size 0.");
		if (mem is null)
			mem = cast(T*)malloc(size+Alignment);
		else
			mem = cast(T*)realloc(mem, size+Alignment);

		enforce(cast(int)mem > 0, "Could not malloc memory block.");
		
		// Adjust memory pointer to be aligned
		size_t tmp = (cast(size_t)mem) & (Alignment - 1);
		size_t ofs = (Alignment - tmp) & (Alignment - 1);
		mem = cast(T*)((cast(size_t)mem) + ofs);
		
		// Add extra space to be additional end capacity.
		capacity = cast(size_t)((size + Alignment - ofs)/T.sizeof);

which malloc's a block of memory and aligns it.

captaindet <2krnk gmx.net> writes:

On 2016-06-29 14:39, Hiemlick Hiemlicker wrote:
 Yes, the C standard requires malloc to be aligned to the platform size(4
 for 32bit, 8 for 64-bit).

just what i was hopping for. thanks!