xmm | high performance third party memory manager for Go | Performance Testing library

Agree with comments: your stack alignment is incorrect.

It is true that the stack must be aligned to 16 bytes. However, the question is when? The normal rule is that the stack pointer must be a multiple of 16 at the site of a call instruction that calls an ABI-compliant function.

Well, you don't use a call instruction, but what that really means is that on entry to an ABI-compliant function, the stack pointer must be 8 less than a multiple of 16, or in other words an odd multiple of 8, since it assumes it was called with a call instruction that pushed an 8-byte return address. That is just the opposite of what your code does, and so the stack is misaligned for the rest of your program, which makes printf crash when it tries to use aligned move instructions.

You could subtract 8 from the sp computed in your C code.

Or, I'm not really sure why you go to the trouble of loading the destination address into a register, then pushing and ret, when an indirect jump or call would do. (Unless you are deliberately trying to fool the indirect branch predictor?) An indirect call will also kill the stack-alignment bird, by pushing the return address (even though it will never be used). So you could leave the rest of your code alone, and replace all the r8/ret stuff in restore_context with just

The easiest way is probably to use pshufb to permute the bytes, followed by movd to store the datum:

The encoding is as follows:

I got solution so I answered here, issue is not of flutter_ffmpeg, issue is caused because app had not permission to write in external storage to resolve this add "MANAGE_EXTERNAL_STORAGE" in mainfest.xml file and set output path is File('storage/emulated/0/my_folder/o.mp4').path , and everything works fine.

"*" won't expand in variable creation process, try it like this:

The simplest solution is to avoid the absolute address in ptr(). The reason is that x86/x86_64 requires a 32-bit displacement, which is not always possible for arbitrary user addresses - the displacement is calculated by using the current instruction pointer and the target address - if the difference is outside a signed 32-bit integer the instruction is not encodable (this is an architecture constraint).

Example code:

In which assembly flavors do I use .align instead of align?

Most notably the GNU assembler (GAS) uses .align, but every assembler can have its own syntax. You should check the manual of whatever assembler you are actually using.

Do I need to write this keyword/instruction before every data object or is there a way to write it just once?

You don't need to write it before each object if you can keep track of the alignment as you go. For instance, in your example, you wrote align 16 and then assembled 4 dwords of data, which is 16 bytes. So following that data, the current address is again aligned to 16 and another align 16 would be unnecessary (though of course harmless). You could write something like

Combine answers from How do I convert a video to GIF using ffmpeg, with reasonable quality? and Resizing videos with ffmpeg to fit into specific size.

I'd go with the interleaving approach suggested by chtz.

Read 32 or 64 bytes (aka a full cache line) from two rows, then interleave.

32 bytes at least, as the width of each row % 32 == 0, and preferably 64 bytes, as that is a full cache line and it would take 8 accumulators out of 16 registers.

Also I would guess that processing the input as blocks of (8, 16, or 32 rows) by (32 or 64 columns) would be better than processing all the rows; the more rows you process, the less you need to spill the accumulators to memory, with more rows processed in non-linear order the higher the probability of evicting soon to be needed lines from cache. 4 rows should be definitively on safe side.

Interleaving b is quite naturally done by