Will SETEND speed up dolphin on ARM (Android)?

07-01-2018, 05:59 PM #1

Hi,

I was wondering if using the ARM SETEND BE/LE instructions (check this page) to load/store 16,32 & 64 bit values from memory will speed up the emulation on arm CPU? I think using SETEND BE/LE will save a few CPU ticks because the swapping is not needed anymore (unless SETEND BE/LE takes more than swapping).

**degasus** · 07-03-2018, 06:06 PM #2

This actually sounds like a nice instruction, but it is only available in the 32bit mode. And we can't switch between 32bit and 64bit within the same application. So we either loose fastmem + half of our registers, or this instruction.

07-03-2018, 08:36 PM #3

(07-03-2018, 06:06 PM)degasus Wrote: This actually sounds like a nice instruction, but it is only available in the 32bit mode. And we can't switch between 32bit and 64bit within the same application. So we either loose fastmem + half of our registers, or this instruction.

Ah, you're right PSTATE has no endian bit. I don't know why they didn't support it in 64bit mode as long as the CPU supports it in 32 bit mode...

07-03-2018, 09:42 PM #4

It seems there is a way to set the endians also on AArch64 but it seems is not mandatory so, some AArch64 CPU might not implement it....

**degasus** · 07-03-2018, 09:46 PM #5

Yeah, you can still pick LE or BE, but only in real mode. Se we would have to ask the operation system to switch the ABI. Right now, linux doesn't support this but on application init.