On Tuesday, 31 May 2016 at 18:52:16 UTC, Marco Leise wrote:
The 'this' pointer is usually in some register already. On Linux 32-bit for example it is in EAX, on Linux 64-bit is in RDI.
The AX register seems like a bad choice, since you require the AX/DX registers when you do multiplication and division (although all other registers are general purpose some instructions are still tied to specific registers). SI/DI are a much better choice.
By the way, you are right that 32-bit does not have access to 64-bit machine words (actually kind of obvious), but your idea wasn't far fetched, since there is the X32 architecture at least for Linux. It uses 64-bit machine words, but 32-bit pointers and allows for compact and fast programs.
As i recall the switch to use the larger registers is a simple switch per instruction, something like either 60h, 66h or 67h. I forget which one exactly, as i recall writing assembly programs using 16bit DOS but using 32bit registers using that trick (built into the assembler). Although to use the lower registers by themselves required the same switch, so...
