#Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, using a clever calling convention for a 1 byte solution.

Meta: Writing input to registers, Writing output to registers

Other resources: Agner Fog's notes on calling conventions

Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, using a clever calling convention for a 1 byte solution.

Meta: Writing input to registers, Writing output to registers

Other resources: Agner Fog's notes on calling conventions

#Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, using a clever calling convention for a 1 byte solution.

Other resources: Agner Fog's notes on calling conventions

#Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, using a clever calling convention for a 1 byte solution.

Meta: Writing input to registers, Writing output to registers

Other resources: Agner Fog's notes on calling conventions

#Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, in which Peter Cordes uses a clever calling convention for a 1 byte solution.

#Use whatever calling conventions are convenient

System V x86 uses the stack and System V x86-64 uses rdi, rsi, rdx, rcx, etc. for input parameters, and rax as the return value, but it is perfectly reasonable to use your own calling convention. __fastcall uses ecx and edx as input parameters, and other compilers/OSes use their own conventions. Use the stack and whatever registers as input/output when convenient.

Example: The repetitive byte counter, using a clever calling convention for a 1 byte solution.

Other resources: Agner Fog's notes on calling conventions