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%include "sys.asm"
%include "lib.asm"
%define rPosX r8
%define rPosY r9
%define rDirX r10
%define rDirY r11
global _start
_start:
sub rsp, 4096
syscall SYS_READ, FD_STDIN, rsp, 4096
mov rdi, rax ;; Length.
xor rcx, rcx ;; Index.
xor rPosX, rPosX
xor rPosY, rPosY
xor rDirX, rDirX
mov rDirY, -1 ;; North.
.loopTurn:
cmp byte [rsp + rcx], 'L'
jne .right
.left: ;; L(dx, dy) = (dy, -dx)
neg rDirX
jmp .swap
.right: ;; R(dx, dy) = (-dy, dx)
neg rDirY
.swap:
xchg rDirX, rDirY
xor rax, rax
.loopDigit:
inc rcx
movzx rdx, byte [rsp + rcx]
cmp dl, '0'
jb .breakDigit
;; rax = rax * 10 + rdx - '0'
shl rax, 1
lea rax, [rax + rax * 4 - '0']
add rax, rdx
jmp .loopDigit
.breakDigit:
add rcx, 2 ;; Discard comma and space.
mov rdx, rax
imul rdx, rDirX
add rPosX, rdx
mov rdx, rax
imul rdx, rDirY
add rPosY, rdx
cmp rcx, rdi
jb .loopTurn
;; abs(x) = (x ^ (x >> 63)) - (x >> 63)
mov rax, rPosX
sar rax, 63
xor rPosX, rax
sub rPosX, rax
mov rax, rPosY
sar rax, 63
xor rPosY, rax
sub rPosY, rax
lea rdi, [rPosX + rPosY]
call hex32
push rax
syscall SYS_WRITE, FD_STDOUT, rsp, 8
xor rax, rax
syscall SYS_EXIT, rax
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