276 lines
5.7 KiB
NASM
276 lines
5.7 KiB
NASM
bits 64
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default rel
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section .text
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extern print
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extern malloc
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extern free
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global part1
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part1:
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push rbp
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mov rbp, rsp
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push rbx
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push r12
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push r13
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push r14
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push r15
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sub rsp, 32
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call findCoordinateRanges
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call allocateGridArray
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call zeroGridArray
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call deliverPresents
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mov rcx, r13
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call free
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lea rcx, [ print_houses_with_at_least_one_present ]
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mov rdx, r12
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call print
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add rsp, 32
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pop r15
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pop r14
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pop r13
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pop r12
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pop rbx
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leave
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ret
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findCoordinateRanges:
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; TMP | rbx = value of current character of input string
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; IN | rcx = pointer to current character of input string
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; TMP | r8 = x coordinate
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; TMP | r9 = y coordinate
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; OUT | r10 = minimum x
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; OUT | r11 = minimum y
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; OUT | r12 = maximum x
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; OUT | r13 = maximum y
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; TMP | r14 = next x offset
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; TMP | r15 = next y offset
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push rcx ; remember the beginning of the input string
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xor r8, r8
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xor r9, r9
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xor r10, r10
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xor r11, r11
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xor r12, r12
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xor r13, r13
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xor r14, r14
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xor r15, r15
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.nextChar:
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movzx rbx, byte [ rcx ] ; read current character
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inc rcx ; move to next character
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cmp bl, '^'
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je .goUp
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cmp bl, 'v'
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je .goDown
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cmp bl, '<'
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je .goLeft
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cmp bl, '>'
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je .goRight
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pop rcx ; for any other character, reset rcx to the beginning of the input string...
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ret ; and return from the procedure
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.goUp:
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xor r14, r14
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mov r15, -1
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jmp .updateCoordinates
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.goDown:
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xor r14, r14
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mov r15, 1
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jmp .updateCoordinates
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.goLeft:
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mov r14, -1
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xor r15, r15
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jmp .updateCoordinates
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.goRight:
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mov r14, 1
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xor r15, r15
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; fall through
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.updateCoordinates:
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add r8, r14 ; add x offset to the x coordinate
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add r9, r15 ; add y offset to the y coordinate
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cmp r10, r8 ; compare the minimum x with the current x coordinate
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cmovg r10, r8 ; if the minimum is greater than x, set it to x
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cmp r11, r9 ; compare the minimum y with the current y coordinate
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cmovg r11, r9 ; if the minimum is greater than y, set it to y
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cmp r12, r8 ; compare the maximum x with the current x coordinate
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cmovl r12, r8 ; if the maximum is lesser than x, set it to x
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cmp r13, r9 ; compare the maximum y with the current y coordinate
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cmovl r13, r9 ; if the maximum is lesser than y, set it to y
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jmp .nextChar
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allocateGridArray:
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; TMP | rax = reserved for math
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; IN | rcx = pointer to current character of input string
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; OUT | r8 = width of the grid
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; OUT | r9 = height of the grid
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; IN | r10 = minimum x
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; OUT | r10 = x coordinate where Santa starts
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; IN | r11 = minimum y
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; OUT | r11 = y coordinate where Santa starts
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; IN | r12 = maximum x
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; IN | r13 = maximum y
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; OUT | r13 = pointer to beginning of grid array (2 bytes per cell)
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; OUT | r14 = total size of the grid array in bytes
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mov r8, r12 ; r8 = maximum x
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sub r8, r10 ; r8 -= minimum x
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inc r8 ; r8 += 1
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mov r9, r13 ; r9 = maximum y
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sub r9, r11 ; r9 -= minimum y
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inc r9 ; r9 += 1
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mov rax, r8
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mul r9 ; rax = total width times total height, i.e. total grid area
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add rax, rax ; rax = rax * 2 to store up to 2 bytes per grid cell
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neg r10 ; Santa's new center on the x axis is the negated value of minimum x
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neg r11 ; Santa's new center on the y axis is the negated value of minimum y
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push rcx
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push r8
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push r9
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push r10
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push r11
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push rax ; grid array size will be popped into r14 later
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sub rsp, 8
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mov rcx, rax
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call malloc ; allocate grid array and store a pointer to the beginning in rax
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mov r13, rax ; move grid pointer to r13
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add rsp, 8
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pop r14
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pop r11
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pop r10
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pop r9
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pop r8
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pop rcx
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ret
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zeroGridArray:
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; TMP | rax = pointer to current position in the grid array
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; IN | r13 = pointer to beginning of grid array (2 bytes per cell)
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; IN | r14 = total size of the grid array in bytes
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; TMP | r15 = remaining bytes to clear
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mov rax, r13
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mov r15, r14
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.loop:
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cmp r15, 0
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jle .done
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mov byte [ rax ], 0
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inc rax
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dec r15
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jmp .loop
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.done:
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ret
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deliverPresents:
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; TMP | rax = offset in the grid array
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; TMP | rbx = value of current character of input string
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; IN | rcx = pointer to current character of input string
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; IN | r8 = width of the grid
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; IN | r9 = height of the grid
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; IN | r10 = x coordinate, initially set to where Santa starts
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; IN | r11 = y coordinate, initially set to where Santa starts
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; OUT | r12 = amount of houses that received at least one present
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; IN | r13 = pointer to beginning of grid array (2 bytes per cell)
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; TMP | r14 = next x offset
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; TMP | r15 = next y offset
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xor r12, r12
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jmp .deliverPresent ; deliver first present to house at Santa's current location
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.nextChar:
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movzx rbx, byte [ rcx ] ; read current character
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inc rcx ; move to next character
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cmp bl, '^'
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je .goUp
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cmp bl, 'v'
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je .goDown
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cmp bl, '<'
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je .goLeft
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cmp bl, '>'
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je .goRight
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ret ; for any other character, return from the procedure
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.goUp:
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xor r14, r14
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mov r15, -1
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jmp .moveAndDeliverPresent
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.goDown:
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xor r14, r14
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mov r15, 1
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jmp .moveAndDeliverPresent
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.goLeft:
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mov r14, -1
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xor r15, r15
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jmp .moveAndDeliverPresent
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.goRight:
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mov r14, 1
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xor r15, r15
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; fall through
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.moveAndDeliverPresent:
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add r10, r14 ; add x offset to the x coordinate
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add r11, r15 ; add y offset to the y coordinate
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.deliverPresent:
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mov rax, r11 ; rax = y
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mul r8 ; y * grid width
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add rax, r10 ; y * grid width + x
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add rax, rax ; double the offset because every cell is 2 bytes
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inc word [ r13 + rax ]
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cmp word [ r13 + rax ], 1
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je .firstPresentForHouse
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jmp .nextChar
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.firstPresentForHouse:
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inc r12
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jmp .nextChar
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section .data
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print_houses_with_at_least_one_present: db `Total houses with at least one present: %d\n`, 0
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