Add 2015 - Day 1 - Part 2

2015/01/main.asm

@@ -8,37 +8,60 @@ global _walkFloors
 _walkFloors:
   enter 0,0
   push ebx
+  push edi
+
+  ; [ ebp +  8 ] = int currentFloor
+  ; [ ebp + 12 ] = int* totalInstructionCounter
+  ; [ ebp + 16 ] = int* firstEnteredBasement
+  ; [ ebp + 20 ] = char* instructions
+  ; [ ebp + 24 ] = size_t instructionCount
 
   mov eax, [ ebp +  8 ] ; eax = currentFloor
-  mov edx, [ ebp + 12 ] ; edx = char* instructions
-  mov ecx, [ ebp + 16 ] ; ecx = size_t instructionCount
-
-  jcxz .end ; skip to end if there are no instructions
-
-  inc ecx ; increment instruction count by 1
-          ; because loop instruction uses prefix decrement
+  mov edx, [ ebp + 20 ] ; edx = instructions
+  xor ecx, ecx          ; ecx = 0
 
 .instructionLoop:
+  cmp ecx, [ ebp + 24 ] ; check if we went past instructionCount
+  jge .end              ; if so, we are done here
+  inc ecx               ; otherwise, increment instruction counter and continue
+
   mov bl, [ edx ] ; bl = instructions[edx]
   inc edx         ; edx++
 
-  cmp bl, '('     ; left parenthesis...
-  je .moveUpFloor ; moves up a floor
-
+  cmp bl, '('       ; left parenthesis...
+  je .moveUpFloor   ; moves up a floor
   cmp bl, ')'       ; right parenthesis...
   je .moveDownFloor ; moves down a floor
-
-  jmp .end ; unknown character skips to the end
+  jmp .end          ; unknown character skips to the end
 
 .moveUpFloor:
   inc eax
-  loop .instructionLoop
+  jmp .instructionLoop
 
 .moveDownFloor:
   dec eax
-  loop .instructionLoop
+  cmp eax, -1 ; check if we entered the basement
+  je .onEnteredBasement
+  jmp .instructionLoop
+
+ .onEnteredBasement:
+  mov ebx, [ ebp + 16 ] ; ebx = &firstEnteredBasement
+  cmp dword [ ebx ], -1 ; check if firstEnteredBasement has not been set yet
+  jne .instructionLoop  ; if it was already set, go to next instruction
+
+  mov edi, [ ebp + 12 ]  ; edi = &totalInstructionCounter
+  mov edi, [ edi ]       ; edi = totalInstructionCounter
+  add edi, ecx           ; add current instruction counter to the total
+  mov dword [ ebx ], edi ; set firstEnteredBasement to the total
+  jmp .instructionLoop
 
 .end:
+  mov edi, [ ebp + 12 ]  ; edi = &totalInstructionCounter
+  mov ebx, [ edi ]       ; ebx = totalInstructionCounter
+  add ebx, ecx           ; add current instruction counter to the total
+  mov dword [ edi ], ebx ; set totalInstructionCounter to the new total
+
+  pop edi
   pop ebx
   leave
   ret

2015/01/main.c

@@ -2,7 +2,7 @@
 
 #define BUFFER_SIZE 256
 
-int walkFloors(int currentFloor, char* instructions, size_t instructionCount);
+int walkFloors(int currentFloor, int* totalInstructionCounter, int* firstEnteredBasement, char* instructions, size_t instructionCount);
 
 int main() {
 	FILE* file;
@@ -13,6 +13,8 @@ int main() {
 	}
 	
 	int floor = 0;
+	int totalInstructionCounter = 0;
+	int firstEnteredBasement = -1;
 	
 	char buffer[BUFFER_SIZE];
 	while (!feof(file)) {
@@ -24,10 +26,11 @@ int main() {
 			return 1;
 		}
 		
-		floor = walkFloors(floor, buffer, readBytes);
+		floor = walkFloors(floor, &totalInstructionCounter, &firstEnteredBasement, buffer, readBytes);
 	}
 	
 	fclose(file);
-	printf("Final floor: %d", floor);
+	printf("Final floor: %d\n", floor);
+	printf("First entered basement: %d\n", firstEnteredBasement);
 	return 0;
 }