AssortedEuler/Euler4WithInlineX86Assembly.cpp at master · fatsmcgee/AssortedEuler · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
// AsmTest.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

int IsPal(int n){
	int digits[100];
	int i = 0;
	int isPal = 1;

	_asm {

		start:
			cmp n,0
			je check_palindrome

			//edx:eax/ebx --> eax = result, edx = remainder
			mov eax,n
			xor edx,edx
			mov ebx,10
			div ebx // eax has result, edx has the next digit

			mov n,eax

			//digits[i] = edx
			mov esi,i
			lea eax, digits
			mov [eax+4*esi],edx

			inc esi
			mov i,esi

			jmp start

		check_palindrome :

			//squeeze equality
			mov eax,i
			dec eax
			mov ebx,0

		loop_palindrome:

			cmp eax, ebx
			jle end

			mov ecx, digits[eax*4]
			mov edx, digits[ebx*4]

			//if ecx!=edx return false
			cmp ecx,edx
			jne falsify

			dec eax
			inc ebx

			jmp loop_palindrome

		falsify:
			mov isPal,0
		end:


	}
	return isPal;
}

int Euler4(){

	int largest = 0;

	_asm{
		//for eax in 100..999, for ebx in 100..999
		mov eax, 100
		mov ebx, 100

		loop_eax:
			cmp eax,1000
			jge end

		loop_ebx:
			cmp ebx,1000
			jge end_loop_ebx


			//ecx = eax; eax=eax*ebx
			mov ecx,eax
			mul ebx
			xchg eax,ecx //now eax is as before, ecx = eax*ebx


			//first save registers, then use ecx as arg
			push eax
			push ebx
			push ecx

			push ecx
			call IsPal

			//restore registers, set result to edx
			mov edx,eax
			//pop once to pop pushed argument (due to CDECL), once to start popping stored arguments
			pop ecx
			pop ecx
			pop ebx
			pop eax

			//not pal, continue
			cmp edx,1
			jne not_largest_pal

			//not largest, continue
			cmp ecx,largest
			jle not_largest_pal
			mov largest,ecx


		not_largest_pal:
			inc ebx
			jmp loop_ebx

		end_loop_ebx:
			mov ebx,100
			inc eax
			jmp loop_eax
		end:

	}

	return largest;
}

int _tmain(int argc, _TCHAR* argv[])
{
	printf("%d", Euler4());
	return 0;
}