calculate log2

log2.c

#include <stdio.h>

#define REPEAT0(x) x
#define REPEAT1(x) REPEAT0(x), REPEAT0(x)
#define REPEAT2(x) REPEAT1(x), REPEAT1(x)
#define REPEAT3(x) REPEAT2(x), REPEAT2(x)
#define REPEAT4(x) REPEAT3(x), REPEAT3(x)
#define REPEAT5(x) REPEAT4(x), REPEAT4(x)
#define REPEAT6(x) REPEAT5(x), REPEAT5(x)
#define REPEAT7(x) REPEAT6(x), REPEAT6(x)
#define REPEAT8(x) REPEAT7(x), REPEAT7(x)
#define REPEAT9(x) REPEAT8(x), REPEAT8(x)
#define REPEAT10(x) REPEAT9(x), REPEAT9(x)
#define REPEAT11(x) REPEAT10(x), REPEAT10(x)
#define REPEAT12(x) REPEAT11(x), REPEAT11(x)
#define REPEAT13(x) REPEAT12(x), REPEAT12(x)
#define REPEAT14(x) REPEAT13(x), REPEAT13(x)
#define REPEAT15(x) REPEAT14(x), REPEAT14(x)
#define REPEAT16(x) REPEAT15(x), REPEAT15(x)
#define REPEAT17(x) REPEAT16(x), REPEAT16(x)
#define REPEAT18(x) REPEAT17(x), REPEAT17(x)
#define REPEAT19(x) REPEAT18(x), REPEAT18(x)

#define LG1 0, 0
#define LG2 LG1, REPEAT1(1)
#define LG3 LG2, REPEAT2(2)
#define LG4 LG3, REPEAT3(3)
#define LG5 LG4, REPEAT4(4)
#define LG6 LG5, REPEAT5(5)
#define LG7 LG6, REPEAT6(6)
#define LG8 LG7, REPEAT7(7)
#define LG9 LG8, REPEAT8(8)
#define LG10 LG9, REPEAT9(9)
#define LG11 LG10, REPEAT10(10)
#define LG12 LG11, REPEAT11(11)
#define LG13 LG12, REPEAT12(12)
#define LG14 LG13, REPEAT13(13)
#define LG15 LG14, REPEAT14(14)
#define LG16 LG15, REPEAT15(15)
#define LG17 LG16, REPEAT16(16)
#define LG18 LG17, REPEAT17(17)
#define LG19 LG18, REPEAT18(18)
#define LG20 LG19, REPEAT19(19)

const int lg2[] = { LG20 };

int main()
{
    int n;
    scanf("%d", &n);
    printf("%d\n", lg2[n]);
}