Created
January 31, 2019 21:55
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A modulo operator in c
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#include <stdio.h> | |
#include <limits.h> | |
#include <assert.h> | |
int mod(int a, int b) { | |
int res; | |
if (b < 0) { | |
// because -INT_MIN == INT_MIN | |
if (b > INT_MIN) { | |
return -mod(-a, -b); | |
} else { | |
// b == INT_MIN | |
if (a == INT_MIN) { | |
return 0; | |
} else if (a < 0) { | |
return a; | |
} else { | |
return INT_MIN + a; | |
} | |
} | |
} | |
assert(b > 0); | |
if (a < 0) { | |
res = b - 1 - (-(a + 1)) % b; | |
} else { | |
res = a % b; | |
} | |
assert(res > INT_MIN); | |
return res; | |
} | |
int main (int argc, char** argv) | |
{ | |
printf("% i mod % i = % i\n", 2, 5, mod(2, 5)); | |
printf("% i mod % i = % i\n", -2, 5, mod(-2, 5)); | |
printf("% i mod % i = % i\n", 2, -5, mod(2, -5)); | |
printf("% i mod % i = % i\n", -2, -5, mod(-2, -5)); | |
printf("% i mod % i = % i\n", 9, 5, mod(9, 5)); | |
printf("% i mod % i = % i\n", -9, 5, mod(-9, 5)); | |
printf("% i mod % i = % i\n", 9, -5, mod(9, -5)); | |
printf("% i mod % i = % i\n", -9, -5, mod(-9, -5)); | |
printf("% i mod % i = % i\n", 10, 5, mod(10, 5)); | |
printf("% i mod % i = % i\n", -10, 5, mod(-10, 5)); | |
printf("% i mod % i = % i\n", 10, -5, mod(10, -5)); | |
printf("% i mod % i = % i\n", -10, -5, mod(-10, -5)); | |
printf("% i mod % i = % i\n", INT_MAX, 5, mod(INT_MAX, 5)); | |
printf("% i mod % i = % i\n", INT_MIN, 5, mod(INT_MIN, 5)); | |
printf("% i mod % i = % i\n", 5, INT_MAX, mod(5, INT_MAX)); | |
printf("% i mod % i = % i\n", 5, INT_MIN, mod(5, INT_MIN)); | |
printf("% i mod % i = % i\n", INT_MAX, INT_MIN, mod(INT_MAX, INT_MIN)); | |
printf("% i mod % i = % i\n", INT_MIN, INT_MAX, mod(INT_MIN, INT_MAX)); | |
printf("% i mod % i = % i\n", INT_MAX - 1, INT_MIN, mod(INT_MAX - 1, INT_MIN)); | |
printf("% i mod % i = % i\n", INT_MIN + 1, INT_MAX, mod(INT_MIN + 1, INT_MAX)); | |
printf("% i mod % i = % i\n", INT_MAX, INT_MIN + 1, mod(INT_MAX, INT_MIN + 1)); | |
printf("% i mod % i = % i\n", INT_MIN, INT_MAX - 1, mod(INT_MIN, INT_MAX - 1)); | |
return 0; | |
} |
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