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Safe signed multiplication test suite
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <stdint.h> | |
#include <limits.h> | |
// Multiplies two 64-bit signed ints if possible. | |
// Returns 0 on success, and puts the product of x and y into the result. | |
// Returns 1 if there was an overflow. | |
int int64_mult(int64_t x, int64_t y, int64_t * result) | |
{ | |
*result = 0; | |
if (x > 0 && y > 0 && x > INT64_MAX / y) return 1; | |
if (x < 0 && y > 0 && x < INT64_MIN / y) return 1; | |
if (x > 0 && y < 0 && y < INT64_MIN / x) return 1; | |
if (x < 0 && y < 0 && (x <= INT64_MIN || y <= INT64_MIN || -x > INT64_MAX / -y)) | |
return 1; | |
*result = x * y; | |
return 0; | |
} | |
void test_int64_mult_success(int64_t x, int64_t y, int64_t expected) | |
{ | |
int64_t result; | |
// x * y | |
if (int64_mult(x, y, &result)) | |
{ | |
fprintf(stderr, "unexpected overflow: %lld %lld\n", x, y); | |
} | |
if (result != expected) | |
{ | |
fprintf(stderr, "wrong result: %lld %lld %lld %lld\n", x, y, expected, result); | |
} | |
// y * x should be the same | |
if (int64_mult(y, x, &result)) | |
{ | |
fprintf(stderr, "unexpected overflow: %lld %lld\n", y, x); | |
} | |
if (result != expected) | |
{ | |
fprintf(stderr, "wrong result: %lld %lld %lld %lld\n", y, x, expected, result); | |
} | |
} | |
void test_int64_mult_error(int64_t x, int64_t y) | |
{ | |
int64_t result; | |
// x * y | |
if (int64_mult(x, y, &result) == 0) | |
{ | |
fprintf(stderr, "unexpected success: %lld %lld\n", x, y); | |
} | |
// y * x shoul be the same | |
if (int64_mult(y, x, &result) == 0) | |
{ | |
fprintf(stderr, "unexpected success: %lld %lld\n", y, x); | |
} | |
} | |
int main() | |
{ | |
// min, min | |
test_int64_mult_error(INT64_MIN, INT64_MIN); | |
// min, min/100 | |
test_int64_mult_error(INT64_MIN, INT64_MIN / 100); | |
// min, 0 | |
test_int64_mult_error(INT64_MIN, -2); | |
test_int64_mult_error(INT64_MIN, -1); | |
test_int64_mult_success(INT64_MIN, 0, 0); | |
test_int64_mult_success(INT64_MIN, 1, INT64_MIN); | |
test_int64_mult_error(INT64_MIN, 2); | |
// min, max/100 | |
test_int64_mult_error(INT64_MIN, INT64_MAX / 100); | |
// min, max | |
test_int64_mult_error(INT64_MIN, INT64_MAX); | |
// min/100, min/100 | |
test_int64_mult_error(INT64_MIN / 100, INT64_MIN / 100); | |
// min/100, 0 | |
test_int64_mult_error(INT64_MIN / 100, -101); | |
test_int64_mult_success(INT64_MIN / 100, -100, 0x7ffffffffffffff8); | |
test_int64_mult_success(INT64_MIN / 100, -99, 0x7eb851eb851eb84a); | |
test_int64_mult_success(INT64_MIN / 100, 0, 0); | |
test_int64_mult_success(INT64_MIN / 100, 100, -0x7ffffffffffffff8); | |
test_int64_mult_error(INT64_MIN / 100, 101); | |
// min/100, max/100 | |
test_int64_mult_error(INT64_MIN / 100, INT64_MAX / 100); | |
// min/100, max | |
test_int64_mult_error(INT64_MIN / 100, INT64_MAX); | |
// 0, 0 | |
test_int64_mult_success(0, 0, 0); | |
test_int64_mult_success(0, 1, 0); | |
test_int64_mult_success(1, 1, 1); | |
test_int64_mult_success(1, 3, 3); | |
test_int64_mult_success(3, 3, 9); | |
// 0, max/100 | |
test_int64_mult_error(INT64_MAX / 100, -101); | |
test_int64_mult_success(INT64_MAX / 100, -100, -0x7ffffffffffffff8); | |
test_int64_mult_success(INT64_MAX / 100, -99, -0x7eb851eb851eb84a); | |
test_int64_mult_success(INT64_MAX / 100, 0, 0); | |
test_int64_mult_success(INT64_MAX / 100, 100, 0x7ffffffffffffff8); | |
test_int64_mult_error(INT64_MAX / 100, 101); | |
// 0, max | |
test_int64_mult_error(-2, INT64_MAX); | |
test_int64_mult_success(-1, INT64_MAX, -INT64_MAX); | |
test_int64_mult_success(0, INT64_MAX, 0); | |
test_int64_mult_success(1, INT64_MAX, INT64_MAX); | |
test_int64_mult_error(2, INT64_MAX); | |
// max/100, max | |
test_int64_mult_error(INT64_MAX / 100, INT64_MAX); | |
} |
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