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abacus: bignum: add division & modulo

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Like the C language, the `%` operator is rather the remainder, such that
`(a/b)*b + (a%b) = a`.

I still call it modulo though...
This commit is contained in:
Bruno BELANYI 2021-08-21 01:51:33 +02:00
parent 7cd0664e60
commit 4e3d53ecd4
3 changed files with 151 additions and 0 deletions
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61
tests/unit/bignum.cc
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@ -206,3 +206,64 @@ TEST(BigNum, multiplication_mixed_signs) {
EXPECT_EQ(minus_two * two, minus_four);
EXPECT_EQ(minus_two * minus_two, four);
}
TEST(BigNum, division) {
auto const zero = BigNum(0);
auto const one = BigNum(1);
auto const two = BigNum(2);
EXPECT_EQ(one / one, one);
EXPECT_EQ(one / two, zero);
EXPECT_EQ(two / one, two);
}
TEST(BigNum, division_negative) {
auto const zero = BigNum(0);
auto const one = BigNum(1);
auto const minus_one = BigNum(-1);
auto const two = BigNum(2);
auto const minus_two = BigNum(-2);
EXPECT_EQ(one / minus_one, minus_one);
EXPECT_EQ(minus_one / one, minus_one);
EXPECT_EQ(minus_one / minus_one, one);
EXPECT_EQ(two / minus_two, minus_one);
EXPECT_EQ(minus_two / two, minus_one);
EXPECT_EQ(minus_two / minus_two, one);
EXPECT_EQ(one / minus_two, zero);
EXPECT_EQ(minus_one / two, zero);
EXPECT_EQ(one / minus_two, zero);
EXPECT_EQ(minus_one / minus_two, zero);
EXPECT_EQ(two / minus_one, minus_two);
EXPECT_EQ(minus_two / minus_one, two);
EXPECT_EQ(minus_two / one, minus_two);
}
TEST(BigNum, division_truncate) {
auto const one = BigNum(1);
auto const minus_one = BigNum(-1);
auto const three = BigNum(3);
auto const minus_three = BigNum(-3);
auto const five = BigNum(5);
auto const minus_five = BigNum(-5);
EXPECT_EQ(five / three, one);
EXPECT_EQ(five / minus_three, minus_one);
EXPECT_EQ(minus_five / three, minus_one);
EXPECT_EQ(minus_five / minus_three, one);
}
TEST(BigNum, div_mod_identity) {
auto const three = BigNum(3);
auto const minus_three = BigNum(-3);
auto const five = BigNum(5);
auto const minus_five = BigNum(-5);
EXPECT_EQ((five / three) * three + (five % three), five);
EXPECT_EQ((five / minus_three) * minus_three + (five % minus_three), five);
EXPECT_EQ((minus_five / three) * three + (minus_five % three), minus_five);
EXPECT_EQ((minus_five / minus_three) * minus_three
+ (minus_five % minus_three),
minus_five);
}