pyra_margin/
math.rs

1/// Checked ceiling division for integer types.
2pub trait CheckedDivCeil {
3    fn checked_div_ceil(self, rhs: Self) -> Option<Self>
4    where
5        Self: Sized;
6}
7
8impl CheckedDivCeil for u128 {
9    fn checked_div_ceil(self, divisor: u128) -> Option<u128> {
10        if divisor == 0 {
11            return None;
12        }
13        let quotient = self.checked_div(divisor)?;
14        let product = quotient.checked_mul(divisor)?;
15        let remainder = self.checked_sub(product)?;
16        if remainder == 0 {
17            Some(quotient)
18        } else {
19            quotient.checked_add(1)
20        }
21    }
22}
23
24impl CheckedDivCeil for i128 {
25    fn checked_div_ceil(self, divisor: i128) -> Option<i128> {
26        if divisor == 0 {
27            return None;
28        }
29        let quotient = self.checked_div(divisor)?;
30        let quotient_times_divisor = quotient.checked_mul(divisor)?;
31        let remainder = self.checked_sub(quotient_times_divisor)?;
32        if remainder == 0 {
33            return Some(quotient);
34        }
35        // Round up only when both operands have the same sign
36        let same_sign = (self > 0 && divisor > 0) || (self < 0 && divisor < 0);
37        if same_sign {
38            quotient.checked_add(1)
39        } else {
40            Some(quotient)
41        }
42    }
43}
44
45impl CheckedDivCeil for i64 {
46    fn checked_div_ceil(self, divisor: i64) -> Option<i64> {
47        if divisor == 0 {
48            return None;
49        }
50        let quotient = self.checked_div(divisor)?;
51        let quotient_times_divisor = quotient.checked_mul(divisor)?;
52        let remainder = self.checked_sub(quotient_times_divisor)?;
53        if remainder == 0 {
54            return Some(quotient);
55        }
56        let same_sign = (self > 0 && divisor > 0) || (self < 0 && divisor < 0);
57        if same_sign {
58            quotient.checked_add(1)
59        } else {
60            Some(quotient)
61        }
62    }
63}
64
65#[cfg(test)]
66#[allow(
67    clippy::unwrap_used,
68    clippy::expect_used,
69    clippy::panic,
70    clippy::arithmetic_side_effects
71)]
72mod tests {
73    use super::*;
74
75    #[test]
76    fn u128_div_ceil_exact() {
77        assert_eq!(10u128.checked_div_ceil(5), Some(2));
78    }
79
80    #[test]
81    fn u128_div_ceil_rounds_up() {
82        assert_eq!(11u128.checked_div_ceil(5), Some(3));
83    }
84
85    #[test]
86    fn u128_div_ceil_zero_divisor() {
87        assert_eq!(10u128.checked_div_ceil(0), None);
88    }
89
90    #[test]
91    fn i128_div_ceil_positive() {
92        assert_eq!(11i128.checked_div_ceil(5), Some(3));
93    }
94
95    #[test]
96    fn i128_div_ceil_negative_no_roundup() {
97        // -11 / 5 = -2 remainder -1; different signs, no round up
98        assert_eq!((-11i128).checked_div_ceil(5), Some(-2));
99    }
100
101    #[test]
102    fn i128_div_ceil_both_negative_rounds_up() {
103        // -11 / -5 = 2 remainder -1; same signs, round up
104        assert_eq!((-11i128).checked_div_ceil(-5), Some(3));
105    }
106
107    #[test]
108    fn i64_div_ceil_exact() {
109        assert_eq!(10i64.checked_div_ceil(5), Some(2));
110    }
111
112    #[test]
113    fn i64_div_ceil_rounds_up() {
114        assert_eq!(11i64.checked_div_ceil(5), Some(3));
115    }
116}
117
118#[cfg(test)]
119#[allow(
120    clippy::unwrap_used,
121    clippy::expect_used,
122    clippy::panic,
123    clippy::arithmetic_side_effects
124)]
125mod proptests {
126    use super::*;
127    use proptest::prelude::*;
128
129    proptest! {
130        #[test]
131        fn u128_div_ceil_never_panics(a: u128, b: u128) {
132            let _ = a.checked_div_ceil(b);
133        }
134
135        #[test]
136        fn u128_div_ceil_correct(a in 0u128..=u128::MAX / 2, b in 1u128..=1_000_000_000) {
137            let result = a.checked_div_ceil(b).unwrap();
138            // result >= a/b (ceiling property)
139            let floor = a / b;
140            let remainder = a % b;
141            if remainder == 0 {
142                prop_assert_eq!(result, floor);
143            } else {
144                prop_assert_eq!(result, floor + 1);
145            }
146        }
147
148        #[test]
149        fn i128_div_ceil_never_panics(a: i64, b: i64) {
150            let _ = (a as i128).checked_div_ceil(b as i128);
151        }
152
153        #[test]
154        fn i128_div_ceil_rounds_toward_positive_infinity_for_same_sign(
155            a in 1i128..=1_000_000_000_000,
156            b in 1i128..=1_000_000_000,
157        ) {
158            let result = a.checked_div_ceil(b).unwrap();
159            // For positive/positive: result * b >= a
160            prop_assert!(result * b >= a);
161            // But (result - 1) * b < a (tightest ceiling)
162            prop_assert!((result - 1) * b < a);
163        }
164    }
165}
pyra_margin/math.rs

pyra_margin/
math.rs
