fixed_bigint/fixeduint/
div_ceil_impl.rs

1// Copyright 2021 Google LLC
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//      http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15//! Ceiling division for FixedUInt.
16
17use super::{const_div, const_is_zero, FixedUInt, MachineWord};
18use crate::const_numtraits::{ConstCheckedAdd, ConstDivCeil, ConstOne};
19use crate::machineword::ConstMachineWord;
20use crate::personality::Nct;
21
22c0nst::c0nst! {
23    impl<T: [c0nst] ConstMachineWord + MachineWord, const N: usize> c0nst ConstDivCeil for FixedUInt<T, N, Nct> {
24        fn div_ceil(self, rhs: Self) -> Self {
25            match self.checked_div_ceil(rhs) {
26                Some(v) => v,
27                None => panic!("div_ceil: division by zero or overflow"),
28            }
29        }
30
31        fn checked_div_ceil(self, rhs: Self) -> Option<Self> {
32            if const_is_zero(&rhs.array) {
33                return None;
34            }
35            // Use const_div which computes both quotient and remainder in one pass
36            let mut quotient = self.array;
37            let remainder = const_div(&mut quotient, &rhs.array);
38            if const_is_zero(&remainder) {
39                Some(Self::from_array(quotient))
40            } else {
41                // Use checked_add to return None on overflow
42                ConstCheckedAdd::checked_add(&Self::from_array(quotient), &Self::one())
43            }
44        }
45    }
46}
47
48#[cfg(test)]
49mod tests {
50    use super::*;
51
52    #[test]
53    fn test_div_ceil() {
54        type U16 = FixedUInt<u8, 2>;
55
56        // Exact division
57        assert_eq!(
58            ConstDivCeil::div_ceil(U16::from(10u8), U16::from(5u8)),
59            U16::from(2u8)
60        );
61        assert_eq!(
62            ConstDivCeil::div_ceil(U16::from(10u8), U16::from(2u8)),
63            U16::from(5u8)
64        );
65
66        // Rounds up
67        assert_eq!(
68            ConstDivCeil::div_ceil(U16::from(10u8), U16::from(3u8)),
69            U16::from(4u8)
70        ); // 10/3 = 3.33... -> 4
71        assert_eq!(
72            ConstDivCeil::div_ceil(U16::from(11u8), U16::from(3u8)),
73            U16::from(4u8)
74        ); // 11/3 = 3.66... -> 4
75        assert_eq!(
76            ConstDivCeil::div_ceil(U16::from(12u8), U16::from(3u8)),
77            U16::from(4u8)
78        ); // 12/3 = 4 exact
79
80        // Edge cases
81        assert_eq!(
82            ConstDivCeil::div_ceil(U16::from(0u8), U16::from(5u8)),
83            U16::from(0u8)
84        );
85        assert_eq!(
86            ConstDivCeil::div_ceil(U16::from(1u8), U16::from(5u8)),
87            U16::from(1u8)
88        ); // 1/5 = 0.2 -> 1
89        assert_eq!(
90            ConstDivCeil::div_ceil(U16::from(1u8), U16::from(1u8)),
91            U16::from(1u8)
92        );
93    }
94
95    #[test]
96    fn test_checked_div_ceil() {
97        type U16 = FixedUInt<u8, 2>;
98
99        assert_eq!(
100            ConstDivCeil::checked_div_ceil(U16::from(10u8), U16::from(3u8)),
101            Some(U16::from(4u8))
102        );
103
104        // Division by zero
105        assert_eq!(
106            ConstDivCeil::checked_div_ceil(U16::from(10u8), U16::from(0u8)),
107            None
108        );
109
110        // Edge case: MAX / 2 = 32767 remainder 1, ceil = 32768
111        assert_eq!(
112            ConstDivCeil::checked_div_ceil(U16::from(65535u16), U16::from(2u16)),
113            Some(U16::from(32768u16))
114        );
115
116        // Edge case: MAX / 1 = MAX exactly (no remainder, no +1 needed)
117        assert_eq!(
118            ConstDivCeil::checked_div_ceil(U16::from(65535u16), U16::from(1u16)),
119            Some(U16::from(65535u16))
120        );
121    }
122
123    c0nst::c0nst! {
124        pub c0nst fn const_div_ceil<T: [c0nst] ConstMachineWord + MachineWord, const N: usize>(
125            a: FixedUInt<T, N, Nct>,
126            b: FixedUInt<T, N, Nct>,
127        ) -> FixedUInt<T, N, Nct> {
128            ConstDivCeil::div_ceil(a, b)
129        }
130    }
131
132    #[test]
133    fn test_const_div_ceil() {
134        type U16 = FixedUInt<u8, 2>;
135
136        assert_eq!(
137            const_div_ceil(U16::from(10u8), U16::from(3u8)),
138            U16::from(4u8)
139        );
140
141        #[cfg(feature = "nightly")]
142        {
143            const TEN: U16 = FixedUInt::from_array([10, 0]);
144            const THREE: U16 = FixedUInt::from_array([3, 0]);
145            const RESULT: U16 = const_div_ceil(TEN, THREE);
146            assert_eq!(RESULT, FixedUInt::from_array([4, 0]));
147        }
148    }
149}
fixed_bigint/fixeduint/div_ceil_impl.rs

fixed_bigint/fixeduint/
div_ceil_impl.rs
