grib/
helpers.rs

1pub(crate) trait GribInt<I> {
2    fn as_grib_int(&self) -> I;
3}
4
5macro_rules! add_impl_for_ints {
6    ($(($ty_src:ty, $ty_dst:ty),)*) => ($(
7        impl GribInt<$ty_dst> for $ty_src {
8            fn as_grib_int(&self) -> $ty_dst {
9                if self.leading_zeros() == 0 {
10                    let abs = (self << 1 >> 1) as $ty_dst;
11                    -abs
12                } else {
13                    *self as $ty_dst
14                }
15            }
16        }
17    )*);
18}
19
20add_impl_for_ints! {
21    (u8, i8),
22    (u16, i16),
23    (u32, i32),
24    (u64, i64),
25}
26
27macro_rules! read_as {
28    ($ty:ty, $buf:ident, $start:expr) => {{
29        let end = $start + std::mem::size_of::<$ty>();
30        <$ty>::from_be_bytes($buf[$start..end].try_into().unwrap())
31    }};
32}
33pub(crate) use read_as;
34
35pub(crate) fn grib_int_from_bytes(bytes: &[u8]) -> i32 {
36    let len = bytes.len();
37    // Although there is logic that can be used to generalize, not so many patterns
38    // exist that generalization is necessary.
39    match len {
40        1 => i32::from(read_as!(u8, bytes, 0).as_grib_int()),
41        2 => i32::from(read_as!(u16, bytes, 0).as_grib_int()),
42        3 => {
43            let first = read_as!(u8, bytes, 0);
44            let positive = first.leading_zeros() != 0;
45            let rest = i32::from(read_as!(u16, bytes, 1));
46            let abs = i32::from(first << 1 >> 1) * 0x10000 + rest;
47            if positive { abs } else { -abs }
48        }
49        4 => read_as!(u32, bytes, 0).as_grib_int(),
50        _ => unimplemented!(),
51    }
52}
53
54#[cfg(test)]
55mod tests {
56    use super::*;
57
58    #[test]
59    fn into_grib_i8() {
60        let input: Vec<u8> = vec![0b01000000, 0b00000001, 0b10000001, 0b11000000];
61        let output: Vec<i8> = vec![64, 1, -1, -64];
62
63        let mut actual = Vec::new();
64        let mut pos = 0;
65        while pos < input.len() {
66            let val = u8::from_be_bytes(input[pos..pos + 1].try_into().unwrap());
67            pos += 1;
68            let val = val.as_grib_int();
69            actual.push(val);
70        }
71
72        assert_eq!(actual, output);
73    }
74
75    #[test]
76    fn into_grib_i16() {
77        let input: Vec<u8> = vec![
78            0b00000000, 0b01000000, 0b00000000, 0b00000001, 0b10000000, 0b00000001, 0b10000000,
79            0b01000000,
80        ];
81        let output: Vec<i16> = vec![64, 1, -1, -64];
82
83        let mut actual = Vec::new();
84        let mut pos = 0;
85        while pos < input.len() {
86            let val = u16::from_be_bytes(input[pos..pos + 2].try_into().unwrap());
87            pos += 2;
88            let val = val.as_grib_int();
89            actual.push(val);
90        }
91
92        assert_eq!(actual, output);
93    }
94
95    macro_rules! test_conversion_from_bytes_to_grib_int {
96        ($(($name:ident, $input:expr, $expected:expr),)*) => ($(
97            #[test]
98            fn $name() {
99                let bytes = $input;
100                let actual = grib_int_from_bytes(&bytes);
101                let expected = $expected;
102                assert_eq!(actual, expected)
103            }
104        )*);
105    }
106
107    test_conversion_from_bytes_to_grib_int! {
108        (
109            conversion_from_bytes_to_grib_int_for_1_byte_positive,
110            vec![0b01010101],
111            0b01010101
112        ),
113        (
114            conversion_from_bytes_to_grib_int_for_1_byte_negative,
115            vec![0b11010101],
116            -0b01010101
117        ),
118        (
119            conversion_from_bytes_to_grib_int_for_2_bytes_positive,
120            vec![0b01010101, 0b10101010],
121            0b0101_0101_1010_1010
122        ),
123        (
124            conversion_from_bytes_to_grib_int_for_2_bytes_negative,
125            vec![0b11010101, 0b10101010],
126            -0b0101_0101_1010_1010
127        ),
128        (
129            conversion_from_bytes_to_grib_int_for_3_bytes_positive,
130            vec![0b01010101, 0b10101010, 0b10101010],
131            0b0101_0101_1010_1010_1010_1010
132        ),
133        (
134            conversion_from_bytes_to_grib_int_for_3_bytes_negative,
135            vec![0b11010101, 0b10101010, 0b10101010],
136            -0b0101_0101_1010_1010_1010_1010
137        ),
138        (
139            conversion_from_bytes_to_grib_int_for_3_bytes_negative_starting_from_0x80,
140            vec![0b10000000, 0b10101010, 0b10101010],
141            -0b0000_0000_1010_1010_1010_1010
142        ),
143        (
144            conversion_from_bytes_to_grib_int_for_4_bytes_positive,
145            vec![0b01010101, 0b10101010, 0b10101010, 0b10101010],
146            0b0101_0101_1010_1010_1010_1010_1010_1010
147        ),
148        (
149            conversion_from_bytes_to_grib_int_for_4_bytes_negative,
150            vec![0b11010101, 0b10101010, 0b10101010, 0b10101010],
151            -0b0101_0101_1010_1010_1010_1010_1010_1010
152        ),
153    }
154}
grib/helpers.rs

grib/
helpers.rs
