vortex_sampling_compressor/compressors/
bitpacked.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
use vortex::aliases::hash_set::HashSet;
use vortex::array::PrimitiveArray;
use vortex::encoding::EncodingRef;
use vortex::stats::ArrayStatistics;
use vortex::{Array, IntoArray};
use vortex_error::{vortex_err, vortex_panic, VortexResult};
use vortex_fastlanes::{
    bitpack, count_exceptions, find_best_bit_width, find_min_patchless_bit_width, gather_patches,
    BitPackedArray, BitPackedEncoding,
};

use crate::compressors::{CompressedArray, CompressionTree, EncodingCompressor};
use crate::{constants, SamplingCompressor};

pub const BITPACK_WITH_PATCHES: BitPackedCompressor = BitPackedCompressor {
    allow_patches: true,
};
pub const BITPACK_NO_PATCHES: BitPackedCompressor = BitPackedCompressor {
    allow_patches: false,
};

#[derive(Debug)]
pub struct BitPackedCompressor {
    allow_patches: bool,
}

impl BitPackedCompressor {
    fn find_bit_width(&self, array: &PrimitiveArray) -> VortexResult<u8> {
        if self.allow_patches {
            find_best_bit_width(array)
        } else {
            find_min_patchless_bit_width(array)
        }
    }
}

impl EncodingCompressor for BitPackedCompressor {
    fn id(&self) -> &str {
        if self.allow_patches {
            "fastlanes.bitpacked"
        } else {
            "fastlanes.bitpacked_no_patches"
        }
    }

    fn cost(&self) -> u8 {
        if self.allow_patches {
            constants::BITPACKED_WITH_PATCHES_COST
        } else {
            constants::BITPACKED_NO_PATCHES_COST
        }
    }

    fn can_compress(&self, array: &Array) -> Option<&dyn EncodingCompressor> {
        // Only support primitive arrays
        let parray = PrimitiveArray::try_from(array).ok()?;

        // Only supports unsigned ints
        if !parray.ptype().is_unsigned_int() {
            return None;
        }

        let bit_width = self.find_bit_width(&parray).ok()?;

        // Check that the bit width is less than the type's bit width
        if bit_width == parray.ptype().bit_width() as u8 {
            return None;
        }

        Some(self)
    }

    fn compress<'a>(
        &'a self,
        array: &Array,
        like: Option<CompressionTree<'a>>,
        ctx: SamplingCompressor<'a>,
    ) -> VortexResult<CompressedArray<'a>> {
        let parray = array.as_primitive();
        let bit_width_freq = parray
            .statistics()
            .compute_bit_width_freq()
            .ok_or_else(|| vortex_err!(ComputeError: "missing bit width frequency"))?;

        let bit_width = self.find_bit_width(&parray)?;
        let num_exceptions = count_exceptions(bit_width, &bit_width_freq);
        if !self.allow_patches && num_exceptions > 0 {
            vortex_panic!(
                "Found {} exceptions with patchless bit width {}",
                num_exceptions,
                bit_width
            )
        }

        if bit_width == parray.ptype().bit_width() as u8 {
            // Nothing we can do
            return Ok(CompressedArray::uncompressed(array.clone()));
        }

        let validity = ctx.compress_validity(parray.validity())?;
        let packed = bitpack(&parray, bit_width)?;
        let patches = (num_exceptions > 0)
            .then(|| {
                gather_patches(&parray, bit_width, num_exceptions).map(|p| {
                    ctx.auxiliary("patches")
                        .excluding(&BITPACK_WITH_PATCHES)
                        .including(&BITPACK_NO_PATCHES)
                        .compress(&p, like.as_ref().and_then(|l| l.child(0)))
                })
            })
            .flatten()
            .transpose()?;

        Ok(CompressedArray::new(
            BitPackedArray::try_new(
                packed,
                parray.ptype(),
                validity,
                patches.as_ref().map(|p| p.array.clone()),
                bit_width,
                parray.len(),
            )?
            .into_array(),
            Some(CompressionTree::new(
                self,
                vec![patches.and_then(|p| p.path)],
            )),
        ))
    }

    fn used_encodings(&self) -> HashSet<EncodingRef> {
        HashSet::from([&BitPackedEncoding as EncodingRef])
    }
}