toolshed 0.8.1

Arena allocator and a handful of useful data structures
Documentation 
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const A__: u16 = 0;
const A00: u16 = 1;
const A01: u16 = 1 << 1;
const A02: u16 = 1 << 2;
const A03: u16 = 1 << 3;
const A04: u16 = 1 << 4;
const A05: u16 = 1 << 5;
const A06: u16 = 1 << 6;
const A07: u16 = 1 << 7;
const A08: u16 = 1 << 8;
const A09: u16 = 1 << 9;
const A10: u16 = 1 << 10;
const A11: u16 = 1 << 11;
const A12: u16 = 1 << 12;
const A13: u16 = 1 << 13;
const A14: u16 = 1 << 14;
const A15: u16 = 1 << 15;

const B__: u32 = 0;
const B00: u32 = 1 << 16;
const B01: u32 = 1 << 17;
const B02: u32 = 1 << 18;
const B03: u32 = 1 << 19;
const B04: u32 = 1 << 20;
const B05: u32 = 1 << 21;
const B06: u32 = 1 << 22;
const B07: u32 = 1 << 23;
const B08: u32 = 1 << 24;
const B09: u32 = 1 << 25;
const B10: u32 = 1 << 26;
const B11: u32 = 1 << 27;
const B12: u32 = 1 << 28;
const B13: u32 = 1 << 29;
const B14: u32 = 1 << 30;
const B15: u32 = 1 << 31;

const C__: u64 = 0;
const C00: u64 = 1 << 32;
const C01: u64 = 1 << 33;
const C02: u64 = 1 << 34;
const C03: u64 = 1 << 35;
const C04: u64 = 1 << 36;
const C05: u64 = 1 << 37;
const C06: u64 = 1 << 38;
const C07: u64 = 1 << 39;
const C08: u64 = 1 << 40;
const C09: u64 = 1 << 41;
const C10: u64 = 1 << 42;
const C11: u64 = 1 << 43;
const C12: u64 = 1 << 44;
const C13: u64 = 1 << 45;
const C14: u64 = 1 << 46;
const C15: u64 = 1 << 47;

static BYTE_MASKS_A: [u16; 256] = [
//    0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F  //
    A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, // 0
    A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, // 1
    A__, A__, A__, A__, A01, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, A__, // 2
    A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A__, A__, A__, A__, A__, A__, // 3
    A__, A12, A13, A14, A15, A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, // 4
    A11, A12, A13, A14, A15, A00, A01, A02, A03, A04, A05, A__, A__, A__, A__, A00, // 5
    A__, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, A00, A01, A02, A03, A04, // 6
    A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, A__, A__, A__, A__, A__, // 7
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // 8
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // 9
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // A
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // B
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // C
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // D
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // E
    A00, A01, A02, A03, A04, A05, A06, A07, A08, A09, A10, A11, A12, A13, A14, A15, // F
];

static BYTE_MASKS_B: [u32; 256] = [
//    0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F  //
    B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, // 0
    B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, // 1
    B__, B__, B__, B__, B01, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, B__, // 2
    B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B__, B__, B__, B__, B__, B__, // 3
    B__, B12, B13, B14, B15, B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, // 4
    B11, B12, B13, B14, B15, B00, B01, B02, B03, B04, B05, B__, B__, B__, B__, B00, // 5
    B__, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, B00, B01, B02, B03, B04, // 6
    B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, B__, B__, B__, B__, B__, // 7
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // 8
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // 9
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // A
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // B
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // C
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // D
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // E
    B00, B01, B02, B03, B04, B05, B06, B07, B08, B09, B10, B11, B12, B13, B14, B15, // F
];

static BYTE_MASKS_C: [u64; 256] = [
//    0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F  //
    C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, // 0
    C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, // 1
    C__, C__, C__, C__, C01, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, C__, // 2
    C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C__, C__, C__, C__, C__, C__, // 3
    C__, C12, C13, C14, C15, C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, // 4
    C11, C12, C13, C14, C15, C00, C01, C02, C03, C04, C05, C__, C__, C__, C__, C00, // 5
    C__, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, C00, C01, C02, C03, C04, // 6
    C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, C__, C__, C__, C__, C__, // 7
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // 8
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // 9
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // A
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // B
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // C
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // D
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // E
    C00, C01, C02, C03, C04, C05, C06, C07, C08, C09, C10, C11, C12, C13, C14, C15, // F
];

/// Calculate a bloom filter for `T`. This function is very fast and works as a constant
/// speed regardless of the length of bytes, ~1ns on modern laptop.
#[inline]
pub fn bloom<T: AsRef<[u8]>>(val: T) -> u64 {
    let s = val.as_ref();

    match s.len() {
        0 => 0x0001000000000000,

        1 => 0x0002000000000000
           | BYTE_MASKS_A[s[0] as usize] as u64,

        2 => 0x0004000000000000
           | BYTE_MASKS_A[s[0] as usize] as u64
           | BYTE_MASKS_B[s[1] as usize] as u64,

        n => 0x0001000000000000 << n % 16
           | BYTE_MASKS_C[s[2] as usize]
           | BYTE_MASKS_B[s[1] as usize] as u64
           | BYTE_MASKS_A[s[0] as usize] as u64
    }
}


#[cfg(test)]
mod test {
    use super::*;

    fn is_match(filter: u64, bloom: u64) -> bool {
        filter & bloom == bloom
    }

    #[test]
    fn produces_correct_number_of_bits() {
        assert_eq!(bloom("").count_ones(), 1);      // just length
        assert_eq!(bloom("a").count_ones(), 2);     // length + 1 byte
        assert_eq!(bloom("ab").count_ones(), 3);    // length + 2 bytes
        assert_eq!(bloom("abc").count_ones(), 4);   // length + 3 bytes
        assert_eq!(bloom("abcd").count_ones(), 4);  // length + 3 bytes (ignore rest)
        assert_eq!(bloom("abcde").count_ones(), 4);
        assert_eq!(bloom("abcdef").count_ones(), 4);
        assert_eq!(bloom("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ").count_ones(), 4);

        assert_eq!(bloom("").count_ones(), 1);
        assert_eq!(bloom("_").count_ones(), 2);
        assert_eq!(bloom("_$").count_ones(), 3);
        assert_eq!(bloom("_$0").count_ones(), 4);
        assert_eq!(bloom("123").count_ones(), 4);
        assert_eq!(bloom("456").count_ones(), 4);
        assert_eq!(bloom("789").count_ones(), 4);

        // special characters (other than `$` and `_`) are void, not to add garbage to the filter
        assert_eq!(bloom("").count_ones(), 1);
        assert_eq!(bloom("{").count_ones(), 1);
        assert_eq!(bloom("{}").count_ones(), 1);
        assert_eq!(bloom("{}[").count_ones(), 1);
        assert_eq!(bloom("{}[]").count_ones(), 1);
    }

    #[test]
    fn does_not_conflict_on_different_lengths() {
        let filter = bloom("abcd") | bloom("ab");

        // For visibility :)
        const __: bool = false;

        assert_eq!(is_match(filter, bloom("")), __);
        assert_eq!(is_match(filter, bloom("a")), __);
        assert_eq!(is_match(filter, bloom("ab")), true);
        assert_eq!(is_match(filter, bloom("abc")), __);
        assert_eq!(is_match(filter, bloom("abcd")), true);
        assert_eq!(is_match(filter, bloom("abcde")), __);
        assert_eq!(is_match(filter, bloom("abcdef")), __);
    }

    #[test]
    fn does_not_conflict_on_letter_casing() {
        let filter = bloom("abc") | bloom("def");

        assert_eq!(is_match(filter, bloom("abc")), true);
        assert_eq!(is_match(filter, bloom("def")), true);
        assert_eq!(is_match(filter, bloom("ABC")), false);
        assert_eq!(is_match(filter, bloom("DEF")), false);
    }

    #[test]
    fn has_low_enough_conflict_rate() {
        let filter = bloom("alloc_bytes") | bloom("alloc") | bloom("Cell") | bloom("String") | bloom("yetAnother");
        let mut matches = 0;

        assert!(is_match(filter, bloom("alloc_bytes")));
        assert!(is_match(filter, bloom("alloc")));
        assert!(is_match(filter, bloom("Cell")));
        assert!(is_match(filter, bloom("String")));
        assert!(is_match(filter, bloom("yetAnother")));

        static WORDS: &[&str] = &[
            "ARENA_BLOCK", "Arena", "Cell", "Self", "String", "T", "Vec", "_unchecked", "a",
            "alignment", "alloc", "alloc_bytes", "alloc_str", "alloc_str_zero_end", "alloc_string",
            "as", "as_bytes", "as_mut_ptr", "as_ptr", "block", "cap", "cell", "const",
            "copy_nonoverlapping", "else", "extend_from_slice", "fn", "from_raw_parts", "from_utf",
            "get", "grow", "if", "impl", "inline", "into", "into_bytes", "isize", "len",
            "len_with_zero", "let", "mem", "mut", "new", "offset", "ptr", "pub", "push",
            "replace", "return", "self", "set", "size_of", "slice", "std", "store", "str",
            "struct", "temp", "u", "unsafe", "use", "usize", "val", "vec", "with_capacity"
        ];

        for word in WORDS.iter() {

            if is_match(filter, bloom(word)) {
                matches += 1;
            }
        }

        // `yetAnother` is not in the WORDS, however there is a conflict with `Self`, which is ok!
        assert_eq!(matches, 5);
    }
}