    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
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305
    306
    307
    308
    309
    310
    311
    312
    313
    314
    315
    316
    317
    318
    319
    320
    321
    322
    323
    324
    325
    326
    327
    328
    329
    330
    331
    332
    333
    334
    335
    336
    337
    338
    339
    340
    341
    342
    343
    344
    345
    346
    347
    348
    349
    350
    351
    352
    353
    354
    355
    356
    357
    358
    359
    360
    361
    362
    363
    364
    365
    366
    367
    368
    369
    370
    371
    372
    373
    374
    375
    376
    377
    378
    379
    380
    381
    382
    383
    384
    385
    386
    387
    388
    389
    390
    391
    392

    use crate::convert::*;
    use crate::operations::folded_multiply;
    use crate::operations::read_small;
    use crate::random_state::PI;
    use crate::RandomState;
    use core::hash::Hasher;

    ///This constant come from Kunth's prng (Empirically it works better than those from splitmix32).
    pub(crate) const MULTIPLE: u64 = 6364136223846793005;
    const ROT: u32 = 23; //17

    /// A `Hasher` for hashing an arbitrary stream of bytes.
    ///
    /// Instances of [`AHasher`] represent state that is updated while hashing data.
    ///
    /// Each method updates the internal state based on the new data provided. Once
    /// all of the data has been provided, the resulting hash can be obtained by calling
    /// `finish()`
    ///
    /// [Clone] is also provided in case you wish to calculate hashes for two different items that
    /// start with the same data.
    ///
    #[derive(Debug, Clone)]
    pub struct AHasher {
        buffer: u64,
        pad: u64,
        extra_keys: [u64; 2],
    }

    impl AHasher {
        /// Creates a new hasher keyed to the provided key.
        #[inline]
        #[allow(dead_code)] // Is not called if non-fallback hash is used.
        pub fn new_with_keys(key1: u128, key2: u128) -> AHasher {
            let pi: [u128; 2] = PI.convert();
            let key1: [u64; 2] = (key1 ^ pi[0]).convert();
            let key2: [u64; 2] = (key2 ^ pi[1]).convert();
            AHasher {
                buffer: key1[0],
                pad: key1[1],
                extra_keys: key2,
            }
        }

        #[allow(unused)] // False positive
        pub(crate) fn test_with_keys(key1: u128, key2: u128) -> Self {
            let key1: [u64; 2] = key1.convert();
            let key2: [u64; 2] = key2.convert();
            Self {
                buffer: key1[0],
                pad: key1[1],
                extra_keys: key2,
            }
        }

        #[inline]
        #[allow(dead_code)] // Is not called if non-fallback hash is used.
        pub(crate) fn from_random_state(rand_state: &RandomState) -> AHasher {
            AHasher {
                buffer: rand_state.k0,
                pad: rand_state.k1,
                extra_keys: [rand_state.k2, rand_state.k3],
            }
        }

        /// This update function has the goal of updating the buffer with a single multiply
        /// FxHash does this but is vulnerable to attack. To avoid this input needs to be masked to with an
        /// unpredictable value. Other hashes such as murmurhash have taken this approach but were found vulnerable
        /// to attack. The attack was based on the idea of reversing the pre-mixing (Which is necessarily
        /// reversible otherwise bits would be lost) then placing a difference in the highest bit before the
        /// multiply used to mix the data. Because a multiply can never affect the bits to the right of it, a
        /// subsequent update that also differed in this bit could result in a predictable collision.
        ///
        /// This version avoids this vulnerability while still only using a single multiply. It takes advantage
        /// of the fact that when a 64 bit multiply is performed the upper 64 bits are usually computed and thrown
        /// away. Instead it creates two 128 bit values where the upper 64 bits are zeros and multiplies them.
        /// (The compiler is smart enough to turn this into a 64 bit multiplication in the assembly)
        /// Then the upper bits are xored with the lower bits to produce a single 64 bit result.
        ///
        /// To understand why this is a good scrambling function it helps to understand multiply-with-carry PRNGs:
        /// https://en.wikipedia.org/wiki/Multiply-with-carry_pseudorandom_number_generator
        /// If the multiple is chosen well, this creates a long period, decent quality PRNG.
        /// Notice that this function is equivalent to this except the `buffer`/`state` is being xored with each
        /// new block of data. In the event that data is all zeros, it is exactly equivalent to a MWC PRNG.
        ///
        /// This is impervious to attack because every bit buffer at the end is dependent on every bit in
        /// `new_data ^ buffer`. For example suppose two inputs differed in only the 5th bit. Then when the
        /// multiplication is performed the `result` will differ in bits 5-69. More specifically it will differ by
        /// 2^5 * MULTIPLE. However in the next step bits 65-128 are turned into a separate 64 bit value. So the
        /// differing bits will be in the lower 6 bits of this value. The two intermediate values that differ in
        /// bits 5-63 and in bits 0-5 respectively get added together. Producing an output that differs in every
        /// bit. The addition carries in the multiplication and at the end additionally mean that the even if an
        /// attacker somehow knew part of (but not all) the contents of the buffer before hand,
        /// they would not be able to predict any of the bits in the buffer at the end.
        #[inline(always)]
        #[cfg(feature = "folded_multiply")]
        fn update(&mut self, new_data: u64) {
            self.buffer = folded_multiply(new_data ^ self.buffer, MULTIPLE);
        }

        #[inline(always)]
        #[cfg(not(feature = "folded_multiply"))]
        fn update(&mut self, new_data: u64) {
            let d1 = (new_data ^ self.buffer).wrapping_mul(MULTIPLE);
            self.pad = (self.pad ^ d1).rotate_left(8).wrapping_mul(MULTIPLE);
            self.buffer = (self.buffer ^ self.pad).rotate_left(24);
        }

        /// Similar to the above this function performs an update using a "folded multiply".
        /// However it takes in 128 bits of data instead of 64. Both halves must be masked.
        ///
        /// This makes it impossible for an attacker to place a single bit difference between
        /// two blocks so as to cancel each other.
        ///
        /// However this is not sufficient. to prevent (a,b) from hashing the same as (b,a) the buffer itself must
        /// be updated between calls in a way that does not commute. To achieve this XOR and Rotate are used.
        /// Add followed by xor is not the same as xor followed by add, and rotate ensures that the same out bits
        /// can't be changed by the same set of input bits. To cancel this sequence with subsequent input would require
        /// knowing the keys.
        #[inline(always)]
        #[cfg(feature = "folded_multiply")]
        fn large_update(&mut self, new_data: u128) {
            let block: [u64; 2] = new_data.convert();
            let combined = folded_multiply(block[0] ^ self.extra_keys[0], block[1] ^ self.extra_keys[1]);
            self.buffer = (self.buffer.wrapping_add(self.pad) ^ combined).rotate_left(ROT);
        }

        #[inline(always)]
        #[cfg(not(feature = "folded_multiply"))]
        fn large_update(&mut self, new_data: u128) {
            let block: [u64; 2] = new_data.convert();
            self.update(block[0] ^ self.extra_keys[0]);
            self.update(block[1] ^ self.extra_keys[1]);
        }

        #[inline]
        #[cfg(feature = "specialize")]
        fn short_finish(&self) -> u64 {
            self.buffer.wrapping_add(self.pad)
        }
    }

    /// Provides [Hasher] methods to hash all of the primitive types.
    ///
    /// [Hasher]: core::hash::Hasher
    impl Hasher for AHasher {
        #[inline]
        fn write_u8(&mut self, i: u8) {
            self.update(i as u64);
        }

        #[inline]
        fn write_u16(&mut self, i: u16) {
            self.update(i as u64);
        }

        #[inline]
        fn write_u32(&mut self, i: u32) {
            self.update(i as u64);
        }

        #[inline]
        fn write_u64(&mut self, i: u64) {
            self.update(i as u64);
        }

        #[inline]
        fn write_u128(&mut self, i: u128) {
            self.large_update(i);
        }

        #[inline]
        #[cfg(any(target_pointer_width = "64", target_pointer_width = "32", target_pointer_width = "16"))]
        fn write_usize(&mut self, i: usize) {
            self.write_u64(i as u64);
        }

        #[inline]
        #[cfg(target_pointer_width = "128")]
        fn write_usize(&mut self, i: usize) {
            self.write_u128(i as u128);
        }

        #[inline]
        #[allow(clippy::collapsible_if)]
        fn write(&mut self, input: &[u8]) {
            let mut data = input;
            let length = data.len() as u64;
            //Needs to be an add rather than an xor because otherwise it could be canceled with carefully formed input.
            self.buffer = self.buffer.wrapping_add(length).wrapping_mul(MULTIPLE);
            //A 'binary search' on sizes reduces the number of comparisons.
            if data.len() > 8 {
                if data.len() > 16 {
                    let tail = data.read_last_u128();
                    self.large_update(tail);
                    while data.len() > 16 {
                        let (block, rest) = data.read_u128();
                        self.large_update(block);
                        data = rest;
                    }
                } else {
                    self.large_update([data.read_u64().0, data.read_last_u64()].convert());
                }
            } else {
                let value = read_small(data);
                self.large_update(value.convert());
            }
        }

        #[inline]
        #[cfg(feature = "folded_multiply")]
        fn finish(&self) -> u64 {
            let rot = (self.buffer & 63) as u32;
            folded_multiply(self.buffer, self.pad).rotate_left(rot)
        }

        #[inline]
        #[cfg(not(feature = "folded_multiply"))]
        fn finish(&self) -> u64 {
            let rot = (self.buffer & 63) as u32;
            (self.buffer.wrapping_mul(MULTIPLE) ^ self.pad).rotate_left(rot)
        }
    }

    #[cfg(feature = "specialize")]
    pub(crate) struct AHasherU64 {
        pub(crate) buffer: u64,
        pub(crate) pad: u64,
    }

    /// A specialized hasher for only primitives under 64 bits.
    #[cfg(feature = "specialize")]
    impl Hasher for AHasherU64 {
        #[inline]
        fn finish(&self) -> u64 {
            let rot = (self.pad & 63) as u32;
            self.buffer.rotate_left(rot)
        }

        #[inline]
        fn write(&mut self, _bytes: &[u8]) {
            unreachable!("Specialized hasher was called with a different type of object")
        }

        #[inline]
        fn write_u8(&mut self, i: u8) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u16(&mut self, i: u16) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u32(&mut self, i: u32) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u64(&mut self, i: u64) {
            self.buffer = folded_multiply(i ^ self.buffer, MULTIPLE);
        }

        #[inline]
        fn write_u128(&mut self, _i: u128) {
            unreachable!("Specialized hasher was called with a different type of object")
        }

        #[inline]
        fn write_usize(&mut self, _i: usize) {
            unreachable!("Specialized hasher was called with a different type of object")
        }
    }

    #[cfg(feature = "specialize")]
    pub(crate) struct AHasherFixed(pub AHasher);

    /// A specialized hasher for fixed size primitives larger than 64 bits.
    #[cfg(feature = "specialize")]
    impl Hasher for AHasherFixed {
        #[inline]
        fn finish(&self) -> u64 {
            self.0.short_finish()
        }

        #[inline]
        fn write(&mut self, bytes: &[u8]) {
            self.0.write(bytes)
        }

        #[inline]
        fn write_u8(&mut self, i: u8) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u16(&mut self, i: u16) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u32(&mut self, i: u32) {
            self.write_u64(i as u64);
        }

        #[inline]
        fn write_u64(&mut self, i: u64) {
            self.0.write_u64(i);
        }

        #[inline]
        fn write_u128(&mut self, i: u128) {
            self.0.write_u128(i);
        }

        #[inline]
        fn write_usize(&mut self, i: usize) {
            self.0.write_usize(i);
        }
    }

    #[cfg(feature = "specialize")]
    pub(crate) struct AHasherStr(pub AHasher);

    /// A specialized hasher for a single string
    /// Note that the other types don't panic because the hash impl for String tacks on an unneeded call. (As does vec)
    #[cfg(feature = "specialize")]
    impl Hasher for AHasherStr {
        #[inline]
        fn finish(&self) -> u64 {
            self.0.finish()
        }

        #[inline]
        fn write(&mut self, bytes: &[u8]) {
            if bytes.len() > 8 {
                self.0.write(bytes)
            } else {
                let value = read_small(bytes);
                self.0.buffer = folded_multiply(value[0] ^ self.0.buffer,
                                               value[1] ^ self.0.extra_keys[1]);
                self.0.pad = self.0.pad.wrapping_add(bytes.len() as u64);
            }
        }

        #[inline]
        fn write_u8(&mut self, _i: u8) {}

        #[inline]
        fn write_u16(&mut self, _i: u16) {}

        #[inline]
        fn write_u32(&mut self, _i: u32) {}

        #[inline]
        fn write_u64(&mut self, _i: u64) {}

        #[inline]
        fn write_u128(&mut self, _i: u128) {}

        #[inline]
        fn write_usize(&mut self, _i: usize) {}
    }

    #[cfg(test)]
    mod tests {
        use crate::convert::Convert;
        use crate::fallback_hash::*;

        #[test]
        fn test_hash() {
            let mut hasher = AHasher::new_with_keys(0, 0);
            let value: u64 = 1 << 32;
            hasher.update(value);
            let result = hasher.buffer;
            let mut hasher = AHasher::new_with_keys(0, 0);
            let value2: u64 = 1;
            hasher.update(value2);
            let result2 = hasher.buffer;
            let result: [u8; 8] = result.convert();
            let result2: [u8; 8] = result2.convert();
            assert_ne!(hex::encode(result), hex::encode(result2));
        }

        #[test]
        fn test_conversion() {
            let input: &[u8] = "dddddddd".as_bytes();
            let bytes: u64 = as_array!(input, 8).convert();
            assert_eq!(bytes, 0x6464646464646464);
        }
    }