jiter 0.15.0

Fast Iterable JSON parser
Documentation 
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

use std::mem::transmute;
#[rustfmt::skip]
use std::arch::aarch64::{
    uint8x16_t,
    uint16x8_t,
    uint32x4_t,
    uint64x2_t,
    uint8x8_t,
    uint16x4_t,
    uint32x2_t,
    uint64x1_t,
    // 16 byte methods
    vld1q_u8 as simd_load_16,
    vcgtq_u8 as simd_gt_16,
    vcltq_u8 as simd_lt_16,
    vorrq_u8 as simd_or_16,
    vceqq_u8 as simd_eq_16,
    vextq_u8 as combine_vecs_16,
    vsubq_u8 as simd_sub_16,
    vmulq_u8 as simd_mul_16,
    vpaddlq_u8 as simd_add_16,
    vmulq_u16 as simd_mul_u16_8,
    vpaddlq_u16 as simd_add_u16_8,
    vmulq_u32 as simd_mul_u32_4,
    vpaddlq_u32 as simd_add_u32_4,
    // 8 byte methods
    vget_low_u8 as simd_get_low,
    vext_u8 as combine_vecs_8,
    vsub_u8 as simd_sub_8,
    vmul_u8 as simd_mul_8,
    vpaddl_u8 as simd_add_8,
    vmul_u16 as simd_mul_u16_4,
    vpaddl_u16 as simd_add_u16_4,
    vmul_u32 as simd_mul_u32_2,
    vpaddl_u32 as simd_add_u32_2,
};
use crate::JsonResult;

use crate::number_decoder::{IntChunk, decode_int_chunk_fallback};
use crate::string_decoder::StringChunk;

type SimdVecu8_16 = uint8x16_t;
type SimdVecu16_8 = uint16x8_t;
type SimdVecu32_4 = uint32x4_t;
type SimdVecu64_2 = uint64x2_t;

type SimdVecu8_8 = uint8x8_t;
type SimdVecu16_4 = uint16x4_t;
type SimdVecu32_2 = uint32x2_t;
type SimdVecu64_1 = uint64x1_t;
const SIMD_STEP: usize = 16;

macro_rules! simd_const {
    ($array:expr) => {
        unsafe { transmute($array) }
    };
}

const ZERO_DIGIT_U8_8: SimdVecu8_8 = simd_const!([b'0'; 8]);
const ZERO_VAL_U8_8: SimdVecu8_8 = simd_const!([0u8; 8]);
const ALT_MUL_U8_8: SimdVecu8_8 = simd_const!([10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8]);
const ALT_MUL_U16_4: SimdVecu16_4 = simd_const!([100u16, 1u16, 100u16, 1u16]);
const ALT_MUL_U32_2: SimdVecu32_2 = simd_const!([10000u32, 1u32]);
const ZERO_DIGIT_16: SimdVecu8_16 = simd_const!([b'0'; 16]);
const NINE_DIGIT_16: SimdVecu8_16 = simd_const!([b'9'; 16]);

const ZERO_VAL_U8_16: SimdVecu8_16 = simd_const!([0u8; 16]);
const ALT_MUL_U8_16: SimdVecu8_16 = simd_const!([
    10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8, 10u8, 1u8
]);
const ALT_MUL_U16_8: SimdVecu16_8 = simd_const!([100u16, 1u16, 100u16, 1u16, 100u16, 1u16, 100u16, 1u16]);
const ALT_MUL_U32_4: SimdVecu32_4 = simd_const!([10000u32, 1u32, 10000u32, 1u32]);

#[inline(always)]
pub(crate) fn decode_int_chunk(data: &[u8], index: usize) -> (IntChunk, usize) {
    if let Some(byte_chunk) = data.get(index..index + SIMD_STEP) {
        let byte_vec = load_slice(byte_chunk);

        let digit_mask = get_digit_mask(byte_vec);
        if is_zero(digit_mask) {
            // all lanes are digits, parse the full vector
            let value = unsafe { full_calc(byte_vec, 16) };
            (IntChunk::Ongoing(value), index + SIMD_STEP)
        } else {
            // some lanes are not digits, transmute to a pair of u64 and find the first non-digit
            let last_digit = find_end(digit_mask);
            let index = index + last_digit as usize;
            if next_is_float(data, index) {
                (IntChunk::Float, index)
            } else if last_digit <= 8 {
                // none-digit in the first 8 bytes
                let value = unsafe { first_half_calc(byte_vec, last_digit) };
                (IntChunk::Done(value), index)
            } else {
                // none-digit in the last 8 bytes
                let value = unsafe { full_calc(byte_vec, last_digit) };
                (IntChunk::Done(value), index)
            }
        }
    } else {
        // we got near the end of the string, fall back to the slow path
        decode_int_chunk_fallback(data, index, 0)
    }
}

#[rustfmt::skip]
fn get_digit_mask(byte_vec: SimdVecu8_16) -> SimdVecu8_16 {
    unsafe {
        simd_or_16(
            simd_lt_16(byte_vec, ZERO_DIGIT_16),
            simd_gt_16(byte_vec, NINE_DIGIT_16),
        )
    }
}

unsafe fn first_half_calc(byte_vec: SimdVecu8_16, last_digit: u32) -> u64 {
    unsafe {
        let small_byte_vec = simd_get_low(byte_vec);
        // subtract ascii '0' from every byte to get the digit values
        let digits: SimdVecu8_8 = simd_sub_8(small_byte_vec, ZERO_DIGIT_U8_8);
        let digits = match last_digit {
            0 => return 0,
            1 => {
                let t: [u8; 8] = transmute(digits);
                return t[0] as u64;
            }
            2 => combine_vecs_8::<2>(ZERO_VAL_U8_8, digits),
            3 => combine_vecs_8::<3>(ZERO_VAL_U8_8, digits),
            4 => combine_vecs_8::<4>(ZERO_VAL_U8_8, digits),
            5 => combine_vecs_8::<5>(ZERO_VAL_U8_8, digits),
            6 => combine_vecs_8::<6>(ZERO_VAL_U8_8, digits),
            7 => combine_vecs_8::<7>(ZERO_VAL_U8_8, digits),
            8 => digits,
            _ => unreachable!("last_digit should be less than 8"),
        };
        // multiple every other digit by 10
        let x: SimdVecu8_8 = simd_mul_8(digits, ALT_MUL_U8_8);
        // add the value together and combine the 8x8-bit lanes into 4x16-bit lanes
        let x: SimdVecu16_4 = simd_add_8(x);
        // multiple every other digit by 100
        let x: SimdVecu16_4 = simd_mul_u16_4(x, ALT_MUL_U16_4);
        // add the value together and combine the 4x16-bit lanes into 2x32-bit lanes
        let x: SimdVecu32_2 = simd_add_u16_4(x);
        // multiple the first value 10000
        let x: SimdVecu32_2 = simd_mul_u32_2(x, ALT_MUL_U32_2);
        // add the value together and combine the 2x32-bit lanes into 1x64-bit lane
        let x: SimdVecu64_1 = simd_add_u32_2(x);
        // transmute the 64-bit lane into a u64
        transmute(x)
    }
}

unsafe fn full_calc(byte_vec: SimdVecu8_16, last_digit: u32) -> u64 {
    unsafe {
        // subtract ascii '0' from every byte to get the digit values
        let digits: SimdVecu8_16 = simd_sub_16(byte_vec, ZERO_DIGIT_16);
        let digits = match last_digit {
            9 => combine_vecs_16::<9>(ZERO_VAL_U8_16, digits),
            10 => combine_vecs_16::<10>(ZERO_VAL_U8_16, digits),
            11 => combine_vecs_16::<11>(ZERO_VAL_U8_16, digits),
            12 => combine_vecs_16::<12>(ZERO_VAL_U8_16, digits),
            13 => combine_vecs_16::<13>(ZERO_VAL_U8_16, digits),
            14 => combine_vecs_16::<14>(ZERO_VAL_U8_16, digits),
            15 => combine_vecs_16::<15>(ZERO_VAL_U8_16, digits),
            16 => digits,
            _ => unreachable!("last_digit should be between 9 and 16"),
        };
        // multiple every other digit by 10
        let x: SimdVecu8_16 = simd_mul_16(digits, ALT_MUL_U8_16);
        // add the value together and combine the 16x8-bit lanes into 8x16-bit lanes
        let x: SimdVecu16_8 = simd_add_16(x);
        // multiple every other digit by 100
        let x: SimdVecu16_8 = simd_mul_u16_8(x, ALT_MUL_U16_8);
        // add the value together and combine the 8x16-bit lanes into 4x32-bit lanes
        let x: SimdVecu32_4 = simd_add_u16_8(x);
        // multiple every other digit by 10000
        let x: SimdVecu32_4 = simd_mul_u32_4(x, ALT_MUL_U32_4);
        // add the value together and combine the 4x32-bit lanes into 2x64-bit lane
        let x: SimdVecu64_2 = simd_add_u32_4(x);

        // transmute the 2x64-bit lane into an array;
        let t: [u64; 2] = transmute(x);
        // since the data started out as digits, it's safe to assume the result fits in a u64
        t[0].wrapping_mul(100_000_000).wrapping_add(t[1])
    }
}

fn next_is_float(data: &[u8], index: usize) -> bool {
    let next = unsafe { data.get_unchecked(index) };
    matches!(next, b'.' | b'e' | b'E')
}

const QUOTE_16: SimdVecu8_16 = simd_const!([b'"'; 16]);
const BACKSLASH_16: SimdVecu8_16 = simd_const!([b'\\'; 16]);
// values below 32 are control characters
const CONTROL_16: SimdVecu8_16 = simd_const!([32u8; 16]);
const ASCII_MAX_16: SimdVecu8_16 = simd_const!([127u8; 16]);

#[inline(always)]
pub(crate) fn decode_string_chunk(
    data: &[u8],
    mut index: usize,
    mut ascii_only: bool,
    allow_partial: bool,
) -> JsonResult<(StringChunk, bool, usize)> {
    while let Some(byte_chunk) = data.get(index..index + SIMD_STEP) {
        let byte_vec = load_slice(byte_chunk);

        let ascii_mask = string_ascii_mask(byte_vec);
        if is_zero(ascii_mask) {
            // this chunk is just ascii, continue to the next chunk
            index += SIMD_STEP;
        } else {
            // this chunk contains either a stop character or a non-ascii character
            let a: [u8; 16] = unsafe { transmute(byte_vec) };
            #[allow(clippy::redundant_else)]
            if let Some(r) = StringChunk::decode_array(a, &mut index, ascii_only) {
                return r;
            } else {
                ascii_only = false;
            }
        }
    }
    // we got near the end of the string, fall back to the slow path
    StringChunk::decode_fallback(data, index, ascii_only, allow_partial)
}

#[rustfmt::skip]
/// returns a mask where any non-zero byte means we don't have a simple ascii character, either
/// quote, backslash, control character, or non-ascii (above 127)
fn string_ascii_mask(byte_vec: SimdVecu8_16) -> SimdVecu8_16 {
    unsafe {
        simd_or_16(
            simd_eq_16(byte_vec, QUOTE_16),
            simd_or_16(
                simd_eq_16(byte_vec, BACKSLASH_16),
                simd_or_16(
                    simd_gt_16(byte_vec, ASCII_MAX_16),
                    simd_lt_16(byte_vec, CONTROL_16),
                )
            )
        )
    }
}

fn find_end(digit_mask: SimdVecu8_16) -> u32 {
    let t: [u64; 2] = unsafe { transmute(digit_mask) };
    if t[0] != 0 {
        // non-digit in the first 8 bytes
        t[0].trailing_zeros() / 8
    } else {
        t[1].trailing_zeros() / 8 + 8
    }
}

/// return true if all bytes are zero
fn is_zero(vec: SimdVecu8_16) -> bool {
    let t: [u64; 2] = unsafe { transmute(vec) };
    t[0] == 0 && t[1] == 0
}

fn load_slice(bytes: &[u8]) -> SimdVecu8_16 {
    debug_assert_eq!(bytes.len(), 16);
    unsafe { simd_load_16(bytes.as_ptr()) }
}