jzon-rs 0.2.2

Zero-copy JSON serialization with compile-time generated typed parsers
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
266
267
268
269
270
271
272
273
274

// SWAR: has_byte(x, t) = has_zero(x ^ repeat(t)); has_zero(v) = (v - 0x0101…01) & !v & 0x8080…80
// Each result byte is 0x80 if the input byte equals target, zero otherwise.

#[inline(always)]
const fn swar_has_byte(x: u64, target: u8) -> u64 {
    let rep = 0x0101_0101_0101_0101_u64.wrapping_mul(target as u64);
    let v = x ^ rep;
    v.wrapping_sub(0x0101_0101_0101_0101_u64) & !v & 0x8080_8080_8080_8080_u64
}

/// Scan `input[start..]` for the first `"` or `\` byte.
/// Returns the index in `input`, or `input.len()` if none found.
pub fn find_quote_or_backslash(input: &[u8], start: usize) -> usize {
    let mut i = start;

    while i + 8 <= input.len() {
        let chunk = u64::from_le_bytes(
            input[i..i + 8].try_into().expect("slice is 8 bytes"),
        );
        let m = swar_has_byte(chunk, b'"') | swar_has_byte(chunk, b'\\');
        if m != 0 {
            return i + (m.trailing_zeros() / 8) as usize;
        }
        i += 8;
    }

    while i < input.len() {
        if input[i] == b'"' || input[i] == b'\\' {
            return i;
        }
        i += 1;
    }
    i
}

#[cfg(feature = "simd")]
#[inline(always)]
const fn swar128_has_byte(x: u128, target: u8) -> u128 {
    let rep = 0x0101_0101_0101_0101_0101_0101_0101_0101_u128
        .wrapping_mul(target as u128);
    let v = x ^ rep;
    v.wrapping_sub(0x0101_0101_0101_0101_0101_0101_0101_0101_u128)
        & !v
        & 0x8080_8080_8080_8080_8080_8080_8080_8080_u128
}

#[cfg(feature = "simd")]
pub fn find_quote_or_backslash_simd16(input: &[u8], start: usize) -> usize {
    let mut i = start;

    while i + 16 <= input.len() {
        let chunk = {
            let mut b = [0u8; 16];
            b.copy_from_slice(&input[i..i + 16]);
            u128::from_le_bytes(b)
        };
        let m = swar128_has_byte(chunk, b'"') | swar128_has_byte(chunk, b'\\');
        if m != 0 {
            return i + (m.trailing_zeros() / 8) as usize;
        }
        i += 16;
    }

    find_quote_or_backslash(input, i)
}

#[cfg(all(feature = "simd", feature = "unstable"))]
pub fn find_quote_or_backslash_portable32(input: &[u8], start: usize) -> usize {
    use std::simd::{cmp::SimdPartialEq, num::SimdUint, u8x32};

    let quote  = u8x32::splat(b'"');
    let slash  = u8x32::splat(b'\\');
    let mut i  = start;

    while i + 32 <= input.len() {
        let chunk = u8x32::from_slice(&input[i..i + 32]);
        let m = chunk.simd_eq(quote) | chunk.simd_eq(slash);
        let mask = m.to_bitmask();
        if mask != 0 {
            return i + mask.trailing_zeros() as usize;
        }
        i += 32;
    }

    find_quote_or_backslash_simd16(input, i)
}

/// 64-byte lanes — compiler emits AVX-512/SVE/etc. automatically; Rust code is fully safe.
#[cfg(all(feature = "simd", feature = "unstable"))]
pub fn find_quote_or_backslash_portable64(input: &[u8], start: usize) -> usize {
    use std::simd::{cmp::SimdPartialEq, num::SimdUint, u8x64};

    let quote  = u8x64::splat(b'"');
    let slash  = u8x64::splat(b'\\');
    let mut i  = start;

    while i + 64 <= input.len() {
        let chunk = u8x64::from_slice(&input[i..i + 64]);
        let m = chunk.simd_eq(quote) | chunk.simd_eq(slash);
        let mask = m.to_bitmask();
        if mask != 0 {
            return i + mask.trailing_zeros() as usize;
        }
        i += 64;
    }

    find_quote_or_backslash_portable32(input, i)
}

/// Dispatch to the widest safe implementation available for this build.
#[inline]
pub fn find(input: &[u8], start: usize) -> usize {
    #[cfg(all(feature = "simd-intrinsics", target_arch = "aarch64"))]
    return crate::simd_arch::neon::find_quote_or_backslash_64(input, start);

    #[cfg(all(feature = "simd-intrinsics", target_arch = "x86_64"))]
    return crate::simd_arch::x86::find_quote_or_backslash_32(input, start);

    #[cfg(all(
        feature = "simd",
        feature = "unstable",
        not(any(
            all(feature = "simd-intrinsics", target_arch = "aarch64"),
            all(feature = "simd-intrinsics", target_arch = "x86_64"),
        )),
    ))]
    return find_quote_or_backslash_portable64(input, start);

    #[cfg(all(
        feature = "simd",
        not(feature = "unstable"),
        not(any(
            all(feature = "simd-intrinsics", target_arch = "aarch64"),
            all(feature = "simd-intrinsics", target_arch = "x86_64"),
        )),
    ))]
    return find_quote_or_backslash_simd16(input, start);

    #[cfg(not(feature = "simd"))]
    find_quote_or_backslash(input, start)
}

#[cfg(feature = "simd")]
#[allow(dead_code)] // used on non-aarch64 / when simd-intrinsics is off
#[inline(always)]
const fn swar128_has_ctrl(x: u128) -> u128 {
    // Bytes < 0x20: top 3 bits all zero.
    let masked = x & 0xE0E0_E0E0_E0E0_E0E0_E0E0_E0E0_E0E0_E0E0_u128;
    masked.wrapping_sub(0x0101_0101_0101_0101_0101_0101_0101_0101_u128)
        & !masked
        & 0x8080_8080_8080_8080_8080_8080_8080_8080_u128
}

/// Scan `input[start..]` for the first byte needing JSON string escaping
/// (`"`, `\`, or any byte < 0x20) using 16-byte u128 SWAR.
#[cfg(feature = "simd")]
#[allow(dead_code)]
pub fn find_escape_simd16(input: &[u8], start: usize) -> usize {
    let mut i = start;

    while i + 16 <= input.len() {
        let chunk = {
            let mut b = [0u8; 16];
            b.copy_from_slice(&input[i..i + 16]);
            u128::from_le_bytes(b)
        };
        let m = swar128_has_byte(chunk, b'"')
            | swar128_has_byte(chunk, b'\\')
            | swar128_has_ctrl(chunk);
        if m != 0 {
            return i + (m.trailing_zeros() / 8) as usize;
        }
        i += 16;
    }

    find_escape_scalar(input, i)
}

#[allow(dead_code)]
#[inline]
pub fn find_escape_scalar(input: &[u8], start: usize) -> usize {
    let mut i = start;
    while i < input.len() {
        let b = input[i];
        if b == b'"' || b == b'\\' || b < 0x20 {
            return i;
        }
        i += 1;
    }
    input.len()
}

/// Scan `input[start..]` for the first byte needing JSON string escaping using 32-byte portable SIMD.
#[cfg(all(feature = "simd", feature = "unstable"))]
fn find_escape_simd32(input: &[u8], start: usize) -> usize {
    use std::simd::{cmp::SimdPartialEq, cmp::SimdPartialOrd, u8x32};

    let quote     = u8x32::splat(b'"');
    let slash     = u8x32::splat(b'\\');
    let threshold = u8x32::splat(0x20u8);

    let mut i = start;
    while i + 32 <= input.len() {
        let chunk = u8x32::from_slice(&input[i..i + 32]);
        let needs_esc = chunk.simd_eq(quote)
            | chunk.simd_eq(slash)
            | chunk.simd_lt(threshold);
        let mask = needs_esc.to_bitmask();
        if mask != 0 {
            return i + mask.trailing_zeros() as usize;
        }
        i += 32;
    }
    find_escape_simd16(input, i)
}

/// Returns `true` if `slice` contains a raw control byte (< 0x20).
/// Uses SWAR to check 8 bytes per iteration — much faster than scalar for
/// typical string lengths (5-50 bytes all in L1 cache).
/// SWAR trick: byte b < 0x20 iff b.wrapping_sub(0x20) has its high bit set
/// AND the original byte did NOT have its high bit set (avoids catching 0x80+).
#[inline]
pub fn has_control_char(slice: &[u8]) -> bool {
    const REPEAT: u64 = 0x2020_2020_2020_2020_u64;
    const HIGH:   u64 = 0x8080_8080_8080_8080_u64;
    let mut i = 0;
    while i + 8 <= slice.len() {
        let chunk = u64::from_le_bytes(slice[i..i + 8].try_into().unwrap());
        // b < 0x20: (b - 0x20) wraps → high bit set; but also check ~b has high bit
        // (exclude bytes ≥ 0x80 which would wrap differently).
        if (chunk.wrapping_sub(REPEAT) & !chunk & HIGH) != 0 {
            return true;
        }
        i += 8;
    }
    while i < slice.len() {
        if slice[i] < 0x20 { return true; }
        i += 1;
    }
    false
}

/// Find the first byte needing JSON string escaping (`"`, `\`, or `< 0x20`).
#[inline]
pub fn find_escape(input: &[u8], start: usize) -> usize {
    #[cfg(all(feature = "simd-intrinsics", target_arch = "aarch64"))]
    return crate::simd_arch::neon::find_escape_64(input, start);

    #[cfg(all(feature = "simd-intrinsics", target_arch = "x86_64"))]
    return crate::simd_arch::x86::find_escape_32(input, start);

    #[cfg(all(
        feature = "simd",
        feature = "unstable",
        not(any(
            all(feature = "simd-intrinsics", target_arch = "aarch64"),
            all(feature = "simd-intrinsics", target_arch = "x86_64"),
        )),
    ))]
    return find_escape_simd32(input, start);

    #[cfg(all(
        feature = "simd",
        not(feature = "unstable"),
        not(any(
            all(feature = "simd-intrinsics", target_arch = "aarch64"),
            all(feature = "simd-intrinsics", target_arch = "x86_64"),
        )),
    ))]
    return find_escape_simd16(input, start);

    #[cfg(not(feature = "simd"))]
    find_escape_scalar(input, start)
}