1#[cfg(target_arch = "x86")]
2use core::arch::x86 as arch;
3#[cfg(target_arch = "x86_64")]
4use core::arch::x86_64 as arch;
5
6#[derive(Clone)]
7pub struct State {
8 state: u32,
9}
10
11impl State {
12 #[cfg(not(feature = "std"))]
13 pub fn new(state: u32) -> Option<Self> {
14 if cfg!(target_feature = "pclmulqdq")
15 && cfg!(target_feature = "sse2")
16 && cfg!(target_feature = "sse4.1")
17 {
18 // SAFETY: The conditions above ensure that all
19 // required instructions are supported by the CPU.
20 Some(Self { state })
21 } else {
22 None
23 }
24 }
25
26 #[cfg(feature = "std")]
27 pub fn new(state: u32) -> Option<Self> {
28 if is_x86_feature_detected!("pclmulqdq")
29 && is_x86_feature_detected!("sse2")
30 && is_x86_feature_detected!("sse4.1")
31 {
32 // SAFETY: The conditions above ensure that all
33 // required instructions are supported by the CPU.
34 Some(Self { state })
35 } else {
36 None
37 }
38 }
39
40 pub fn update(&mut self, buf: &[u8]) {
41 // SAFETY: The `State::new` constructor ensures that all
42 // required instructions are supported by the CPU.
43 self.state = unsafe { calculate(self.state, buf) }
44 }
45
46 pub fn finalize(self) -> u32 {
47 self.state
48 }
49
50 pub fn reset(&mut self) {
51 self.state = 0;
52 }
53
54 pub fn combine(&mut self, other: u32, amount: u64) {
55 self.state = ::combine::combine(self.state, other, amount);
56 }
57}
58
59const K1: i64 = 0x154442bd4;
60const K2: i64 = 0x1c6e41596;
61const K3: i64 = 0x1751997d0;
62const K4: i64 = 0x0ccaa009e;
63const K5: i64 = 0x163cd6124;
64
65const P_X: i64 = 0x1DB710641;
66const U_PRIME: i64 = 0x1F7011641;
67
68#[cfg(feature = "std")]
69unsafe fn debug(s: &str, a: arch::__m128i) -> arch::__m128i {
70 if false {
71 union A {
72 a: arch::__m128i,
73 b: [u8; 16],
74 }
75 let x: [u8; 16] = A { a }.b;
76 print!(" {:20} | ", s);
77 for x: &u8 in x.iter() {
78 print!("{:02x} ", x);
79 }
80 println!();
81 }
82 return a;
83}
84
85#[cfg(not(feature = "std"))]
86unsafe fn debug(_s: &str, a: arch::__m128i) -> arch::__m128i {
87 a
88}
89
90#[target_feature(enable = "pclmulqdq", enable = "sse2", enable = "sse4.1")]
91unsafe fn calculate(crc: u32, mut data: &[u8]) -> u32 {
92 // In theory we can accelerate smaller chunks too, but for now just rely on
93 // the fallback implementation as it's too much hassle and doesn't seem too
94 // beneficial.
95 if data.len() < 128 {
96 return ::baseline::update_fast_16(crc, data);
97 }
98
99 // Step 1: fold by 4 loop
100 let mut x3 = get(&mut data);
101 let mut x2 = get(&mut data);
102 let mut x1 = get(&mut data);
103 let mut x0 = get(&mut data);
104
105 // fold in our initial value, part of the incremental crc checksum
106 x3 = arch::_mm_xor_si128(x3, arch::_mm_cvtsi32_si128(!crc as i32));
107
108 let k1k2 = arch::_mm_set_epi64x(K2, K1);
109 while data.len() >= 64 {
110 x3 = reduce128(x3, get(&mut data), k1k2);
111 x2 = reduce128(x2, get(&mut data), k1k2);
112 x1 = reduce128(x1, get(&mut data), k1k2);
113 x0 = reduce128(x0, get(&mut data), k1k2);
114 }
115
116 let k3k4 = arch::_mm_set_epi64x(K4, K3);
117 let mut x = reduce128(x3, x2, k3k4);
118 x = reduce128(x, x1, k3k4);
119 x = reduce128(x, x0, k3k4);
120
121 // Step 2: fold by 1 loop
122 while data.len() >= 16 {
123 x = reduce128(x, get(&mut data), k3k4);
124 }
125
126 debug("128 > 64 init", x);
127
128 // Perform step 3, reduction from 128 bits to 64 bits. This is
129 // significantly different from the paper and basically doesn't follow it
130 // at all. It's not really clear why, but implementations of this algorithm
131 // in Chrome/Linux diverge in the same way. It is beyond me why this is
132 // different than the paper, maybe the paper has like errata or something?
133 // Unclear.
134 //
135 // It's also not clear to me what's actually happening here and/or why, but
136 // algebraically what's happening is:
137 //
138 // x = (x[0:63] • K4) ^ x[64:127] // 96 bit result
139 // x = ((x[0:31] as u64) • K5) ^ x[32:95] // 64 bit result
140 //
141 // It's... not clear to me what's going on here. The paper itself is pretty
142 // vague on this part but definitely uses different constants at least.
143 // It's not clear to me, reading the paper, where the xor operations are
144 // happening or why things are shifting around. This implementation...
145 // appears to work though!
146 let x = arch::_mm_xor_si128(
147 arch::_mm_clmulepi64_si128(x, k3k4, 0x10),
148 arch::_mm_srli_si128(x, 8),
149 );
150 let x = arch::_mm_xor_si128(
151 arch::_mm_clmulepi64_si128(
152 arch::_mm_and_si128(x, arch::_mm_set_epi32(0, 0, 0, !0)),
153 arch::_mm_set_epi64x(0, K5),
154 0x00,
155 ),
156 arch::_mm_srli_si128(x, 4),
157 );
158 debug("128 > 64 xx", x);
159
160 // Perform a Barrett reduction from our now 64 bits to 32 bits. The
161 // algorithm for this is described at the end of the paper, and note that
162 // this also implements the "bit reflected input" variant.
163 let pu = arch::_mm_set_epi64x(U_PRIME, P_X);
164
165 // T1(x) = ⌊(R(x) % x^32)⌋ • μ
166 let t1 = arch::_mm_clmulepi64_si128(
167 arch::_mm_and_si128(x, arch::_mm_set_epi32(0, 0, 0, !0)),
168 pu,
169 0x10,
170 );
171 // T2(x) = ⌊(T1(x) % x^32)⌋ • P(x)
172 let t2 = arch::_mm_clmulepi64_si128(
173 arch::_mm_and_si128(t1, arch::_mm_set_epi32(0, 0, 0, !0)),
174 pu,
175 0x00,
176 );
177 // We're doing the bit-reflected variant, so get the upper 32-bits of the
178 // 64-bit result instead of the lower 32-bits.
179 //
180 // C(x) = R(x) ^ T2(x) / x^32
181 let c = arch::_mm_extract_epi32(arch::_mm_xor_si128(x, t2), 1) as u32;
182
183 if !data.is_empty() {
184 ::baseline::update_fast_16(!c, data)
185 } else {
186 !c
187 }
188}
189
190unsafe fn reduce128(a: arch::__m128i, b: arch::__m128i, keys: arch::__m128i) -> arch::__m128i {
191 let t1: __m128i = arch::_mm_clmulepi64_si128(a, b:keys, 0x00);
192 let t2: __m128i = arch::_mm_clmulepi64_si128(a, b:keys, 0x11);
193 arch::_mm_xor_si128(a:arch::_mm_xor_si128(b, t1), b:t2)
194}
195
196unsafe fn get(a: &mut &[u8]) -> arch::__m128i {
197 debug_assert!(a.len() >= 16);
198 let r: __m128i = arch::_mm_loadu_si128(mem_addr:a.as_ptr() as *const arch::__m128i);
199 *a = &a[16..];
200 return r;
201}
202
203#[cfg(test)]
204mod test {
205 quickcheck! {
206 fn check_against_baseline(init: u32, chunks: Vec<(Vec<u8>, usize)>) -> bool {
207 let mut baseline = super::super::super::baseline::State::new(init);
208 let mut pclmulqdq = super::State::new(init).expect("not supported");
209 for (chunk, mut offset) in chunks {
210 // simulate random alignments by offsetting the slice by up to 15 bytes
211 offset &= 0xF;
212 if chunk.len() <= offset {
213 baseline.update(&chunk);
214 pclmulqdq.update(&chunk);
215 } else {
216 baseline.update(&chunk[offset..]);
217 pclmulqdq.update(&chunk[offset..]);
218 }
219 }
220 pclmulqdq.finalize() == baseline.finalize()
221 }
222 }
223}
224