1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Hardware-accelerated CRC-32 variants for Linux on z Systems
4 *
5 * Use the z/Architecture Vector Extension Facility to accelerate the
6 * computing of CRC-32 checksums.
7 *
8 * This CRC-32 implementation algorithm processes the most-significant
9 * bit first (BE).
10 *
11 * Copyright IBM Corp. 2015
12 * Author(s): Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
13 */
14
15#include <linux/types.h>
16#include <asm/fpu.h>
17#include "crc32-vx.h"
18
19/* Vector register range containing CRC-32 constants */
20#define CONST_R1R2 9
21#define CONST_R3R4 10
22#define CONST_R5 11
23#define CONST_R6 12
24#define CONST_RU_POLY 13
25#define CONST_CRC_POLY 14
26
27/*
28 * The CRC-32 constant block contains reduction constants to fold and
29 * process particular chunks of the input data stream in parallel.
30 *
31 * For the CRC-32 variants, the constants are precomputed according to
32 * these definitions:
33 *
34 * R1 = x4*128+64 mod P(x)
35 * R2 = x4*128 mod P(x)
36 * R3 = x128+64 mod P(x)
37 * R4 = x128 mod P(x)
38 * R5 = x96 mod P(x)
39 * R6 = x64 mod P(x)
40 *
41 * Barret reduction constant, u, is defined as floor(x**64 / P(x)).
42 *
43 * where P(x) is the polynomial in the normal domain and the P'(x) is the
44 * polynomial in the reversed (bitreflected) domain.
45 *
46 * Note that the constant definitions below are extended in order to compute
47 * intermediate results with a single VECTOR GALOIS FIELD MULTIPLY instruction.
48 * The rightmost doubleword can be 0 to prevent contribution to the result or
49 * can be multiplied by 1 to perform an XOR without the need for a separate
50 * VECTOR EXCLUSIVE OR instruction.
51 *
52 * CRC-32 (IEEE 802.3 Ethernet, ...) polynomials:
53 *
54 * P(x) = 0x04C11DB7
55 * P'(x) = 0xEDB88320
56 */
57
58static unsigned long constants_CRC_32_BE[] = {
59 0x08833794c, 0x0e6228b11, /* R1, R2 */
60 0x0c5b9cd4c, 0x0e8a45605, /* R3, R4 */
61 0x0f200aa66, 1UL << 32, /* R5, x32 */
62 0x0490d678d, 1, /* R6, 1 */
63 0x104d101df, 0, /* u */
64 0x104C11DB7, 0, /* P(x) */
65};
66
67/**
68 * crc32_be_vgfm_16 - Compute CRC-32 (BE variant) with vector registers
69 * @crc: Initial CRC value, typically ~0.
70 * @buf: Input buffer pointer, performance might be improved if the
71 * buffer is on a doubleword boundary.
72 * @size: Size of the buffer, must be 64 bytes or greater.
73 *
74 * Register usage:
75 * V0: Initial CRC value and intermediate constants and results.
76 * V1..V4: Data for CRC computation.
77 * V5..V8: Next data chunks that are fetched from the input buffer.
78 * V9..V14: CRC-32 constants.
79 */
80u32 crc32_be_vgfm_16(u32 crc, unsigned char const *buf, size_t size)
81{
82 /* Load CRC-32 constants */
83 fpu_vlm(CONST_R1R2, CONST_CRC_POLY, &constants_CRC_32_BE);
84 fpu_vzero(0);
85
86 /* Load the initial CRC value into the leftmost word of V0. */
87 fpu_vlvgf(0, crc, 0);
88
89 /* Load a 64-byte data chunk and XOR with CRC */
90 fpu_vlm(1, 4, buf);
91 fpu_vx(1, 0, 1);
92 buf += 64;
93 size -= 64;
94
95 while (size >= 64) {
96 /* Load the next 64-byte data chunk into V5 to V8 */
97 fpu_vlm(5, 8, buf);
98
99 /*
100 * Perform a GF(2) multiplication of the doublewords in V1 with
101 * the reduction constants in V0. The intermediate result is
102 * then folded (accumulated) with the next data chunk in V5 and
103 * stored in V1. Repeat this step for the register contents
104 * in V2, V3, and V4 respectively.
105 */
106 fpu_vgfmag(1, CONST_R1R2, 1, 5);
107 fpu_vgfmag(2, CONST_R1R2, 2, 6);
108 fpu_vgfmag(3, CONST_R1R2, 3, 7);
109 fpu_vgfmag(4, CONST_R1R2, 4, 8);
110 buf += 64;
111 size -= 64;
112 }
113
114 /* Fold V1 to V4 into a single 128-bit value in V1 */
115 fpu_vgfmag(1, CONST_R3R4, 1, 2);
116 fpu_vgfmag(1, CONST_R3R4, 1, 3);
117 fpu_vgfmag(1, CONST_R3R4, 1, 4);
118
119 while (size >= 16) {
120 fpu_vl(2, buf);
121 fpu_vgfmag(1, CONST_R3R4, 1, 2);
122 buf += 16;
123 size -= 16;
124 }
125
126 /*
127 * The R5 constant is used to fold a 128-bit value into an 96-bit value
128 * that is XORed with the next 96-bit input data chunk. To use a single
129 * VGFMG instruction, multiply the rightmost 64-bit with x^32 (1<<32) to
130 * form an intermediate 96-bit value (with appended zeros) which is then
131 * XORed with the intermediate reduction result.
132 */
133 fpu_vgfmg(1, CONST_R5, 1);
134
135 /*
136 * Further reduce the remaining 96-bit value to a 64-bit value using a
137 * single VGFMG, the rightmost doubleword is multiplied with 0x1. The
138 * intermediate result is then XORed with the product of the leftmost
139 * doubleword with R6. The result is a 64-bit value and is subject to
140 * the Barret reduction.
141 */
142 fpu_vgfmg(1, CONST_R6, 1);
143
144 /*
145 * The input values to the Barret reduction are the degree-63 polynomial
146 * in V1 (R(x)), degree-32 generator polynomial, and the reduction
147 * constant u. The Barret reduction result is the CRC value of R(x) mod
148 * P(x).
149 *
150 * The Barret reduction algorithm is defined as:
151 *
152 * 1. T1(x) = floor( R(x) / x^32 ) GF2MUL u
153 * 2. T2(x) = floor( T1(x) / x^32 ) GF2MUL P(x)
154 * 3. C(x) = R(x) XOR T2(x) mod x^32
155 *
156 * Note: To compensate the division by x^32, use the vector unpack
157 * instruction to move the leftmost word into the leftmost doubleword
158 * of the vector register. The rightmost doubleword is multiplied
159 * with zero to not contribute to the intermediate results.
160 */
161
162 /* T1(x) = floor( R(x) / x^32 ) GF2MUL u */
163 fpu_vupllf(2, 1);
164 fpu_vgfmg(2, CONST_RU_POLY, 2);
165
166 /*
167 * Compute the GF(2) product of the CRC polynomial in VO with T1(x) in
168 * V2 and XOR the intermediate result, T2(x), with the value in V1.
169 * The final result is in the rightmost word of V2.
170 */
171 fpu_vupllf(2, 2);
172 fpu_vgfmag(2, CONST_CRC_POLY, 2, 1);
173 return fpu_vlgvf(2, 3);
174}
175

source code of linux/lib/crc/s390/crc32be-vx.c