xref: /openbmc/linux/arch/s390/crypto/crc32be-vx.S (revision a36954f5)
1/*
2 * Hardware-accelerated CRC-32 variants for Linux on z Systems
3 *
4 * Use the z/Architecture Vector Extension Facility to accelerate the
5 * computing of CRC-32 checksums.
6 *
7 * This CRC-32 implementation algorithm processes the most-significant
8 * bit first (BE).
9 *
10 * Copyright IBM Corp. 2015
11 * Author(s): Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
12 */
13
14#include <linux/linkage.h>
15#include <asm/vx-insn.h>
16
17/* Vector register range containing CRC-32 constants */
18#define CONST_R1R2		%v9
19#define CONST_R3R4		%v10
20#define CONST_R5		%v11
21#define CONST_R6		%v12
22#define CONST_RU_POLY		%v13
23#define CONST_CRC_POLY		%v14
24
25.data
26.align 8
27
28/*
29 * The CRC-32 constant block contains reduction constants to fold and
30 * process particular chunks of the input data stream in parallel.
31 *
32 * For the CRC-32 variants, the constants are precomputed according to
33 * these defintions:
34 *
35 *	R1 = x4*128+64 mod P(x)
36 *	R2 = x4*128    mod P(x)
37 *	R3 = x128+64   mod P(x)
38 *	R4 = x128      mod P(x)
39 *	R5 = x96       mod P(x)
40 *	R6 = x64       mod P(x)
41 *
42 *	Barret reduction constant, u, is defined as floor(x**64 / P(x)).
43 *
44 *	where P(x) is the polynomial in the normal domain and the P'(x) is the
45 *	polynomial in the reversed (bitreflected) domain.
46 *
47 * Note that the constant definitions below are extended in order to compute
48 * intermediate results with a single VECTOR GALOIS FIELD MULTIPLY instruction.
49 * The righmost doubleword can be 0 to prevent contribution to the result or
50 * can be multiplied by 1 to perform an XOR without the need for a separate
51 * VECTOR EXCLUSIVE OR instruction.
52 *
53 * CRC-32 (IEEE 802.3 Ethernet, ...) polynomials:
54 *
55 *	P(x)  = 0x04C11DB7
56 *	P'(x) = 0xEDB88320
57 */
58
59.Lconstants_CRC_32_BE:
60	.quad		0x08833794c, 0x0e6228b11	# R1, R2
61	.quad		0x0c5b9cd4c, 0x0e8a45605	# R3, R4
62	.quad		0x0f200aa66, 1 << 32		# R5, x32
63	.quad		0x0490d678d, 1			# R6, 1
64	.quad		0x104d101df, 0			# u
65	.quad		0x104C11DB7, 0			# P(x)
66
67.previous
68
69.text
70/*
71 * The CRC-32 function(s) use these calling conventions:
72 *
73 * Parameters:
74 *
75 *	%r2:	Initial CRC value, typically ~0; and final CRC (return) value.
76 *	%r3:	Input buffer pointer, performance might be improved if the
77 *		buffer is on a doubleword boundary.
78 *	%r4:	Length of the buffer, must be 64 bytes or greater.
79 *
80 * Register usage:
81 *
82 *	%r5:	CRC-32 constant pool base pointer.
83 *	V0:	Initial CRC value and intermediate constants and results.
84 *	V1..V4:	Data for CRC computation.
85 *	V5..V8:	Next data chunks that are fetched from the input buffer.
86 *
87 *	V9..V14: CRC-32 constants.
88 */
89ENTRY(crc32_be_vgfm_16)
90	/* Load CRC-32 constants */
91	larl	%r5,.Lconstants_CRC_32_BE
92	VLM	CONST_R1R2,CONST_CRC_POLY,0,%r5
93
94	/* Load the initial CRC value into the leftmost word of V0. */
95	VZERO	%v0
96	VLVGF	%v0,%r2,0
97
98	/* Load a 64-byte data chunk and XOR with CRC */
99	VLM	%v1,%v4,0,%r3		/* 64-bytes into V1..V4 */
100	VX	%v1,%v0,%v1		/* V1 ^= CRC */
101	aghi	%r3,64			/* BUF = BUF + 64 */
102	aghi	%r4,-64			/* LEN = LEN - 64 */
103
104	/* Check remaining buffer size and jump to proper folding method */
105	cghi	%r4,64
106	jl	.Lless_than_64bytes
107
108.Lfold_64bytes_loop:
109	/* Load the next 64-byte data chunk into V5 to V8 */
110	VLM	%v5,%v8,0,%r3
111
112	/*
113	 * Perform a GF(2) multiplication of the doublewords in V1 with
114	 * the reduction constants in V0.  The intermediate result is
115	 * then folded (accumulated) with the next data chunk in V5 and
116	 * stored in V1.  Repeat this step for the register contents
117	 * in V2, V3, and V4 respectively.
118	 */
119	VGFMAG	%v1,CONST_R1R2,%v1,%v5
120	VGFMAG	%v2,CONST_R1R2,%v2,%v6
121	VGFMAG	%v3,CONST_R1R2,%v3,%v7
122	VGFMAG	%v4,CONST_R1R2,%v4,%v8
123
124	/* Adjust buffer pointer and length for next loop */
125	aghi	%r3,64			/* BUF = BUF + 64 */
126	aghi	%r4,-64			/* LEN = LEN - 64 */
127
128	cghi	%r4,64
129	jnl	.Lfold_64bytes_loop
130
131.Lless_than_64bytes:
132	/* Fold V1 to V4 into a single 128-bit value in V1 */
133	VGFMAG	%v1,CONST_R3R4,%v1,%v2
134	VGFMAG	%v1,CONST_R3R4,%v1,%v3
135	VGFMAG	%v1,CONST_R3R4,%v1,%v4
136
137	/* Check whether to continue with 64-bit folding */
138	cghi	%r4,16
139	jl	.Lfinal_fold
140
141.Lfold_16bytes_loop:
142
143	VL	%v2,0,,%r3		/* Load next data chunk */
144	VGFMAG	%v1,CONST_R3R4,%v1,%v2	/* Fold next data chunk */
145
146	/* Adjust buffer pointer and size for folding next data chunk */
147	aghi	%r3,16
148	aghi	%r4,-16
149
150	/* Process remaining data chunks */
151	cghi	%r4,16
152	jnl	.Lfold_16bytes_loop
153
154.Lfinal_fold:
155	/*
156	 * The R5 constant is used to fold a 128-bit value into an 96-bit value
157	 * that is XORed with the next 96-bit input data chunk.  To use a single
158	 * VGFMG instruction, multiply the rightmost 64-bit with x^32 (1<<32) to
159	 * form an intermediate 96-bit value (with appended zeros) which is then
160	 * XORed with the intermediate reduction result.
161	 */
162	VGFMG	%v1,CONST_R5,%v1
163
164	/*
165	 * Further reduce the remaining 96-bit value to a 64-bit value using a
166	 * single VGFMG, the rightmost doubleword is multiplied with 0x1. The
167	 * intermediate result is then XORed with the product of the leftmost
168	 * doubleword with R6.	The result is a 64-bit value and is subject to
169	 * the Barret reduction.
170	 */
171	VGFMG	%v1,CONST_R6,%v1
172
173	/*
174	 * The input values to the Barret reduction are the degree-63 polynomial
175	 * in V1 (R(x)), degree-32 generator polynomial, and the reduction
176	 * constant u.	The Barret reduction result is the CRC value of R(x) mod
177	 * P(x).
178	 *
179	 * The Barret reduction algorithm is defined as:
180	 *
181	 *    1. T1(x) = floor( R(x) / x^32 ) GF2MUL u
182	 *    2. T2(x) = floor( T1(x) / x^32 ) GF2MUL P(x)
183	 *    3. C(x)  = R(x) XOR T2(x) mod x^32
184	 *
185	 * Note: To compensate the division by x^32, use the vector unpack
186	 * instruction to move the leftmost word into the leftmost doubleword
187	 * of the vector register.  The rightmost doubleword is multiplied
188	 * with zero to not contribute to the intermedate results.
189	 */
190
191	/* T1(x) = floor( R(x) / x^32 ) GF2MUL u */
192	VUPLLF	%v2,%v1
193	VGFMG	%v2,CONST_RU_POLY,%v2
194
195	/*
196	 * Compute the GF(2) product of the CRC polynomial in VO with T1(x) in
197	 * V2 and XOR the intermediate result, T2(x),  with the value in V1.
198	 * The final result is in the rightmost word of V2.
199	 */
200	VUPLLF	%v2,%v2
201	VGFMAG	%v2,CONST_CRC_POLY,%v2,%v1
202
203.Ldone:
204	VLGVF	%r2,%v2,3
205	br	%r14
206
207.previous
208