1 /* Adler32 for POWER8 using VSX instructions.
2 * Copyright (C) 2020 IBM Corporation
3 * Author: Rogerio Alves <rcardoso@linux.ibm.com>
4 * For conditions of distribution and use, see copyright notice in zlib.h
5 *
6 * Calculate adler32 checksum for 16 bytes at once using POWER8+ VSX (vector)
7 * instructions.
8 *
9 * If adler32 do 1 byte at time on the first iteration s1 is s1_0 (_n means
10 * iteration n) is the initial value of adler - at start _0 is 1 unless
11 * adler initial value is different than 1. So s1_1 = s1_0 + c[0] after
12 * the first calculation. For the iteration s1_2 = s1_1 + c[1] and so on.
13 * Hence, for iteration N, s1_N = s1_(N-1) + c[N] is the value of s1 on
14 * after iteration N.
15 *
16 * Therefore, for s2 and iteration N, s2_N = s2_0 + N*s1_N + N*c[0] +
17 * N-1*c[1] + ... + c[N]
18 *
19 * In a more general way:
20 *
21 * s1_N = s1_0 + sum(i=1 to N)c[i]
22 * s2_N = s2_0 + N*s1 + sum (i=1 to N)(N-i+1)*c[i]
23 *
24 * Where s1_N, s2_N are the values for s1, s2 after N iterations. So if we
25 * can process N-bit at time we can do this at once.
26 *
27 * Since VSX can support 16-bit vector instructions, we can process
28 * 16-bit at time using N = 16 we have:
29 *
30 * s1 = s1_16 = s1_(16-1) + c[16] = s1_0 + sum(i=1 to 16)c[i]
31 * s2 = s2_16 = s2_0 + 16*s1 + sum(i=1 to 16)(16-i+1)*c[i]
32 *
33 * After the first iteration we calculate the adler32 checksum for 16 bytes.
34 *
35 * For more background about adler32 please check the RFC:
36 * https://www.ietf.org/rfc/rfc1950.txt
37 */
38
39 #ifdef POWER8_VSX_ADLER32
40
41 #include <altivec.h>
42 #include "zbuild.h"
43 #include "adler32_p.h"
44
45 /* Vector across sum unsigned int (saturate). */
vec_sumsu(vector unsigned int __a,vector unsigned int __b)46 static inline vector unsigned int vec_sumsu(vector unsigned int __a, vector unsigned int __b) {
47 __b = vec_sld(__a, __a, 8);
48 __b = vec_add(__b, __a);
49 __a = vec_sld(__b, __b, 4);
50 __a = vec_add(__a, __b);
51
52 return __a;
53 }
54
adler32_power8(uint32_t adler,const unsigned char * buf,size_t len)55 uint32_t adler32_power8(uint32_t adler, const unsigned char* buf, size_t len) {
56 uint32_t s1 = adler & 0xffff;
57 uint32_t s2 = (adler >> 16) & 0xffff;
58
59 /* in case user likes doing a byte at a time, keep it fast */
60 if (UNLIKELY(len == 1))
61 return adler32_len_1(s1, buf, s2);
62
63 /* If buffer is empty or len=0 we need to return adler initial value. */
64 if (UNLIKELY(buf == NULL))
65 return 1;
66
67 /* This is faster than VSX code for len < 64. */
68 if (len < 64)
69 return adler32_len_64(s1, buf, len, s2);
70
71 /* Use POWER VSX instructions for len >= 64. */
72 const vector unsigned int v_zeros = { 0 };
73 const vector unsigned char v_mul = {16, 15, 14, 13, 12, 11, 10, 9, 8, 7,
74 6, 5, 4, 3, 2, 1};
75 const vector unsigned char vsh = vec_splat_u8(4);
76 const vector unsigned int vmask = {0xffffffff, 0x0, 0x0, 0x0};
77 vector unsigned int vs1 = { 0 };
78 vector unsigned int vs2 = { 0 };
79 vector unsigned int vs1_save = { 0 };
80 vector unsigned int vsum1, vsum2;
81 vector unsigned char vbuf;
82 int n;
83
84 vs1[0] = s1;
85 vs2[0] = s2;
86
87 /* Do length bigger than NMAX in blocks of NMAX size. */
88 while (len >= NMAX) {
89 len -= NMAX;
90 n = NMAX / 16;
91 do {
92 vbuf = vec_xl(0, (unsigned char *) buf);
93 vsum1 = vec_sum4s(vbuf, v_zeros); /* sum(i=1 to 16) buf[i]. */
94 /* sum(i=1 to 16) buf[i]*(16-i+1). */
95 vsum2 = vec_msum(vbuf, v_mul, v_zeros);
96 /* Save vs1. */
97 vs1_save = vec_add(vs1_save, vs1);
98 /* Accumulate the sums. */
99 vs1 = vec_add(vsum1, vs1);
100 vs2 = vec_add(vsum2, vs2);
101
102 buf += 16;
103 } while (--n);
104 /* Once each block of NMAX size. */
105 vs1 = vec_sumsu(vs1, vsum1);
106 vs1_save = vec_sll(vs1_save, vsh); /* 16*vs1_save. */
107 vs2 = vec_add(vs1_save, vs2);
108 vs2 = vec_sumsu(vs2, vsum2);
109
110 /* vs1[0] = (s1_i + sum(i=1 to 16)buf[i]) mod 65521. */
111 vs1[0] = vs1[0] % BASE;
112 /* vs2[0] = s2_i + 16*s1_save +
113 sum(i=1 to 16)(16-i+1)*buf[i] mod 65521. */
114 vs2[0] = vs2[0] % BASE;
115
116 vs1 = vec_and(vs1, vmask);
117 vs2 = vec_and(vs2, vmask);
118 vs1_save = v_zeros;
119 }
120
121 /* len is less than NMAX one modulo is needed. */
122 if (len >= 16) {
123 while (len >= 16) {
124 len -= 16;
125
126 vbuf = vec_xl(0, (unsigned char *) buf);
127
128 vsum1 = vec_sum4s(vbuf, v_zeros); /* sum(i=1 to 16) buf[i]. */
129 /* sum(i=1 to 16) buf[i]*(16-i+1). */
130 vsum2 = vec_msum(vbuf, v_mul, v_zeros);
131 /* Save vs1. */
132 vs1_save = vec_add(vs1_save, vs1);
133 /* Accumulate the sums. */
134 vs1 = vec_add(vsum1, vs1);
135 vs2 = vec_add(vsum2, vs2);
136
137 buf += 16;
138 }
139 /* Since the size will be always less than NMAX we do this once. */
140 vs1 = vec_sumsu(vs1, vsum1);
141 vs1_save = vec_sll(vs1_save, vsh); /* 16*vs1_save. */
142 vs2 = vec_add(vs1_save, vs2);
143 vs2 = vec_sumsu(vs2, vsum2);
144 }
145 /* Copy result back to s1, s2 (mod 65521). */
146 s1 = vs1[0] % BASE;
147 s2 = vs2[0] % BASE;
148
149 /* Process tail (len < 16). */
150 return adler32_len_16(s1, buf, len, s2);
151 }
152
153 #endif /* POWER8_VSX_ADLER32 */
154