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Diffstat (limited to 'module/zfs/fletcher.c')
| -rw-r--r-- | module/zfs/fletcher.c | 245 |
1 files changed, 0 insertions, 245 deletions
diff --git a/module/zfs/fletcher.c b/module/zfs/fletcher.c deleted file mode 100644 index 54247d724..000000000 --- a/module/zfs/fletcher.c +++ /dev/null @@ -1,245 +0,0 @@ -/* - * CDDL HEADER START - * - * The contents of this file are subject to the terms of the - * Common Development and Distribution License (the "License"). - * You may not use this file except in compliance with the License. - * - * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE - * or http://www.opensolaris.org/os/licensing. - * See the License for the specific language governing permissions - * and limitations under the License. - * - * When distributing Covered Code, include this CDDL HEADER in each - * file and include the License file at usr/src/OPENSOLARIS.LICENSE. - * If applicable, add the following below this CDDL HEADER, with the - * fields enclosed by brackets "[]" replaced with your own identifying - * information: Portions Copyright [yyyy] [name of copyright owner] - * - * CDDL HEADER END - */ -/* - * Copyright 2009 Sun Microsystems, Inc. All rights reserved. - * Use is subject to license terms. - */ - -/* - * Fletcher Checksums - * ------------------ - * - * ZFS's 2nd and 4th order Fletcher checksums are defined by the following - * recurrence relations: - * - * a = a + f - * i i-1 i-1 - * - * b = b + a - * i i-1 i - * - * c = c + b (fletcher-4 only) - * i i-1 i - * - * d = d + c (fletcher-4 only) - * i i-1 i - * - * Where - * a_0 = b_0 = c_0 = d_0 = 0 - * and - * f_0 .. f_(n-1) are the input data. - * - * Using standard techniques, these translate into the following series: - * - * __n_ __n_ - * \ | \ | - * a = > f b = > i * f - * n /___| n - i n /___| n - i - * i = 1 i = 1 - * - * - * __n_ __n_ - * \ | i*(i+1) \ | i*(i+1)*(i+2) - * c = > ------- f d = > ------------- f - * n /___| 2 n - i n /___| 6 n - i - * i = 1 i = 1 - * - * For fletcher-2, the f_is are 64-bit, and [ab]_i are 64-bit accumulators. - * Since the additions are done mod (2^64), errors in the high bits may not - * be noticed. For this reason, fletcher-2 is deprecated. - * - * For fletcher-4, the f_is are 32-bit, and [abcd]_i are 64-bit accumulators. - * A conservative estimate of how big the buffer can get before we overflow - * can be estimated using f_i = 0xffffffff for all i: - * - * % bc - * f=2^32-1;d=0; for (i = 1; d<2^64; i++) { d += f*i*(i+1)*(i+2)/6 }; (i-1)*4 - * 2264 - * quit - * % - * - * So blocks of up to 2k will not overflow. Our largest block size is - * 128k, which has 32k 4-byte words, so we can compute the largest possible - * accumulators, then divide by 2^64 to figure the max amount of overflow: - * - * % bc - * a=b=c=d=0; f=2^32-1; for (i=1; i<=32*1024; i++) { a+=f; b+=a; c+=b; d+=c } - * a/2^64;b/2^64;c/2^64;d/2^64 - * 0 - * 0 - * 1365 - * 11186858 - * quit - * % - * - * So a and b cannot overflow. To make sure each bit of input has some - * effect on the contents of c and d, we can look at what the factors of - * the coefficients in the equations for c_n and d_n are. The number of 2s - * in the factors determines the lowest set bit in the multiplier. Running - * through the cases for n*(n+1)/2 reveals that the highest power of 2 is - * 2^14, and for n*(n+1)*(n+2)/6 it is 2^15. So while some data may overflow - * the 64-bit accumulators, every bit of every f_i effects every accumulator, - * even for 128k blocks. - * - * If we wanted to make a stronger version of fletcher4 (fletcher4c?), - * we could do our calculations mod (2^32 - 1) by adding in the carries - * periodically, and store the number of carries in the top 32-bits. - * - * -------------------- - * Checksum Performance - * -------------------- - * - * There are two interesting components to checksum performance: cached and - * uncached performance. With cached data, fletcher-2 is about four times - * faster than fletcher-4. With uncached data, the performance difference is - * negligible, since the cost of a cache fill dominates the processing time. - * Even though fletcher-4 is slower than fletcher-2, it is still a pretty - * efficient pass over the data. - * - * In normal operation, the data which is being checksummed is in a buffer - * which has been filled either by: - * - * 1. a compression step, which will be mostly cached, or - * 2. a bcopy() or copyin(), which will be uncached (because the - * copy is cache-bypassing). - * - * For both cached and uncached data, both fletcher checksums are much faster - * than sha-256, and slower than 'off', which doesn't touch the data at all. - */ - -#include <sys/types.h> -#include <sys/sysmacros.h> -#include <sys/byteorder.h> -#include <sys/spa.h> - -void -fletcher_2_native(const void *buf, uint64_t size, zio_cksum_t *zcp) -{ - const uint64_t *ip = buf; - const uint64_t *ipend = ip + (size / sizeof (uint64_t)); - uint64_t a0, b0, a1, b1; - - for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { - a0 += ip[0]; - a1 += ip[1]; - b0 += a0; - b1 += a1; - } - - ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); -} - -void -fletcher_2_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) -{ - const uint64_t *ip = buf; - const uint64_t *ipend = ip + (size / sizeof (uint64_t)); - uint64_t a0, b0, a1, b1; - - for (a0 = b0 = a1 = b1 = 0; ip < ipend; ip += 2) { - a0 += BSWAP_64(ip[0]); - a1 += BSWAP_64(ip[1]); - b0 += a0; - b1 += a1; - } - - ZIO_SET_CHECKSUM(zcp, a0, a1, b0, b1); -} - -void -fletcher_4_native(const void *buf, uint64_t size, zio_cksum_t *zcp) -{ - const uint32_t *ip = buf; - const uint32_t *ipend = ip + (size / sizeof (uint32_t)); - uint64_t a, b, c, d; - - for (a = b = c = d = 0; ip < ipend; ip++) { - a += ip[0]; - b += a; - c += b; - d += c; - } - - ZIO_SET_CHECKSUM(zcp, a, b, c, d); -} - -void -fletcher_4_byteswap(const void *buf, uint64_t size, zio_cksum_t *zcp) -{ - const uint32_t *ip = buf; - const uint32_t *ipend = ip + (size / sizeof (uint32_t)); - uint64_t a, b, c, d; - - for (a = b = c = d = 0; ip < ipend; ip++) { - a += BSWAP_32(ip[0]); - b += a; - c += b; - d += c; - } - - ZIO_SET_CHECKSUM(zcp, a, b, c, d); -} - -void -fletcher_4_incremental_native(const void *buf, uint64_t size, - zio_cksum_t *zcp) -{ - const uint32_t *ip = buf; - const uint32_t *ipend = ip + (size / sizeof (uint32_t)); - uint64_t a, b, c, d; - - a = zcp->zc_word[0]; - b = zcp->zc_word[1]; - c = zcp->zc_word[2]; - d = zcp->zc_word[3]; - - for (; ip < ipend; ip++) { - a += ip[0]; - b += a; - c += b; - d += c; - } - - ZIO_SET_CHECKSUM(zcp, a, b, c, d); -} - -void -fletcher_4_incremental_byteswap(const void *buf, uint64_t size, - zio_cksum_t *zcp) -{ - const uint32_t *ip = buf; - const uint32_t *ipend = ip + (size / sizeof (uint32_t)); - uint64_t a, b, c, d; - - a = zcp->zc_word[0]; - b = zcp->zc_word[1]; - c = zcp->zc_word[2]; - d = zcp->zc_word[3]; - - for (; ip < ipend; ip++) { - a += BSWAP_32(ip[0]); - b += a; - c += b; - d += c; - } - - ZIO_SET_CHECKSUM(zcp, a, b, c, d); -} |