crc32_sse42.c

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    1 /*
    2  * Derived from crc32c.c version 1.1 by Mark Adler.
    3  *
    4  * Copyright (C) 2013 Mark Adler
    5  *
    6  * This software is provided 'as-is', without any express or implied warranty.
    7  * In no event will the author be held liable for any damages arising from the
    8  * use of this software.
    9  *
   10  * Permission is granted to anyone to use this software for any purpose,
   11  * including commercial applications, and to alter it and redistribute it
   12  * freely, subject to the following restrictions:
   13  *
   14  * 1. The origin of this software must not be misrepresented; you must not
   15  *    claim that you wrote the original software. If you use this software
   16  *    in a product, an acknowledgment in the product documentation would be
   17  *    appreciated but is not required.
   18  * 2. Altered source versions must be plainly marked as such, and must not be
   19  *    misrepresented as being the original software.
   20  * 3. This notice may not be removed or altered from any source distribution.
   21  *
   22  * Mark Adler
   23  * madler@alumni.caltech.edu
   24  */
   25 
   26 #include <sys/cdefs.h>
   27 __FBSDID("$FreeBSD$");
   28 
   29 /*
   30  * This file is compiled in userspace in order to run ATF unit tests.
   31  */
   32 #ifndef _KERNEL
   33 #include <stdint.h>
   34 #include <stdlib.h>
   35 #else
   36 #include <sys/param.h>
   37 #include <sys/kernel.h>
   38 #endif
   39 #include <sys/gsb_crc32.h>
   40 
   41 static __inline uint32_t
   42 _mm_crc32_u8(uint32_t x, uint8_t y)
   43 {
   44         /*
   45          * clang (at least 3.9.[0-1]) pessimizes "rm" (y) and "m" (y)
   46          * significantly and "r" (y) a lot by copying y to a different
   47          * local variable (on the stack or in a register), so only use
   48          * the latter.  This costs a register and an instruction but
   49          * not a uop.
   50          */
   51         __asm("crc32b %1,%0" : "+r" (x) : "r" (y));
   52         return (x);
   53 }
   54 
   55 #ifdef __amd64__
   56 static __inline uint64_t
   57 _mm_crc32_u64(uint64_t x, uint64_t y)
   58 {
   59         __asm("crc32q %1,%0" : "+r" (x) : "r" (y));
   60         return (x);
   61 }
   62 #else
   63 static __inline uint32_t
   64 _mm_crc32_u32(uint32_t x, uint32_t y)
   65 {
   66         __asm("crc32l %1,%0" : "+r" (x) : "r" (y));
   67         return (x);
   68 }
   69 #endif
   70 
   71 /* CRC-32C (iSCSI) polynomial in reversed bit order. */
   72 #define POLY    0x82f63b78
   73 
   74 /*
   75  * Block sizes for three-way parallel crc computation.  LONG and SHORT must
   76  * both be powers of two.
   77  */
   78 #define LONG    128
   79 #define SHORT   64
   80 
   81 /* 
   82  * Tables for updating a crc for LONG, 2 * LONG, SHORT and 2 * SHORT bytes
   83  * of value 0 later in the input stream, in the same way that the hardware
   84  * would, but in software without calculating intermediate steps.
   85  */
   86 static uint32_t crc32c_long[4][256];
   87 static uint32_t crc32c_2long[4][256];
   88 static uint32_t crc32c_short[4][256];
   89 static uint32_t crc32c_2short[4][256];
   90 
   91 /*
   92  * Multiply a matrix times a vector over the Galois field of two elements,
   93  * GF(2).  Each element is a bit in an unsigned integer.  mat must have at
   94  * least as many entries as the power of two for most significant one bit in
   95  * vec.
   96  */
   97 static inline uint32_t
   98 gf2_matrix_times(uint32_t *mat, uint32_t vec)
   99 {
  100         uint32_t sum;
  101 
  102         sum = 0;
  103         while (vec) {
  104                 if (vec & 1)
  105                         sum ^= *mat;
  106                 vec >>= 1;
  107                 mat++;
  108         }
  109         return (sum);
  110 }
  111 
  112 /*
  113  * Multiply a matrix by itself over GF(2).  Both mat and square must have 32
  114  * rows.
  115  */
  116 static inline void
  117 gf2_matrix_square(uint32_t *square, uint32_t *mat)
  118 {
  119         int n;
  120 
  121         for (n = 0; n < 32; n++)
  122                 square[n] = gf2_matrix_times(mat, mat[n]);
  123 }
  124 
  125 /*
  126  * Construct an operator to apply len zeros to a crc.  len must be a power of
  127  * two.  If len is not a power of two, then the result is the same as for the
  128  * largest power of two less than len.  The result for len == 0 is the same as
  129  * for len == 1.  A version of this routine could be easily written for any
  130  * len, but that is not needed for this application.
  131  */
  132 static void
  133 crc32c_zeros_op(uint32_t *even, size_t len)
  134 {
  135         uint32_t odd[32];       /* odd-power-of-two zeros operator */
  136         uint32_t row;
  137         int n;
  138 
  139         /* put operator for one zero bit in odd */
  140         odd[0] = POLY;              /* CRC-32C polynomial */
  141         row = 1;
  142         for (n = 1; n < 32; n++) {
  143                 odd[n] = row;
  144                 row <<= 1;
  145         }
  146 
  147         /* put operator for two zero bits in even */
  148         gf2_matrix_square(even, odd);
  149 
  150         /* put operator for four zero bits in odd */
  151         gf2_matrix_square(odd, even);
  152 
  153         /*
  154          * first square will put the operator for one zero byte (eight zero
  155          * bits), in even -- next square puts operator for two zero bytes in
  156          * odd, and so on, until len has been rotated down to zero
  157          */
  158         do {
  159                 gf2_matrix_square(even, odd);
  160                 len >>= 1;
  161                 if (len == 0)
  162                         return;
  163                 gf2_matrix_square(odd, even);
  164                 len >>= 1;
  165         } while (len);
  166 
  167         /* answer ended up in odd -- copy to even */
  168         for (n = 0; n < 32; n++)
  169                 even[n] = odd[n];
  170 }
  171 
  172 /*
  173  * Take a length and build four lookup tables for applying the zeros operator
  174  * for that length, byte-by-byte on the operand.
  175  */
  176 static void
  177 crc32c_zeros(uint32_t zeros[][256], size_t len)
  178 {
  179         uint32_t op[32];
  180         uint32_t n;
  181 
  182         crc32c_zeros_op(op, len);
  183         for (n = 0; n < 256; n++) {
  184                 zeros[0][n] = gf2_matrix_times(op, n);
  185                 zeros[1][n] = gf2_matrix_times(op, n << 8);
  186                 zeros[2][n] = gf2_matrix_times(op, n << 16);
  187                 zeros[3][n] = gf2_matrix_times(op, n << 24);
  188         }
  189 }
  190 
  191 /* Apply the zeros operator table to crc. */
  192 static inline uint32_t
  193 crc32c_shift(uint32_t zeros[][256], uint32_t crc)
  194 {
  195 
  196         return (zeros[0][crc & 0xff] ^ zeros[1][(crc >> 8) & 0xff] ^
  197             zeros[2][(crc >> 16) & 0xff] ^ zeros[3][crc >> 24]);
  198 }
  199 
  200 /* Initialize tables for shifting crcs. */
  201 static void
  202 #ifndef _KERNEL
  203 __attribute__((__constructor__))
  204 #endif
  205 crc32c_init_hw(void)
  206 {
  207         crc32c_zeros(crc32c_long, LONG);
  208         crc32c_zeros(crc32c_2long, 2 * LONG);
  209         crc32c_zeros(crc32c_short, SHORT);
  210         crc32c_zeros(crc32c_2short, 2 * SHORT);
  211 }
  212 #ifdef _KERNEL
  213 SYSINIT(crc32c_sse42, SI_SUB_LOCK, SI_ORDER_ANY, crc32c_init_hw, NULL);
  214 #endif
  215 
  216 /* Compute CRC-32C using the Intel hardware instruction. */
  217 uint32_t
  218 sse42_crc32c(uint32_t crc, const unsigned char *buf, unsigned len)
  219 {
  220 #ifdef __amd64__
  221         const size_t align = 8;
  222 #else
  223         const size_t align = 4;
  224 #endif
  225         const unsigned char *next, *end;
  226 #ifdef __amd64__
  227         uint64_t crc0, crc1, crc2;
  228 #else
  229         uint32_t crc0, crc1, crc2;
  230 #endif
  231 
  232         next = buf;
  233         crc0 = crc;
  234 
  235         /* Compute the crc to bring the data pointer to an aligned boundary. */
  236         while (len && ((uintptr_t)next & (align - 1)) != 0) {
  237                 crc0 = _mm_crc32_u8(crc0, *next);
  238                 next++;
  239                 len--;
  240         }
  241 
  242 #if LONG > SHORT
  243         /*
  244          * Compute the crc on sets of LONG*3 bytes, executing three independent
  245          * crc instructions, each on LONG bytes -- this is optimized for the
  246          * Nehalem, Westmere, Sandy Bridge, and Ivy Bridge architectures, which
  247          * have a throughput of one crc per cycle, but a latency of three
  248          * cycles.
  249          */
  250         crc = 0;
  251         while (len >= LONG * 3) {
  252                 crc1 = 0;
  253                 crc2 = 0;
  254                 end = next + LONG;
  255                 do {
  256 #ifdef __amd64__
  257                         crc0 = _mm_crc32_u64(crc0, *(const uint64_t *)next);
  258                         crc1 = _mm_crc32_u64(crc1,
  259                             *(const uint64_t *)(next + LONG));
  260                         crc2 = _mm_crc32_u64(crc2,
  261                             *(const uint64_t *)(next + (LONG * 2)));
  262 #else
  263                         crc0 = _mm_crc32_u32(crc0, *(const uint32_t *)next);
  264                         crc1 = _mm_crc32_u32(crc1,
  265                             *(const uint32_t *)(next + LONG));
  266                         crc2 = _mm_crc32_u32(crc2,
  267                             *(const uint32_t *)(next + (LONG * 2)));
  268 #endif
  269                         next += align;
  270                 } while (next < end);
  271                 /*-
  272                  * Update the crc.  Try to do it in parallel with the inner
  273                  * loop.  'crc' is used to accumulate crc0 and crc1
  274                  * produced by the inner loop so that the next iteration
  275                  * of the loop doesn't depend on anything except crc2.
  276                  *
  277                  * The full expression for the update is:
  278                  *     crc = S*S*S*crc + S*S*crc0 + S*crc1
  279                  * where the terms are polynomials modulo the CRC polynomial.
  280                  * We regroup this subtly as:
  281                  *     crc = S*S * (S*crc + crc0) + S*crc1.
  282                  * This has an extra dependency which reduces possible
  283                  * parallelism for the expression, but it turns out to be
  284                  * best to intentionally delay evaluation of this expression
  285                  * so that it competes less with the inner loop.
  286                  *
  287                  * We also intentionally reduce parallelism by feedng back
  288                  * crc2 to the inner loop as crc0 instead of accumulating
  289                  * it in crc.  This synchronizes the loop with crc update.
  290                  * CPU and/or compiler schedulers produced bad order without
  291                  * this.
  292                  *
  293                  * Shifts take about 12 cycles each, so 3 here with 2
  294                  * parallelizable take about 24 cycles and the crc update
  295                  * takes slightly longer.  8 dependent crc32 instructions
  296                  * can run in 24 cycles, so the 3-way blocking is worse
  297                  * than useless for sizes less than 8 * <word size> = 64
  298                  * on amd64.  In practice, SHORT = 32 confirms these
  299                  * timing calculations by giving a small improvement
  300                  * starting at size 96.  Then the inner loop takes about
  301                  * 12 cycles and the crc update about 24, but these are
  302                  * partly in parallel so the total time is less than the
  303                  * 36 cycles that 12 dependent crc32 instructions would
  304                  * take.
  305                  *
  306                  * To have a chance of completely hiding the overhead for
  307                  * the crc update, the inner loop must take considerably
  308                  * longer than 24 cycles.  LONG = 64 makes the inner loop
  309                  * take about 24 cycles, so is not quite large enough.
  310                  * LONG = 128 works OK.  Unhideable overheads are about
  311                  * 12 cycles per inner loop.  All assuming timing like
  312                  * Haswell.
  313                  */
  314                 crc = crc32c_shift(crc32c_long, crc) ^ crc0;
  315                 crc1 = crc32c_shift(crc32c_long, crc1);
  316                 crc = crc32c_shift(crc32c_2long, crc) ^ crc1;
  317                 crc0 = crc2;
  318                 next += LONG * 2;
  319                 len -= LONG * 3;
  320         }
  321         crc0 ^= crc;
  322 #endif /* LONG > SHORT */
  323 
  324         /*
  325          * Do the same thing, but now on SHORT*3 blocks for the remaining data
  326          * less than a LONG*3 block
  327          */
  328         crc = 0;
  329         while (len >= SHORT * 3) {
  330                 crc1 = 0;
  331                 crc2 = 0;
  332                 end = next + SHORT;
  333                 do {
  334 #ifdef __amd64__
  335                         crc0 = _mm_crc32_u64(crc0, *(const uint64_t *)next);
  336                         crc1 = _mm_crc32_u64(crc1,
  337                             *(const uint64_t *)(next + SHORT));
  338                         crc2 = _mm_crc32_u64(crc2,
  339                             *(const uint64_t *)(next + (SHORT * 2)));
  340 #else
  341                         crc0 = _mm_crc32_u32(crc0, *(const uint32_t *)next);
  342                         crc1 = _mm_crc32_u32(crc1,
  343                             *(const uint32_t *)(next + SHORT));
  344                         crc2 = _mm_crc32_u32(crc2,
  345                             *(const uint32_t *)(next + (SHORT * 2)));
  346 #endif
  347                         next += align;
  348                 } while (next < end);
  349                 crc = crc32c_shift(crc32c_short, crc) ^ crc0;
  350                 crc1 = crc32c_shift(crc32c_short, crc1);
  351                 crc = crc32c_shift(crc32c_2short, crc) ^ crc1;
  352                 crc0 = crc2;
  353                 next += SHORT * 2;
  354                 len -= SHORT * 3;
  355         }
  356         crc0 ^= crc;
  357 
  358         /* Compute the crc on the remaining bytes at native word size. */
  359         end = next + (len - (len & (align - 1)));
  360         while (next < end) {
  361 #ifdef __amd64__
  362                 crc0 = _mm_crc32_u64(crc0, *(const uint64_t *)next);
  363 #else
  364                 crc0 = _mm_crc32_u32(crc0, *(const uint32_t *)next);
  365 #endif
  366                 next += align;
  367         }
  368         len &= (align - 1);
  369 
  370         /* Compute the crc for any trailing bytes. */
  371         while (len) {
  372                 crc0 = _mm_crc32_u8(crc0, *next);
  373                 next++;
  374                 len--;
  375         }
  376 
  377         return ((uint32_t)crc0);
  378 }
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FreeBSD/Linux Kernel Cross Reference sys/libkern/x86/crc32_sse42.c

FreeBSD/Linux Kernel Cross Reference
sys/libkern/x86/crc32_sse42.c
