Skip to content

Commit

Permalink
liblzma: Moved CLMUL CRC logic to crc_common.h.
Browse files Browse the repository at this point in the history 
crc64_fast.c was updated to use the code from crc_common.h instead.
  • Loading branch information
@hansjans162 @JiaT75
hansjans162 authored and JiaT75 committed Oct 13, 2023
1 parent 233885a commit 93e6fb0
Show file tree
Hide file tree
Showing 2 changed files with 240 additions and 247 deletions.
257 changes: 12 additions & 245 deletions src/liblzma/check/crc64_fast.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,9 @@
///
/// crc64_clmul uses 32/64-bit x86 SSSE3, SSE4.1, and CLMUL instructions.
/// It was derived from
/// https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-generic-polynomials-pclmulqdq-paper.pdf
/// https://www.researchgate.net/publication/263424619_Fast_CRC_computation
/// and the public domain code from https://github.com/rawrunprotected/crc
/// (URLs were checked on 2022-11-07).
/// (URLs were checked on 2023-09-29).
///
/// FIXME: Builds for 32-bit x86 use crc64_x86.S by default instead
/// of this file and thus CLMUL version isn't available on 32-bit x86
Expand All @@ -29,56 +29,14 @@
///////////////////////////////////////////////////////////////////////////////

#include "check.h"

#undef CRC_GENERIC
#undef CRC_CLMUL
#undef CRC_USE_GENERIC_FOR_SMALL_INPUTS

// If CLMUL cannot be used then only the generic slice-by-four is built.
#if !defined(HAVE_USABLE_CLMUL)
# define CRC_GENERIC 1

// If CLMUL is allowed unconditionally in the compiler options then the
// generic version can be omitted. Note that this doesn't work with MSVC
// as I don't know how to detect the features here.
//
// NOTE: Keep this this in sync with crc64_table.c.
#elif (defined(__SSSE3__) && defined(__SSE4_1__) && defined(__PCLMUL__)) \
|| (defined(__e2k__) && __iset__ >= 6)
# define CRC_CLMUL 1

// Otherwise build both and detect at runtime which version to use.
#else
# define CRC_GENERIC 1
# define CRC_CLMUL 1

/*
// The generic code is much faster with 1-8-byte inputs and has
// similar performance up to 16 bytes at least in microbenchmarks
// (it depends on input buffer alignment too). If both versions are
// built, this #define will use the generic version for inputs up to
// 16 bytes and CLMUL for bigger inputs. It saves a little in code
// size since the special cases for 0-16-byte inputs will be omitted
// from the CLMUL code.
# define CRC_USE_GENERIC_FOR_SMALL_INPUTS 1
*/

# if defined(_MSC_VER)
# include <intrin.h>
# elif defined(HAVE_CPUID_H)
# include <cpuid.h>
# endif
#endif

#include "crc_common.h"

/////////////////////////////////
// Generic slice-by-four CRC64 //
/////////////////////////////////

#ifdef CRC_GENERIC

#include "crc_common.h"


#ifdef WORDS_BIGENDIAN
# define A1(x) ((x) >> 56)
Expand Down Expand Up @@ -173,17 +131,6 @@ calc_hi(uint64_t poly, uint64_t a)
*/


#define MASK_L(in, mask, r) \
r = _mm_shuffle_epi8(in, mask)

#define MASK_H(in, mask, r) \
r = _mm_shuffle_epi8(in, _mm_xor_si128(mask, vsign))

#define MASK_LH(in, mask, low, high) \
MASK_L(in, mask, low); \
MASK_H(in, mask, high)


// MSVC (VS2015 - VS2022) produces bad 32-bit x86 code from the CLMUL CRC
// code when optimizations are enabled (release build). According to the bug
// report, the ebx register is corrupted and the calculated result is wrong.
Expand All @@ -206,14 +153,6 @@ calc_hi(uint64_t poly, uint64_t a)
#if (defined(__GNUC__) || defined(__clang__)) && !defined(__EDG__)
__attribute__((__target__("ssse3,sse4.1,pclmul")))
#endif
// The intrinsics use 16-byte-aligned reads from buf, thus they may read
// up to 15 bytes before or after the buffer (depending on the alignment
// of the buf argument). The values of the extra bytes are ignored.
// This unavoidably trips -fsanitize=address so address sanitizier has
// to be disabled for this function.
#if lzma_has_attribute(__no_sanitize_address__)
__attribute__((__no_sanitize_address__))
#endif
static uint64_t
crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
{
Expand All @@ -237,150 +176,24 @@ crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
const uint64_t mu = 0x9c3e466c172963d5; // (calc_lo(poly) << 1) | 1
const uint64_t k2 = 0xdabe95afc7875f40; // calc_hi(poly, 1)
const uint64_t k1 = 0xe05dd497ca393ae4; // calc_hi(poly, k2)
const __m128i vfold0 = _mm_set_epi64x(p, mu);
const __m128i vfold1 = _mm_set_epi64x(k2, k1);

// Create a vector with 8-bit values 0 to 15. This is used to
// construct control masks for _mm_blendv_epi8 and _mm_shuffle_epi8.
const __m128i vramp = _mm_setr_epi32(
0x03020100, 0x07060504, 0x0b0a0908, 0x0f0e0d0c);
const __m128i vfold8 = _mm_set_epi64x(p, mu);
const __m128i vfold16 = _mm_set_epi64x(k2, k1);

// This is used to inverse the control mask of _mm_shuffle_epi8
// so that bytes that wouldn't be picked with the original mask
// will be picked and vice versa.
const __m128i vsign = _mm_set1_epi8(0x80);

// Memory addresses A to D and the distances between them:
//
// A B C D
// [skip_start][size][skip_end]
// [ size2 ]
//
// A and D are 16-byte aligned. B and C are 1-byte aligned.
// skip_start and skip_end are 0-15 bytes. size is at least 1 byte.
//
// A = aligned_buf will initially point to this address.
// B = The address pointed by the caller-supplied buf.
// C = buf + size == aligned_buf + size2
// D = buf + size + skip_end == aligned_buf + size2 + skip_end
const size_t skip_start = (size_t)((uintptr_t)buf & 15);
const size_t skip_end = (size_t)((0U - (uintptr_t)(buf + size)) & 15);
const __m128i *aligned_buf = (const __m128i *)(
(uintptr_t)buf & ~(uintptr_t)15);

// If size2 <= 16 then the whole input fits into a single 16-byte
// vector. If size2 > 16 then at least two 16-byte vectors must
// be processed. If size2 > 16 && size <= 16 then there is only
// one 16-byte vector's worth of input but it is unaligned in memory.
//
// NOTE: There is no integer overflow here if the arguments are valid.
// If this overflowed, buf + size would too.
size_t size2 = skip_start + size;

// Masks to be used with _mm_blendv_epi8 and _mm_shuffle_epi8:
// The first skip_start or skip_end bytes in the vectors will have
// the high bit (0x80) set. _mm_blendv_epi8 and _mm_shuffle_epi8
// will produce zeros for these positions. (Bitwise-xor of these
// masks with vsign will produce the opposite behavior.)
const __m128i mask_start
= _mm_sub_epi8(vramp, _mm_set1_epi8(skip_start));
const __m128i mask_end = _mm_sub_epi8(vramp, _mm_set1_epi8(skip_end));

// Get the first 1-16 bytes into data0. If loading less than 16 bytes,
// the bytes are loaded to the high bits of the vector and the least
// significant positions are filled with zeros.
const __m128i data0 = _mm_blendv_epi8(_mm_load_si128(aligned_buf),
_mm_setzero_si128(), mask_start);
++aligned_buf;
__m128i v0, v1, v2;

#if defined(__i386__) || defined(_M_IX86)
const __m128i initial_crc = _mm_set_epi64x(0, ~crc);
crc_simd_body(buf, size, &v0, &v1, vfold16, _mm_set_epi64x(0, ~crc));
#else
// GCC and Clang would produce good code with _mm_set_epi64x
// but MSVC needs _mm_cvtsi64_si128 on x86-64.
const __m128i initial_crc = _mm_cvtsi64_si128(~crc);
#endif

__m128i v0, v1, v2, v3;

#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
if (size <= 16) {
// Right-shift initial_crc by 1-16 bytes based on "size"
// and store the result in v1 (high bytes) and v0 (low bytes).
//
// NOTE: The highest 8 bytes of initial_crc are zeros so
// v1 will be filled with zeros if size >= 8. The highest 8
// bytes of v1 will always become zeros.
//
// [ v1 ][ v0 ]
// [ initial_crc ] size == 1
// [ initial_crc ] size == 2
// [ initial_crc ] size == 15
// [ initial_crc ] size == 16 (all in v0)
const __m128i mask_low = _mm_add_epi8(
vramp, _mm_set1_epi8(size - 16));
MASK_LH(initial_crc, mask_low, v0, v1);

if (size2 <= 16) {
// There are 1-16 bytes of input and it is all
// in data0. Copy the input bytes to v3. If there
// are fewer than 16 bytes, the low bytes in v3
// will be filled with zeros. That is, the input
// bytes are stored to the same position as
// (part of) initial_crc is in v0.
MASK_L(data0, mask_end, v3);
} else {
// There are 2-16 bytes of input but not all bytes
// are in data0.
const __m128i data1 = _mm_load_si128(aligned_buf);

// Collect the 2-16 input bytes from data0 and data1
// to v2 and v3, and bitwise-xor them with the
// low bits of initial_crc in v0. Note that the
// the second xor is below this else-block as it
// is shared with the other branch.
MASK_H(data0, mask_end, v2);
MASK_L(data1, mask_end, v3);
v0 = _mm_xor_si128(v0, v2);
}

v0 = _mm_xor_si128(v0, v3);
v1 = _mm_alignr_epi8(v1, v0, 8);
} else
crc_simd_body(buf, size, &v0, &v1, vfold16, _mm_cvtsi64_si128(~crc));
#endif
{
const __m128i data1 = _mm_load_si128(aligned_buf);
MASK_LH(initial_crc, mask_start, v0, v1);
v0 = _mm_xor_si128(v0, data0);
v1 = _mm_xor_si128(v1, data1);

#define FOLD \
v1 = _mm_xor_si128(v1, _mm_clmulepi64_si128(v0, vfold1, 0x00)); \
v0 = _mm_xor_si128(v1, _mm_clmulepi64_si128(v0, vfold1, 0x11));

while (size2 > 32) {
++aligned_buf;
size2 -= 16;
FOLD
v1 = _mm_load_si128(aligned_buf);
}

if (size2 < 32) {
MASK_H(v0, mask_end, v2);
MASK_L(v0, mask_end, v0);
MASK_L(v1, mask_end, v3);
v1 = _mm_or_si128(v2, v3);
}

FOLD
v1 = _mm_srli_si128(v0, 8);
#undef FOLD
}

v1 = _mm_xor_si128(_mm_clmulepi64_si128(v0, vfold1, 0x10), v1);
v0 = _mm_clmulepi64_si128(v1, vfold0, 0x00);
v2 = _mm_clmulepi64_si128(v0, vfold0, 0x10);
v0 = _mm_xor_si128(_mm_xor_si128(v2, _mm_slli_si128(v0, 8)), v1);
v1 = _mm_xor_si128(_mm_clmulepi64_si128(v0, vfold16, 0x10), v1);
v0 = _mm_clmulepi64_si128(v1, vfold8, 0x00);
v2 = _mm_clmulepi64_si128(v0, vfold8, 0x10);
v0 = _mm_xor_si128(_mm_xor_si128(v1, _mm_slli_si128(v0, 8)), v2);

#if defined(__i386__) || defined(_M_IX86)
return ~(((uint64_t)(uint32_t)_mm_extract_epi32(v0, 3) << 32) |
Expand All @@ -399,53 +212,7 @@ crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
#endif
#endif


////////////////////////
// Detect CPU support //
////////////////////////

#if defined(CRC_GENERIC) && defined(CRC_CLMUL)
static inline bool
is_clmul_supported(void)
{
int success = 1;
uint32_t r[4]; // eax, ebx, ecx, edx

#if defined(_MSC_VER)
// This needs <intrin.h> with MSVC. ICC has it as a built-in
// on all platforms.
__cpuid(r, 1);
#elif defined(HAVE_CPUID_H)
// Compared to just using __asm__ to run CPUID, this also checks
// that CPUID is supported and saves and restores ebx as that is
// needed with GCC < 5 with position-independent code (PIC).
success = __get_cpuid(1, &r[0], &r[1], &r[2], &r[3]);
#else
// Just a fallback that shouldn't be needed.
__asm__("cpuid\n\t"
: "=a"(r[0]), "=b"(r[1]), "=c"(r[2]), "=d"(r[3])
: "a"(1), "c"(0));
#endif

// Returns true if these are supported:
// CLMUL (bit 1 in ecx)
// SSSE3 (bit 9 in ecx)
// SSE4.1 (bit 19 in ecx)
const uint32_t ecx_mask = (1 << 1) | (1 << 9) | (1 << 19);
return success && (r[2] & ecx_mask) == ecx_mask;

// Alternative methods that weren't used:
// - ICC's _may_i_use_cpu_feature: the other methods should work too.
// - GCC >= 6 / Clang / ICX __builtin_cpu_supports("pclmul")
//
// CPUID decding is needed with MSVC anyway and older GCC. This keeps
// the feature checks in the build system simpler too. The nice thing
// about __builtin_cpu_supports would be that it generates very short
// code as is it only reads a variable set at startup but a few bytes
// doesn't matter here.
}


typedef uint64_t (*crc64_func_type)(
const uint8_t *buf, size_t size, uint64_t crc);

Expand Down
Loading

0 comments on commit 93e6fb0

Please sign in to comment.