liblzma: Fix a typo in a comment

[xz/debian.git] / src / liblzma / check / crc_x86_clmul.h

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \file       crc_x86_clmul.h
/// \brief      CRC32 and CRC64 implementations using CLMUL instructions.
///
/// The CRC32 and CRC64 implementations use 32/64-bit x86 SSSE3, SSE4.1, and
/// CLMUL instructions. This is compatible with Elbrus 2000 (E2K) too.
///
/// They were derived from
/// https://www.researchgate.net/publication/263424619_Fast_CRC_computation
/// and the public domain code from https://github.com/rawrunprotected/crc
/// (URLs were checked on 2023-10-14).
///
/// While this file has both CRC32 and CRC64 implementations, only one
/// should be built at a time to ensure that crc_simd_body() is inlined
/// even with compilers with which lzma_always_inline expands to plain inline.
/// The version to build is selected by defining BUILDING_CRC32_CLMUL or
/// BUILDING_CRC64_CLMUL before including this file.
///
/// FIXME: Builds for 32-bit x86 use the assembly .S files by default
/// unless configured with --disable-assembler. Even then the lookup table
/// isn't omitted in crc64_table.c since it doesn't know that assembly
/// code has been disabled.
//
//  Authors:    Ilya Kurdyukov
//              Hans Jansen
//              Lasse Collin
//              Jia Tan
//
///////////////////////////////////////////////////////////////////////////////

// This file must not be included more than once.
#ifdef LZMA_CRC_X86_CLMUL_H
#       error crc_x86_clmul.h was included twice.
#endif
#define LZMA_CRC_X86_CLMUL_H

#include <immintrin.h>

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


// EDG-based compilers (Intel's classic compiler and compiler for E2K) can
// define __GNUC__ but the attribute must not be used with them.
// The new Clang-based ICX needs the attribute.
//
// NOTE: Build systems check for this too, keep them in sync with this.
#if (defined(__GNUC__) || defined(__clang__)) && !defined(__EDG__)
#       define crc_attr_target \
                __attribute__((__target__("ssse3,sse4.1,pclmul")))
#else
#       define crc_attr_target
#endif


#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)


crc_attr_target
crc_attr_no_sanitize_address
static lzma_always_inline void
crc_simd_body(const uint8_t *buf, const size_t size, __m128i *v0, __m128i *v1,
                const __m128i vfold16, const __m128i initial_crc)
{
        // 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);

        // 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.
        const 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((char)skip_start));
        const __m128i mask_end
                        = _mm_sub_epi8(vramp, _mm_set1_epi8((char)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 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((char)(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
#endif
        {
                // There is more than 16 bytes of input.
                const __m128i data1 = _mm_load_si128(aligned_buf);
                const __m128i *end = (const __m128i*)(
                                (const char *)aligned_buf - 16 + size2);
                aligned_buf++;

                MASK_LH(initial_crc, mask_start, *v0, *v1);
                *v0 = _mm_xor_si128(*v0, data0);
                *v1 = _mm_xor_si128(*v1, data1);

                while (aligned_buf < end) {
                        *v1 = _mm_xor_si128(*v1, _mm_clmulepi64_si128(
                                        *v0, vfold16, 0x00));
                        *v0 = _mm_xor_si128(*v1, _mm_clmulepi64_si128(
                                        *v0, vfold16, 0x11));
                        *v1 = _mm_load_si128(aligned_buf++);
                }

                if (aligned_buf != end) {
                        MASK_H(*v0, mask_end, v2);
                        MASK_L(*v0, mask_end, *v0);
                        MASK_L(*v1, mask_end, v3);
                        *v1 = _mm_or_si128(v2, v3);
                }

                *v1 = _mm_xor_si128(*v1, _mm_clmulepi64_si128(
                                *v0, vfold16, 0x00));
                *v0 = _mm_xor_si128(*v1, _mm_clmulepi64_si128(
                                *v0, vfold16, 0x11));
                *v1 = _mm_srli_si128(*v0, 8);
        }
}


/////////////////////
// x86 CLMUL CRC32 //
/////////////////////

/*
// These functions were used to generate the constants
// at the top of crc32_arch_optimized().
static uint64_t
calc_lo(uint64_t p, uint64_t a, int n)
{
        uint64_t b = 0; int i;
        for (i = 0; i < n; i++) {
                b = b >> 1 | (a & 1) << (n - 1);
                a = (a >> 1) ^ ((0 - (a & 1)) & p);
        }
        return b;
}

// same as ~crc(&a, sizeof(a), ~0)
static uint64_t
calc_hi(uint64_t p, uint64_t a, int n)
{
        int i;
        for (i = 0; i < n; i++)
                a = (a >> 1) ^ ((0 - (a & 1)) & p);
        return a;
}
*/

#ifdef BUILDING_CRC32_CLMUL

crc_attr_target
crc_attr_no_sanitize_address
static uint32_t
crc32_arch_optimized(const uint8_t *buf, size_t size, uint32_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
        // The code assumes that there is at least one byte of input.
        if (size == 0)
                return crc;
#endif

        // uint32_t poly = 0xedb88320;
        const int64_t p = 0x1db710640; // p << 1
        const int64_t mu = 0x1f7011641; // calc_lo(p, p, 32) << 1 | 1
        const int64_t k5 = 0x163cd6124; // calc_hi(p, p, 32) << 1
        const int64_t k4 = 0x0ccaa009e; // calc_hi(p, p, 64) << 1
        const int64_t k3 = 0x1751997d0; // calc_hi(p, p, 128) << 1

        const __m128i vfold4 = _mm_set_epi64x(mu, p);
        const __m128i vfold8 = _mm_set_epi64x(0, k5);
        const __m128i vfold16 = _mm_set_epi64x(k4, k3);

        __m128i v0, v1, v2;

        crc_simd_body(buf, size, &v0, &v1, vfold16,
                        _mm_cvtsi32_si128((int32_t)~crc));

        v1 = _mm_xor_si128(
                        _mm_clmulepi64_si128(v0, vfold16, 0x10), v1); // xxx0
        v2 = _mm_shuffle_epi32(v1, 0xe7); // 0xx0
        v0 = _mm_slli_epi64(v1, 32);  // [0]
        v0 = _mm_clmulepi64_si128(v0, vfold8, 0x00);
        v0 = _mm_xor_si128(v0, v2);   // [1] [2]
        v2 = _mm_clmulepi64_si128(v0, vfold4, 0x10);
        v2 = _mm_clmulepi64_si128(v2, vfold4, 0x00);
        v0 = _mm_xor_si128(v0, v2);   // [2]
        return ~(uint32_t)_mm_extract_epi32(v0, 2);
}
#endif // BUILDING_CRC32_CLMUL


/////////////////////
// x86 CLMUL CRC64 //
/////////////////////

/*
// These functions were used to generate the constants
// at the top of crc64_arch_optimized().
static uint64_t
calc_lo(uint64_t poly)
{
        uint64_t a = poly;
        uint64_t b = 0;

        for (unsigned i = 0; i < 64; ++i) {
                b = (b >> 1) | (a << 63);
                a = (a >> 1) ^ (a & 1 ? poly : 0);
        }

        return b;
}

static uint64_t
calc_hi(uint64_t poly, uint64_t a)
{
        for (unsigned i = 0; i < 64; ++i)
                a = (a >> 1) ^ (a & 1 ? poly : 0);

        return a;
}
*/

#ifdef BUILDING_CRC64_CLMUL

// 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.
// Trying to workaround the problem with "__asm mov ebx, ebx" didn't help.
// The following pragma works and performance is still good. x86-64 builds
// and CRC32 CLMUL aren't affected by this problem. The problem does not
// happen in crc_simd_body() either (which is shared with CRC32 CLMUL anyway).
//
// NOTE: Another pragma after crc64_arch_optimized() restores
// the optimizations. If the #if condition here is updated,
// the other one must be updated too.
#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && !defined(__clang__) \
                && defined(_M_IX86)
#       pragma optimize("g", off)
#endif

crc_attr_target
crc_attr_no_sanitize_address
static uint64_t
crc64_arch_optimized(const uint8_t *buf, size_t size, uint64_t crc)
{
#ifndef CRC_USE_GENERIC_FOR_SMALL_INPUTS
        // The code assumes that there is at least one byte of input.
        if (size == 0)
                return crc;
#endif

        // const uint64_t poly = 0xc96c5795d7870f42; // CRC polynomial
        const uint64_t p  = 0x92d8af2baf0e1e85; // (poly << 1) | 1
        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 vfold8 = _mm_set_epi64x((int64_t)p, (int64_t)mu);
        const __m128i vfold16 = _mm_set_epi64x((int64_t)k2, (int64_t)k1);

        __m128i v0, v1, v2;

#if defined(__i386__) || defined(_M_IX86)
        crc_simd_body(buf, size, &v0, &v1, vfold16,
                        _mm_set_epi64x(0, (int64_t)~crc));
#else
        // GCC and Clang would produce good code with _mm_set_epi64x
        // but MSVC needs _mm_cvtsi64_si128 on x86-64.
        crc_simd_body(buf, size, &v0, &v1, vfold16,
                        _mm_cvtsi64_si128((int64_t)~crc));
#endif

        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) |
                        (uint64_t)(uint32_t)_mm_extract_epi32(v0, 2));
#else
        return ~(uint64_t)_mm_extract_epi64(v0, 1);
#endif
}

#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && !defined(__clang__) \
                && defined(_M_IX86)
#       pragma optimize("", on)
#endif

#endif // BUILDING_CRC64_CLMUL


// Inlining this function duplicates the function body in crc32_resolve() and
// crc64_resolve(), but this is acceptable because this is a tiny function.
static inline bool
is_arch_extension_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 decoding 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.
}