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// SPDX-License-Identifier: 0BSD
///////////////////////////////////////////////////////////////////////////////
//
/// \file memcmplen.h
/// \brief Optimized comparison of two buffers
//
// Author: Lasse Collin
//
///////////////////////////////////////////////////////////////////////////////
#ifndef LZMA_MEMCMPLEN_H
#define LZMA_MEMCMPLEN_H
#include "common.h"
#ifdef HAVE_IMMINTRIN_H
# include <immintrin.h>
#endif
// Only include <intrin.h> if it is needed. The header is only needed
// on Windows when using an MSVC compatible compiler. The Intel compiler
// can use the intrinsics without the header file.
#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
&& defined(_MSC_VER) \
&& (defined(_M_X64) \
|| defined(_M_ARM64) || defined(_M_ARM64EC)) \
&& !defined(__INTEL_COMPILER)
# include <intrin.h>
#endif
/// Find out how many equal bytes the two buffers have.
///
/// \param buf1 First buffer
/// \param buf2 Second buffer
/// \param len How many bytes have already been compared and will
/// be assumed to match
/// \param limit How many bytes to compare at most, including the
/// already-compared bytes. This must be significantly
/// smaller than UINT32_MAX to avoid integer overflows.
/// Up to LZMA_MEMCMPLEN_EXTRA bytes may be read past
/// the specified limit from both buf1 and buf2.
///
/// \return Number of equal bytes in the buffers is returned.
/// This is always at least len and at most limit.
///
/// \note LZMA_MEMCMPLEN_EXTRA defines how many extra bytes may be read.
/// It's rounded up to 2^n. This extra amount needs to be
/// allocated in the buffers being used. It needs to be
/// initialized too to keep Valgrind quiet.
static lzma_always_inline uint32_t
lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
uint32_t len, uint32_t limit)
{
assert(len <= limit);
assert(limit <= UINT32_MAX / 2);
#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
&& (((TUKLIB_GNUC_REQ(3, 4) || defined(__clang__)) \
&& (defined(__x86_64__) \
|| defined(__aarch64__))) \
|| (defined(__INTEL_COMPILER) && defined(__x86_64__)) \
|| (defined(__INTEL_COMPILER) && defined(_M_X64)) \
|| (defined(_MSC_VER) && (defined(_M_X64) \
|| defined(_M_ARM64) || defined(_M_ARM64EC))))
// This is only for x86-64 and ARM64 for now. This might be fine on
// other 64-bit processors too. On big endian one should use xor
// instead of subtraction and switch to __builtin_clzll().
//
// Reasons to use subtraction instead of xor:
//
// - On some x86-64 processors (Intel Sandy Bridge to Tiger Lake),
// sub+jz and sub+jnz can be fused but xor+jz or xor+jnz cannot.
// Thus using subtraction has potential to be a tiny amount faster
// since the code checks if the quotient is non-zero.
//
// - Some processors (Intel Pentium 4) used to have more ALU
// resources for add/sub instructions than and/or/xor.
//
// The processor info is based on Agner Fog's microarchitecture.pdf
// version 2023-05-26. https://www.agner.org/optimize/
#define LZMA_MEMCMPLEN_EXTRA 8
while (len < limit) {
const uint64_t x = read64ne(buf1 + len) - read64ne(buf2 + len);
if (x != 0) {
// MSVC or Intel C compiler on Windows
# if defined(_MSC_VER) || defined(__INTEL_COMPILER)
unsigned long tmp;
_BitScanForward64(&tmp, x);
len += (uint32_t)tmp >> 3;
// GCC, Clang, or Intel C compiler
# else
len += (uint32_t)__builtin_ctzll(x) >> 3;
# endif
return my_min(len, limit);
}
len += 8;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
&& defined(HAVE__MM_MOVEMASK_EPI8) \
&& (defined(__SSE2__) \
|| (defined(_MSC_VER) && defined(_M_IX86_FP) \
&& _M_IX86_FP >= 2))
// NOTE: This will use 128-bit unaligned access which
// TUKLIB_FAST_UNALIGNED_ACCESS wasn't meant to permit,
// but it's convenient here since this is x86-only.
//
// SSE2 version for 32-bit and 64-bit x86. On x86-64 the above
// version is sometimes significantly faster and sometimes
// slightly slower than this SSE2 version, so this SSE2
// version isn't used on x86-64.
# define LZMA_MEMCMPLEN_EXTRA 16
while (len < limit) {
const uint32_t x = 0xFFFF ^ (uint32_t)_mm_movemask_epi8(
_mm_cmpeq_epi8(
_mm_loadu_si128((const __m128i *)(buf1 + len)),
_mm_loadu_si128((const __m128i *)(buf2 + len))));
if (x != 0) {
len += ctz32(x);
return my_min(len, limit);
}
len += 16;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && !defined(WORDS_BIGENDIAN)
// Generic 32-bit little endian method
# define LZMA_MEMCMPLEN_EXTRA 4
while (len < limit) {
uint32_t x = read32ne(buf1 + len) - read32ne(buf2 + len);
if (x != 0) {
if ((x & 0xFFFF) == 0) {
len += 2;
x >>= 16;
}
if ((x & 0xFF) == 0)
++len;
return my_min(len, limit);
}
len += 4;
}
return limit;
#elif defined(TUKLIB_FAST_UNALIGNED_ACCESS) && defined(WORDS_BIGENDIAN)
// Generic 32-bit big endian method
# define LZMA_MEMCMPLEN_EXTRA 4
while (len < limit) {
uint32_t x = read32ne(buf1 + len) ^ read32ne(buf2 + len);
if (x != 0) {
if ((x & 0xFFFF0000) == 0) {
len += 2;
x <<= 16;
}
if ((x & 0xFF000000) == 0)
++len;
return my_min(len, limit);
}
len += 4;
}
return limit;
#else
// Simple portable version that doesn't use unaligned access.
# define LZMA_MEMCMPLEN_EXTRA 0
while (len < limit && buf1[len] == buf2[len])
++len;
return len;
#endif
}
#endif
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