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liblzma: Use 8-byte method in memcmplen.h on ARM64.
It requires fast unaligned access to 64-bit integers and a fast instruction to count leading zeros in a 64-bit integer (__builtin_ctzll()). This perhaps should be enabled on some other archs too. Thanks to Chenxi Mao for the original patch: https://github.com/tukaani-project/xz/pull/75 (the first commit) According to the numbers there, this may improve encoding speed by about 3-5 %. This enables the 8-byte method on MSVC ARM64 too which should work but wasn't tested.
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1 changed files with 10 additions and 8 deletions
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@ -24,7 +24,8 @@
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// can use the intrinsics without the header file.
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#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
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&& defined(_MSC_VER) \
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&& defined(_M_X64) \
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&& (defined(_M_X64) \
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|| defined(_M_ARM64) || defined(_M_ARM64EC)) \
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&& !defined(__INTEL_COMPILER)
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# include <intrin.h>
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#endif
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@ -58,20 +59,21 @@ lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
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#if defined(TUKLIB_FAST_UNALIGNED_ACCESS) \
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&& (((TUKLIB_GNUC_REQ(3, 4) || defined(__clang__)) \
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&& defined(__x86_64__)) \
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&& (defined(__x86_64__) \
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|| defined(__aarch64__))) \
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|| (defined(__INTEL_COMPILER) && defined(__x86_64__)) \
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|| (defined(__INTEL_COMPILER) && defined(_M_X64)) \
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|| (defined(_MSC_VER) && defined(_M_X64)))
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// I keep this x86-64 only for now since that's where I know this
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// to be a good method. This may be fine on other 64-bit CPUs too.
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// On big endian one should use xor instead of subtraction and switch
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// to __builtin_clzll().
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|| (defined(_MSC_VER) && (defined(_M_X64) \
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|| defined(_M_ARM64) || defined(_M_ARM64EC))))
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// This is only for x86-64 and ARM64 for now. This might be fine on
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// other 64-bit processors too. On big endian one should use xor
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// instead of subtraction and switch to __builtin_clzll().
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#define LZMA_MEMCMPLEN_EXTRA 8
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while (len < limit) {
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const uint64_t x = read64ne(buf1 + len) - read64ne(buf2 + len);
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if (x != 0) {
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// MSVC or Intel C compiler on Windows
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# if (defined(_MSC_VER) || defined(__INTEL_COMPILER)) && defined(_M_X64)
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# if defined(_MSC_VER) || defined(__INTEL_COMPILER)
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unsigned long tmp;
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_BitScanForward64(&tmp, x);
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len += (uint32_t)tmp >> 3;
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