mirror of
https://github.com/simdjson/simdjson
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halx99
113 lines
3.7 KiB
C++
113 lines
3.7 KiB
C++
#ifndef SIMDJSON_ARM64_BITMANIPULATION_H
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#define SIMDJSON_ARM64_BITMANIPULATION_H
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#ifndef SIMDJSON_CONDITIONAL_INCLUDE
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#include "simdjson/arm64/base.h"
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#include "simdjson/arm64/intrinsics.h"
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#endif // SIMDJSON_CONDITIONAL_INCLUDE
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namespace simdjson {
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namespace arm64 {
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namespace {
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// We sometimes call trailing_zero on inputs that are zero,
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// but the algorithms do not end up using the returned value.
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// Sadly, sanitizers are not smart enough to figure it out.
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SIMDJSON_NO_SANITIZE_UNDEFINED
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// This function can be used safely even if not all bytes have been
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// initialized.
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// See issue https://github.com/simdjson/simdjson/issues/1965
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SIMDJSON_NO_SANITIZE_MEMORY
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simdjson_inline int trailing_zeroes(uint64_t input_num) {
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#if SIMDJSON_REGULAR_VISUAL_STUDIO
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unsigned long ret;
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// Search the mask data from least significant bit (LSB)
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// to the most significant bit (MSB) for a set bit (1).
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_BitScanForward64(&ret, input_num);
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return (int)ret;
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#else // SIMDJSON_REGULAR_VISUAL_STUDIO
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return __builtin_ctzll(input_num);
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#endif // SIMDJSON_REGULAR_VISUAL_STUDIO
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}
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/* result might be undefined when input_num is zero */
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simdjson_inline uint64_t clear_lowest_bit(uint64_t input_num) {
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return input_num & (input_num-1);
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}
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// We sometimes call leading_zeroes on inputs that are zero,
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// but the algorithms do not end up using the returned value.
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// Sadly, sanitizers are not smart enough to figure it out.
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// Applies only when SIMDJSON_PREFER_REVERSE_BITS is defined and true.
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// (See below.)
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SIMDJSON_NO_SANITIZE_UNDEFINED
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/* result might be undefined when input_num is zero */
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simdjson_inline int leading_zeroes(uint64_t input_num) {
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#if SIMDJSON_REGULAR_VISUAL_STUDIO
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unsigned long leading_zero = 0;
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// Search the mask data from most significant bit (MSB)
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// to least significant bit (LSB) for a set bit (1).
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if (_BitScanReverse64(&leading_zero, input_num))
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return (int)(63 - leading_zero);
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else
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return 64;
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#else
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return __builtin_clzll(input_num);
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#endif// SIMDJSON_REGULAR_VISUAL_STUDIO
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}
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/* result might be undefined when input_num is zero */
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simdjson_inline int count_ones(uint64_t input_num) {
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return vaddv_u8(vcnt_u8(vcreate_u8(input_num)));
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}
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#if defined(__GNUC__) // catches clang and gcc
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/**
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* ARM has a fast 64-bit "bit reversal function" that is handy. However,
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* it is not generally available as an intrinsic function under Visual
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* Studio (though this might be changing). Even under clang/gcc, we
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* apparently need to invoke inline assembly.
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*/
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/*
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* We use SIMDJSON_PREFER_REVERSE_BITS as a hint that algorithms that
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* work well with bit reversal may use it.
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*/
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#define SIMDJSON_PREFER_REVERSE_BITS 1
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/* reverse the bits */
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simdjson_inline uint64_t reverse_bits(uint64_t input_num) {
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uint64_t rev_bits;
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__asm("rbit %0, %1" : "=r"(rev_bits) : "r"(input_num));
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return rev_bits;
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}
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/**
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* Flips bit at index 63 - lz. Thus if you have 'leading_zeroes' leading zeroes,
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* then this will set to zero the leading bit. It is possible for leading_zeroes to be
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* greating or equal to 63 in which case we trigger undefined behavior, but the output
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* of such undefined behavior is never used.
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**/
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SIMDJSON_NO_SANITIZE_UNDEFINED
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simdjson_inline uint64_t zero_leading_bit(uint64_t rev_bits, int leading_zeroes) {
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return rev_bits ^ (uint64_t(0x8000000000000000) >> leading_zeroes);
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}
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#endif
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simdjson_inline bool add_overflow(uint64_t value1, uint64_t value2, uint64_t *result) {
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#if SIMDJSON_REGULAR_VISUAL_STUDIO
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*result = value1 + value2;
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return *result < value1;
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#else
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return __builtin_uaddll_overflow(value1, value2,
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reinterpret_cast<unsigned long long *>(result));
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#endif
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}
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} // unnamed namespace
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} // namespace arm64
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} // namespace simdjson
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#endif // SIMDJSON_ARM64_BITMANIPULATION_H
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