bitmanipulation.h

#ifndef SIMDJSON_ARM64_BITMANIPULATION_H
#define SIMDJSON_ARM64_BITMANIPULATION_H
 
#ifndef SIMDJSON_CONDITIONAL_INCLUDE
#include "simdjson/arm64/base.h"
#include "simdjson/arm64/intrinsics.h"
#endif // SIMDJSON_CONDITIONAL_INCLUDE
 
namespace simdjson {
namespace arm64 {
namespace {
 
// We sometimes call trailing_zero on inputs that are zero,
// but the algorithms do not end up using the returned value.
// Sadly, sanitizers are not smart enough to figure it out.
SIMDJSON_NO_SANITIZE_UNDEFINED
// This function can be used safely even if not all bytes have been
// initialized.
// See issue https://github.com/simdjson/simdjson/issues/1965
SIMDJSON_NO_SANITIZE_MEMORY
simdjson_inline int trailing_zeroes(uint64_t input_num) {
#if SIMDJSON_REGULAR_VISUAL_STUDIO
  unsigned long ret;
  // Search the mask data from least significant bit (LSB)
  // to the most significant bit (MSB) for a set bit (1).
  _BitScanForward64(&ret, input_num);
  return (int)ret;
#else // SIMDJSON_REGULAR_VISUAL_STUDIO
  return __builtin_ctzll(input_num);
#endif // SIMDJSON_REGULAR_VISUAL_STUDIO
}
 
/* result might be undefined when input_num is zero */
simdjson_inline uint64_t clear_lowest_bit(uint64_t input_num) {
  return input_num & (input_num-1);
}
 
// We sometimes call leading_zeroes on inputs that are zero,
// but the algorithms do not end up using the returned value.
// Sadly, sanitizers are not smart enough to figure it out.
// Applies only when SIMDJSON_PREFER_REVERSE_BITS is defined and true.
// (See below.)
SIMDJSON_NO_SANITIZE_UNDEFINED
/* result might be undefined when input_num is zero */
simdjson_inline int leading_zeroes(uint64_t input_num) {
#if SIMDJSON_REGULAR_VISUAL_STUDIO
  unsigned long leading_zero = 0;
  // Search the mask data from most significant bit (MSB)
  // to least significant bit (LSB) for a set bit (1).
  if (_BitScanReverse64(&leading_zero, input_num))
    return (int)(63 - leading_zero);
  else
    return 64;
#else
  return __builtin_clzll(input_num);
#endif// SIMDJSON_REGULAR_VISUAL_STUDIO
}
 
/* result might be undefined when input_num is zero */
simdjson_inline int count_ones(uint64_t input_num) {
   return vaddv_u8(vcnt_u8(vcreate_u8(input_num)));
}
 
 
#if defined(__GNUC__) // catches clang and gcc
/*
 * We use SIMDJSON_PREFER_REVERSE_BITS as a hint that algorithms that
 * work well with bit reversal may use it.
 */
#define SIMDJSON_PREFER_REVERSE_BITS 1
 
/* reverse the bits */
simdjson_inline uint64_t reverse_bits(uint64_t input_num) {
  uint64_t rev_bits;
  __asm("rbit %0, %1" : "=r"(rev_bits) : "r"(input_num));
  return rev_bits;
}
 
SIMDJSON_NO_SANITIZE_UNDEFINED
simdjson_inline uint64_t zero_leading_bit(uint64_t rev_bits, int leading_zeroes) {
  return rev_bits ^ (uint64_t(0x8000000000000000) >> leading_zeroes);
}
 
#endif
 
simdjson_inline bool add_overflow(uint64_t value1, uint64_t value2, uint64_t *result) {
#if SIMDJSON_REGULAR_VISUAL_STUDIO
  *result = value1 + value2;
  return *result < value1;
#else
  return __builtin_uaddll_overflow(value1, value2,
                                   reinterpret_cast<unsigned long long *>(result));
#endif
}
 
} // unnamed namespace
} // namespace arm64
} // namespace simdjson
 
#endif // SIMDJSON_ARM64_BITMANIPULATION_H