bitmanipulation.h

#ifndef SIMDJSON_FALLBACK_BITMANIPULATION_H
#define SIMDJSON_FALLBACK_BITMANIPULATION_H
 
#ifndef SIMDJSON_CONDITIONAL_INCLUDE
#include "simdjson/fallback/base.h"
#endif // SIMDJSON_CONDITIONAL_INCLUDE
 
namespace simdjson {
namespace fallback {
namespace {
 
#if defined(_MSC_VER) && !defined(_M_ARM64) && !defined(_M_X64)
static inline unsigned char _BitScanForward64(unsigned long* ret, uint64_t x) {
  unsigned long x0 = (unsigned long)x, top, bottom;
  _BitScanForward(&top, (unsigned long)(x >> 32));
  _BitScanForward(&bottom, x0);
  *ret = x0 ? bottom : 32 + top;
  return x != 0;
}
static unsigned char _BitScanReverse64(unsigned long* ret, uint64_t x) {
  unsigned long x1 = (unsigned long)(x >> 32), top, bottom;
  _BitScanReverse(&top, x1);
  _BitScanReverse(&bottom, (unsigned long)x);
  *ret = x1 ? top + 32 : bottom;
  return x != 0;
}
#endif
 
/* result might be undefined when input_num is zero */
simdjson_inline int leading_zeroes(uint64_t input_num) {
#ifdef _MSC_VER
  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// _MSC_VER
}
 
} // unnamed namespace
} // namespace fallback
} // namespace simdjson
 
#endif // SIMDJSON_FALLBACK_BITMANIPULATION_H