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bitmanipulation.h
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45 lines (39 loc) · 1.27 KB
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#ifndef SIMDJSON_FALLBACK_BITMANIPULATION_H
#define SIMDJSON_FALLBACK_BITMANIPULATION_H
#include "simdjson.h"
#include <limits>
namespace {
namespace fallback {
#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 */
really_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
}
} // namespace fallback
} // unnamed namespace
#endif // SIMDJSON_FALLBACK_BITMANIPULATION_H