1#ifndef SIMDJSON_ARM64_BITMANIPULATION_H
2#define SIMDJSON_ARM64_BITMANIPULATION_H
3
4namespace simdjson {
5namespace SIMDJSON_IMPLEMENTATION {
6namespace {
7
8// We sometimes call trailing_zero on inputs that are zero,
9// but the algorithms do not end up using the returned value.
10// Sadly, sanitizers are not smart enough to figure it out.
11SIMDJSON_NO_SANITIZE_UNDEFINED
12simdjson_inline int trailing_zeroes(uint64_t input_num) {
13#ifdef SIMDJSON_REGULAR_VISUAL_STUDIO
14 unsigned long ret;
15 // Search the mask data from least significant bit (LSB)
16 // to the most significant bit (MSB) for a set bit (1).
17 _BitScanForward64(&ret, input_num);
18 return (int)ret;
19#else // SIMDJSON_REGULAR_VISUAL_STUDIO
20 return __builtin_ctzll(input_num);
21#endif // SIMDJSON_REGULAR_VISUAL_STUDIO
22}
23
24/* result might be undefined when input_num is zero */
25simdjson_inline uint64_t clear_lowest_bit(uint64_t input_num) {
26 return input_num & (input_num-1);
27}
28
29/* result might be undefined when input_num is zero */
30simdjson_inline int leading_zeroes(uint64_t input_num) {
31#ifdef SIMDJSON_REGULAR_VISUAL_STUDIO
32 unsigned long leading_zero = 0;
33 // Search the mask data from most significant bit (MSB)
34 // to least significant bit (LSB) for a set bit (1).
35 if (_BitScanReverse64(&leading_zero, input_num))
36 return (int)(63 - leading_zero);
37 else
38 return 64;
39#else
40 return __builtin_clzll(input_num);
41#endif// SIMDJSON_REGULAR_VISUAL_STUDIO
42}
43
44/* result might be undefined when input_num is zero */
45simdjson_inline int count_ones(uint64_t input_num) {
46 return vaddv_u8(p0: vcnt_u8(vcreate_u8(input_num)));
47}
48
49
50#if defined(__GNUC__) // catches clang and gcc
51/**
52 * ARM has a fast 64-bit "bit reversal function" that is handy. However,
53 * it is not generally available as an intrinsic function under Visual
54 * Studio (though this might be changing). Even under clang/gcc, we
55 * apparently need to invoke inline assembly.
56 */
57/*
58 * We use SIMDJSON_PREFER_REVERSE_BITS as a hint that algorithms that
59 * work well with bit reversal may use it.
60 */
61#define SIMDJSON_PREFER_REVERSE_BITS 1
62
63/* reverse the bits */
64simdjson_inline uint64_t reverse_bits(uint64_t input_num) {
65 uint64_t rev_bits;
66 __asm("rbit %0, %1" : "=r"(rev_bits) : "r"(input_num));
67 return rev_bits;
68}
69
70/**
71 * Flips bit at index 63 - lz. Thus if you have 'leading_zeroes' leading zeroes,
72 * then this will set to zero the leading bit. It is possible for leading_zeroes to be
73 * greating or equal to 63 in which case we trigger undefined behavior, but the output
74 * of such undefined behavior is never used.
75 **/
76SIMDJSON_NO_SANITIZE_UNDEFINED
77simdjson_inline uint64_t zero_leading_bit(uint64_t rev_bits, int leading_zeroes) {
78 return rev_bits ^ (uint64_t(0x8000000000000000) >> leading_zeroes);
79}
80
81#endif
82
83simdjson_inline bool add_overflow(uint64_t value1, uint64_t value2, uint64_t *result) {
84#ifdef SIMDJSON_REGULAR_VISUAL_STUDIO
85 *result = value1 + value2;
86 return *result < value1;
87#else
88 return __builtin_uaddll_overflow(value1, value2,
89 reinterpret_cast<unsigned long long *>(result));
90#endif
91}
92
93} // unnamed namespace
94} // namespace SIMDJSON_IMPLEMENTATION
95} // namespace simdjson
96
97#endif // SIMDJSON_ARM64_BITMANIPULATION_H
98