-
Notifications
You must be signed in to change notification settings - Fork 6
/
parse_integers_fast.cc
230 lines (202 loc) · 6.86 KB
/
parse_integers_fast.cc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
/* -*- mode: c++; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 4 -*- */
#include <algorithm>
#include <iostream>
#include <iterator>
#include <fstream>
#include <chrono>
#include <cstdio>
#if __cplusplus >= 201703L
#include <charconv>
#endif
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
// https://stackoverflow.com/a/43870188/412080
#define LIKELY(condition) __builtin_expect(static_cast<bool>(condition), 1)
#define UNLIKELY(condition) __builtin_expect(static_cast<bool>(condition), 0)
char const random_ints_filename[] = "random_ints_1600000.txt";
constexpr int ELEMENTS = 1600000;
void method_istream(int(&a)[ELEMENTS]) {
std::ios::sync_with_stdio(false);
int n, m;
std::cin >> n >> m;
for(int i = 0; i < n; ++i)
std::cin >> a[i];
}
void method_scanf(int(&a)[ELEMENTS]) {
int n, m;
if(UNLIKELY(2 != std::scanf("%d %d", &n, &m)))
throw;
for(int i = 0; i < n; ++i)
if(UNLIKELY(1 != std::scanf("%d", a + i)))
throw;
}
constexpr int step = 64;
char const fmt[step * 3] =
"%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d "
"%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d "
"%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d "
"%d %d %d %d %d %d %d %d %d %d %d %d %d %d %d %d"
;
void method_scanf_multi(int(&a)[ELEMENTS]) {
int n, m;
if(UNLIKELY(2 != std::scanf("%d %d", &n, &m)))
throw;
for(int i = 0; i < n; i += step) {
int expected = step < n - i ? step : n - i;
int* b = a + i;
int read = scanf(fmt + 3 * (step - expected),
b + 0x00, b + 0x01, b + 0x02, b + 0x03, b + 0x04, b + 0x05, b + 0x06, b + 0x07,
b + 0x08, b + 0x09, b + 0x0a, b + 0x0b, b + 0x0c, b + 0x0d, b + 0x0e, b + 0x0f,
b + 0x10, b + 0x11, b + 0x12, b + 0x13, b + 0x14, b + 0x15, b + 0x16, b + 0x17,
b + 0x18, b + 0x19, b + 0x1a, b + 0x1b, b + 0x1c, b + 0x1d, b + 0x1e, b + 0x1f,
b + 0x20, b + 0x21, b + 0x22, b + 0x23, b + 0x24, b + 0x25, b + 0x26, b + 0x27,
b + 0x28, b + 0x29, b + 0x2a, b + 0x2b, b + 0x2c, b + 0x2d, b + 0x2e, b + 0x2f,
b + 0x30, b + 0x31, b + 0x32, b + 0x33, b + 0x34, b + 0x35, b + 0x36, b + 0x37,
b + 0x38, b + 0x39, b + 0x3a, b + 0x3b, b + 0x3c, b + 0x3d, b + 0x3e, b + 0x3f);
if(UNLIKELY(read != expected))
throw;
}
}
void method_getchar_inline(int(&a)[ELEMENTS]) {
int n, m;
if(UNLIKELY(2 != std::scanf("%d %d", &n, &m)))
throw;
for(int i = 0; i < n; ++i) {
int r = std::getchar();
while(std::isspace(r))
r = std::getchar();
bool neg = false;
if('-' == r) {
neg = true;
r = std::getchar();
}
r -= '0';
for(;;) {
int s = std::getchar();
if(!std::isdigit(s))
break;
r = r * 10 + (s - '0');
}
a[i] = neg ? -r : r;
}
}
inline int int_parse_inline(char const*& begin, char const* end) {
char const* p = begin;
while(p != end && std::isspace(*p))
++p;
if(UNLIKELY(p == end))
throw;
bool neg = *p == '-';
p += neg;
int r = 0;
do {
unsigned c = *p - '0';
if(c >= 10)
break;
r = r * 10 + static_cast<int>(c);
} while(++p != end);
begin = p;
return neg ? -r : r;
}
template<int(*parse_int)(char const*&, char const*)>
inline void method_mmap_(int(&a)[ELEMENTS]) {
int fd = open(random_ints_filename, O_RDONLY);
if(UNLIKELY(fd == -1))
throw;
struct stat s;
if(UNLIKELY(fstat(fd, &s)))
throw;
void* pfd = mmap(nullptr, s.st_size, PROT_READ, MAP_PRIVATE | MAP_POPULATE, fd, 0);
if(UNLIKELY(pfd == MAP_FAILED))
throw;
char const* begin = static_cast<char const*>(pfd);
char const* end = begin + s.st_size;
int n = parse_int(begin, end);
int m = parse_int(begin, end);
static_cast<void>(m);
for(int i = 0; i < n; ++i)
a[i] = parse_int(begin, end);
}
void method_mmap_inline(int(&a)[ELEMENTS]) {
method_mmap_<int_parse_inline>(a);
}
#if __cplusplus >= 201703L
inline int int_parse_charconv(char const*& begin, char const* end) {
int value;
while(begin != end && std::isspace(*begin))
++begin;
auto r = std::from_chars(begin, end, value);
if(UNLIKELY(static_cast<unsigned>(r.ec)))
throw;
begin = r.ptr;
return value;
}
void method_mmap_charconv(int(&a)[ELEMENTS]) {
method_mmap_<int_parse_charconv>(a);
}
#endif
unsigned reverse_crc32(int const* begin, int const* end) {
unsigned r = 0;
while(begin != end)
r = __builtin_ia32_crc32si(r, *--end);
return r;
}
decltype(&method_istream) const methods[] = {
&method_istream
, &method_scanf
, &method_scanf_multi
, &method_getchar_inline
, &method_mmap_inline
#if __cplusplus >= 201703L
, &method_mmap_charconv
#endif
};
char const* names[] = {
"iostream"
, "scanf"
, "scanf-multi"
, "getchar-inline"
, "mmap-inline"
#if __cplusplus >= 201703L
, "mmap-charconv"
#endif
};
constexpr int method_count = sizeof methods / sizeof *methods;
int main() {
constexpr int RUNS = 10;
printf("method,checksum,seconds\n");
double best_times[method_count];
for(int method = 0; method < method_count; ++method) {
for(int run = 0; run < RUNS; ++run) {
std::ifstream random_ints(random_ints_filename);
auto old_buf = std::cin.rdbuf(random_ints.rdbuf());
if(UNLIKELY(!freopen(random_ints_filename, "rb", stdin)))
throw;
auto t0 = std::chrono::high_resolution_clock::now();
int a[ELEMENTS];
methods[method](a);
auto t1 = std::chrono::high_resolution_clock::now();
// Make sure the array and the computations are not optimized away.
unsigned sum = reverse_crc32(a, a + sizeof a / sizeof *a);
double time = std::chrono::duration_cast<std::chrono::duration<double>>(t1 - t0).count();
std::printf("%s,%u,%.9f\n", names[method], sum, time);
if(!run || time < best_times[method])
best_times[method] = time;
std::cin.rdbuf(old_buf);
}
}
std::printf("\n---- Best times ----\n");
std::printf("seconds, percent, method\n");
int indexes[method_count];
for(int i = 0; i < method_count; ++i)
indexes[i] = i;
std::sort(indexes, indexes + method_count, [&best_times](int a, int b) { return best_times[a] > best_times[b]; });
int worst = indexes[0];
for(int method = 0; method < method_count; ++method) {
int i = indexes[method];
std::printf("%.9f, %6.1f, %s\n", best_times[i], 1e2 * best_times[i] / best_times[worst], names[i]);
}
}