diff options
Diffstat (limited to 'nacl/cpucycles/x86estimate.c')
-rw-r--r-- | nacl/cpucycles/x86estimate.c | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/nacl/cpucycles/x86estimate.c b/nacl/cpucycles/x86estimate.c new file mode 100644 index 00000000..e5ae66cf --- /dev/null +++ b/nacl/cpucycles/x86estimate.c | |||
@@ -0,0 +1,59 @@ | |||
1 | #include <time.h> | ||
2 | #include <sys/time.h> | ||
3 | #include <sys/types.h> | ||
4 | #include <sys/sysctl.h> | ||
5 | |||
6 | long long cpucycles_x86estimate(void) | ||
7 | { | ||
8 | long long result; | ||
9 | asm volatile(".byte 15;.byte 49" : "=A" (result)); | ||
10 | return result; | ||
11 | } | ||
12 | |||
13 | static long long microseconds(void) | ||
14 | { | ||
15 | struct timeval t; | ||
16 | gettimeofday(&t,(struct timezone *) 0); | ||
17 | return t.tv_sec * (long long) 1000000 + t.tv_usec; | ||
18 | } | ||
19 | |||
20 | static double guessfreq(void) | ||
21 | { | ||
22 | long long tb0; long long us0; | ||
23 | long long tb1; long long us1; | ||
24 | |||
25 | tb0 = cpucycles_x86estimate(); | ||
26 | us0 = microseconds(); | ||
27 | do { | ||
28 | tb1 = cpucycles_x86estimate(); | ||
29 | us1 = microseconds(); | ||
30 | } while (us1 - us0 < 10000 || tb1 - tb0 < 1000); | ||
31 | if (tb1 <= tb0) return 0; | ||
32 | tb1 -= tb0; | ||
33 | us1 -= us0; | ||
34 | return ((double) tb1) / (0.000001 * (double) us1); | ||
35 | } | ||
36 | |||
37 | static double cpufrequency = 0; | ||
38 | |||
39 | static void init(void) | ||
40 | { | ||
41 | double guess1; | ||
42 | double guess2; | ||
43 | int loop; | ||
44 | |||
45 | for (loop = 0;loop < 100;++loop) { | ||
46 | guess1 = guessfreq(); | ||
47 | guess2 = guessfreq(); | ||
48 | if (guess1 > 1.01 * guess2) continue; | ||
49 | if (guess2 > 1.01 * guess1) continue; | ||
50 | cpufrequency = 0.5 * (guess1 + guess2); | ||
51 | break; | ||
52 | } | ||
53 | } | ||
54 | |||
55 | long long cpucycles_x86estimate_persecond(void) | ||
56 | { | ||
57 | if (!cpufrequency) init(); | ||
58 | return cpufrequency; | ||
59 | } | ||