Public bug reported:
Hello.
I have found that math sin function is unreasonable slow (400us on Athlon64 A2
4800+) for some values. It only happens on 64bit distribution.
Used versions:
Kubuntu 7.10 amd64 gutsy gutter
linux kernel 2.6.24
libc6 2.6.1-1ubuntu10
libc6-dev 2.6.1-1ubuntu10
Some of those values:
-----------------------------------------------------------------------
0.93340582292648832662962377071381 00 b0 6b e3 75 de ed 3f
0x3fedde75e36bb000
2.3328432680770916363144351635128 d0 ad 38 bb a9 a9 02 40
0x4002a9a9bb38add0
3.7439477503636453548097051680088 00 f5 cd e0 9a f3 0d 40
0x400df39ae0cdf500
3.9225160069792437411706487182528 50 19 80 12 50 61 0f 40
0x400f615012801950
4.0711651639931289992091478779912 20 dc 4f 85 df 48 10 40
0x401048df854fdc20
4.7858438478542097982426639646292 c0 2f e9 3f b4 24 13 40
0x401324b43fe92fc0
5.9840767662578002727968851104379 a0 52 df d1 b1 ef 17 40
0x4017efb1d1df52a0
Short program for testing:
------------------------------------------------------------------
#include <stdlib.h>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <math.h>
#include <sys/time.h>
using namespace std;
int main(int argc, char** argv) {
volatile union {
double dbl;
unsigned char hex[sizeof(double)];
} value;
if (argc == sizeof(double)+1) {
for (int i=0; i < sizeof(double); i++) {
istringstream s(argv[i+1]);
int tmp;
s >> hex >> tmp;
value.hex[i] = tmp;
}
} else if (argc == 2) {
istringstream s(argv[1]);
double tmp;
s >> tmp;
value.dbl = tmp;
} else {
cout << "usage: sintest 00 b0 6b e3 75 de ed 3f\n"
" sintest 0.93340582292648832662962377071381";
return (EXIT_FAILURE);
}
cout.precision(32);
cout << value.dbl << endl;
cout << "start\n";
struct timeval time1, time2;
gettimeofday(&time1, NULL);
for (int i=0; i < 10000; i++) {
volatile double out = sin(value.dbl);
}
gettimeofday(&time2, NULL);
long long diftime = 1000000ll * (time2.tv_sec - time1.tv_sec) +
(time2.tv_usec - time1.tv_usec);
cout << "end: " << diftime / 1000000ll << '.' << setw(6) << setfill('0') <<
diftime % 1000000ll << " s" << endl;
return (EXIT_SUCCESS);
}
Petr Cervenka
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
--
slow math sin function for some values on amd64
https://bugs.launchpad.net/bugs/192134
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