[llvm-bugs] [Bug 27193] New: std::acos on complex does not agree with C

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27193

            Bug ID: 27193
           Summary: std::acos on complex does not agree with C
           Product: libc++
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: j.o.e.lpublic at gmail.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com
    Classification: Unclassified

Consider the following:
$ clang --version
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin14.5.0
Thread model: posix

$ cat x.cc 
#include <iostream>
#include <complex>

int main()
{
   std::complex<double> x(0,3.14159265359);  
   std::cout << std::acos(x) << std::endl;
   std::cout << std::cos(std::acos(x)) << std::endl;
   return 0;
}

$ clang++ -std=c++11 x.cc
$ ./a.out 
(1.5708,-3.14159)
(7.09802e-16,11.5487)

$ cat z.c 
#include <math.h>
#include <complex.h>
#include <stdio.h>

int main()
{
    complex double z=0+3.14159*I;
    complex double r=cacos(z);
    complex double rr=ccos(r);
    printf("%e %e\n",creal(r),cimag(r));
    printf("%e %e\n",creal(rr), cimag(rr));
    return 0;
}
$ clang -std=c99 z.c
$ ./a.out 
1.570796e+00 -1.862295e+00
2.018773e-16 3.141590e+00

Compiling programs on linux with clang (and gnu standard libs) has C and C++ in
agreement.

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