illumos gate

After 10881, the tanh() function in libm.so.2 is no longer returning the correct sign for a negative argument.

Small reproducer:

#include <stdio.h>
#include <math.h>

int
main()
{
        double a;

        a = -1;
        printf("tanh(%f) = %f\n", a, tanh(a));
        a = 1;
        printf("tanh(%f) = %f\n", a, tanh(a));

        return 0;
}

bloody% gcc -m32 -o tanh-32 tanh.c -lm
bloody% gcc -m64 -o tanh-64 tanh.c -lm
bloody% ./tanh-32
tanh(-1.000000) = 0.761594
tanh(1.000000) = 0.761594
bloody% ./tanh-64
tanh(-1.000000) = -0.761594
tanh(1.000000) = 0.761594

This seems to be related to the change to use __builtin_signbit() - if I remove that definition from math_c99.h and rebuild libm, then tanh() produces the correct results.