/cc @billotosyr for the s390x failures.

I'll try disabling the s390x vector implementations of math.Atan, math.Log and math.Log10 tomorrow. I suspect there could be subtle differences in there that are affecting these new tests (Atan looks like a ~1 ulp difference while the Log/Log10 tests look like zero sign differences).

Change https://golang.org/cl/206037 mentions this issue: Revert "math/cmplx: handle special cases"

for s390x

--- FAIL: TestAtan (0.00s)
    cmath_test.go:1018: Atan((1+0i)) = (0.7853981633974484+0i), want (0.7853981633974483+0i)
    cmath_test.go:1026: Atan((1-0i)) = (0.7853981633974484-0i), want (0.7853981633974483-0i)
    cmath_test.go:1030: Atan((-1-0i)) = (-0.7853981633974484-0i), want (-0.7853981633974483-0i)
--- FAIL: TestLog (0.00s)
    cmath_test.go:1163: Log((+Inf-1i)) = (+Inf+0i), want (+Inf-0i)
--- FAIL: TestLog10 (0.00s)
    cmath_test.go:1184: Log10((+Inf-1i)) = (+Inf+0i), want (+Inf-0i)

The first failures are due to the test being too strict for checking the value of math.Atan(re) it should be converted to use cVeryClose instead of cAlike

The failures on Log are actually a discrepancy in s390x handling of math.Atan2(imag(x), real(x))

Log(x) == complex(math.Log(Abs(x)), Phase(x)) == complex(math.Log(Abs(x)), math.Atan2(imag(x), real(x))

so the issue is that math.Atan2(-1, +Inf) should equal -0, but does not on s390x.

Note C99 Annex F. 9.1.4 specifies:

atan2(±y,+∞) returns ± 0 for finite y>0.

But the go documentation for math.Atan2 doesn't actually specify the sign.

// Atan2(y, +Inf) = 0

However, the pure go implementation matches the C99 handling of the sign of zero.

The mips failures

--- FAIL: TestAtan (0.00s)
    cmath_test.go:1030: Atan((-Inf+NaNi)) = (-1.5707963267948966+0i), want (-1.5707963267948966-0i)
--- FAIL: TestCosh (0.00s)
    cmath_test.go:1124: Cosh((-0+NaNi)) = (NaN-0i), want (NaN+0i)
--- FAIL: TestTanh (0.00s)
    cmath_test.go:1357: Tanh((-Inf+NaNi)) = (-1+0i), want (-1-0i)

are due to errors in the test code with respect to NaN sign handling. The tests have cases that check f(x) == f(-x) for appropriate functions, but -x does not necessarily change the sign bit of NaN and math.Copysign should be used instead.

The two issues with the test code are easy fixes, but a decision should be made about the Atan2 special case that disagrees between the Go documentation (s390x implementation) and the C99 standard (pure go implementation).