gh-123836: Check zero signs in math_testcases.txt (#123854)

Just like cmath_testcases.txt. These tests require IEEE 754 anyway. Correct zero sign for sqrt tests to match math.h convention.

Author: skirpichev

Lib/test/test_math.py

@@ -187,6 +187,9 @@ def result_check(expected, got, ulp_tol=5, abs_tol=0.0):
 
  # Check exactly equal (applies also to strings representing exceptions)
  if got == expected:
+ if not got and not expected:
+ if math.copysign(1, got) != math.copysign(1, expected):
+ return f"expected {expected}, got {got} (zero has wrong sign)"
  return None
 
  failure = "not equal"
@@ -2067,6 +2070,13 @@ def test_testfile(self):
  except OverflowError:
  result = 'OverflowError'
 
+ # C99+ says for math.h's sqrt: If the argument is +∞ or ±0, it is
+ # returned, unmodified. On another hand, for csqrt: If z is ±0+0i,
+ # the result is +0+0i. Lets correct zero sign of er to follow
+ # first convention.
+ if id in ['sqrt0002', 'sqrt0003', 'sqrt1001', 'sqrt1023']:
+ er = math.copysign(er, ar)
+
  # Default tolerances
  ulp_tol, abs_tol = 5, 0.0