Update copysign module of math

- Implement copysign function with test case
- Add constants of NAN, INF, NINF on top of `math_module.py`

tests/snippets/math_module.py

@@ -1,6 +1,10 @@
 import math
 from testutils import assert_raises
 
+NAN = float('nan')
+INF = float('inf')
+NINF = float('-inf')
+
 # assert(math.exp(2) == math.exp(2.0))
 # assert(math.exp(True) == math.exp(1.0))
 #
@@ -30,6 +34,37 @@ assert math.trunc(2.2) == 2
 assert math.ceil(3.3) == 4
 assert math.floor(4.4) == 4
 
+assert math.copysign(1, 42) == 1.0
+assert math.copysign(0., 42) == 0.0
+assert math.copysign(1., -42) == -1.0
+assert math.copysign(3, 0.) == 3.0
+assert math.copysign(4., -0.) == -4.0
+assert_raises(TypeError, math.copysign)
+# copysign should let us distinguish signs of zeros
+assert math.copysign(1., 0.) == 1.
+assert math.copysign(1., -0.) == -1.
+assert math.copysign(INF, 0.) == INF
+assert math.copysign(INF, -0.) == NINF
+assert math.copysign(NINF, 0.) == INF
+assert math.copysign(NINF, -0.) == NINF
+# and of infinities
+assert math.copysign(1., INF) == 1.
+assert math.copysign(1., NINF) == -1.
+assert math.copysign(INF, INF) == INF
+assert math.copysign(INF, NINF) == NINF
+assert math.copysign(NINF, INF) == INF
+assert math.copysign(NINF, NINF) == NINF
+assert math.isnan(math.copysign(NAN, 1.))
+assert math.isnan(math.copysign(NAN, INF))
+assert math.isnan(math.copysign(NAN, NINF))
+assert math.isnan(math.copysign(NAN, NAN))
+# copysign(INF, NAN) may be INF or it may be NINF, since
+# we don't know whether the sign bit of NAN is set on any
+# given platform.
+assert math.isinf(math.copysign(INF, NAN))
+# similarly, copysign(2., NAN) could be 2. or -2.
+assert abs(math.copysign(2., NAN)) == 2.
+
 class A(object):
     def __trunc__(self):
         return 2
@@ -91,8 +126,8 @@ assert math.ldexp(0.5, 1) == 1
 assert math.ldexp(0.75, 1) == 1.5
 assert_raises(TypeError, lambda: math.ldexp(None, None))
 
-assert math.frexp(float('inf')) == (float('inf'), 0)
-assert str(math.frexp(float('nan'))) == str((float('nan'), 0))
+assert math.frexp(INF) == (INF, 0)
+assert str(math.frexp(NAN)) == str((NAN, 0))
 assert_raises(TypeError, lambda: math.frexp(None))
 
 assert math.gcd(0, 0) == 0

vm/src/stdlib/math.rs

@@ -40,6 +40,16 @@ make_math_func_bool!(math_isfinite, is_finite);
 make_math_func_bool!(math_isinf, is_infinite);
 make_math_func_bool!(math_isnan, is_nan);
 
+fn math_copysign(a: IntoPyFloat, b: IntoPyFloat, _vm: &VirtualMachine) -> f64 {
+    let a = a.to_f64();
+    let b = b.to_f64();
+    if a.is_nan() || b.is_nan(){
+        a
+    } else {
+        a.copysign(b)
+    }
+}
+
 // Power and logarithmic functions:
 make_math_func!(math_exp, exp);
 make_math_func!(math_expm1, exp_m1);
@@ -213,6 +223,7 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
         "isfinite" => ctx.new_rustfunc(math_isfinite),
         "isinf" => ctx.new_rustfunc(math_isinf),
         "isnan" => ctx.new_rustfunc(math_isnan),
+        "copysign" => ctx.new_rustfunc(math_copysign),
 
         // Power and logarithmic functions:
         "exp" => ctx.new_rustfunc(math_exp),