Merge pull request RustPython#1547 from Writtic/writtic/module_modf

Improve modf module of math

Author: windelbouwman

tests/snippets/stdlib_math.py

@@ -241,3 +241,8 @@ def assertAllNotClose(examples, *args, **kwargs):
 assert math.modf(2.56) == (0.56, 2.0)
 assert math.modf(-2.56) == (-0.56, -2.0)
 assert math.modf(1) == (0.0, 1.0)
+assert math.modf(INF) == (0.0, INF)
+assert math.modf(NINF) == (-0.0, NINF)
+modf_nan = math.modf(NAN)
+assert math.isnan(modf_nan[0])
+assert math.isnan(modf_nan[1])

vm/src/stdlib/math.rs

@@ -264,6 +264,14 @@ fn math_factorial(value: PyIntRef, vm: &VirtualMachine) -> PyResult<BigInt> {
 
 fn math_modf(x: IntoPyFloat, _vm: &VirtualMachine) -> (f64, f64) {
     let x = x.to_f64();
+    if !x.is_finite() {
+        if x.is_infinite() {
+            return (0.0_f64.copysign(x), x);
+        } else if x.is_nan() {
+            return (x, x);
+        }
+    }
+
     (x.fract(), x.trunc())
 }