Merge pull request RustPython#4465 from yt2b/fix_float_mod

Fix float mod

Author: youknowone

Lib/test/test_float.py

@@ -347,8 +347,6 @@ def test_float_ceil(self):
         self.assertRaises(OverflowError, float("inf").__ceil__)
         self.assertRaises(OverflowError, float("-inf").__ceil__)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     @support.requires_IEEE_754
     def test_float_mod(self):
         # Check behaviour of % operator for IEEE 754 special cases.

common/src/float_ops.rs

@@ -336,11 +336,12 @@ pub fn div(v1: f64, v2: f64) -> Option<f64> {
 
 pub fn mod_(v1: f64, v2: f64) -> Option<f64> {
     if v2 != 0.0 {
-        let mut val = v1 % v2;
-        if (val < 0.0) != (v2 < 0.0) {
-            val += v2;
+        let val = v1 % v2;
+        match (v1.signum() as i32, v2.signum() as i32) {
+            (1, 1) | (-1, -1) => Some(val),
+            _ if (v1 == 0.0) || (v1.abs() == v2.abs()) => Some(val.copysign(v2)),
+            _ => Some((val + v2).copysign(v2)),
         }
-        Some(val)
     } else {
         None
     }

extra_tests/snippets/builtin_float.py

@@ -513,3 +513,6 @@ def identical(x, y):
 assert_raises(ValueError, lambda: float('0._'))
 assert_raises(ValueError, lambda: float('_.0'))
 assert_raises(ValueError, lambda: float('._0'))
+
+assert 3.0 % -2.0 == -1.0
+assert -3.0 % 2.0 == 1.0