Use to_bits comparison to check if a float value can be represented as an integer losslessly.

This allows to simplify the code while still maintaining "negative zeros" edge case.
Thanks @JasonHise for the suggestion.

Author: khvzak

mlua-sys/src/lua51/compat.rs

@@ -187,7 +187,7 @@ pub unsafe fn lua_isinteger(L: *mut lua_State, idx: c_int) -> c_int {
         let n = lua_tonumber(L, idx);
         let i = lua_tointeger(L, idx);
         // Lua 5.3+ returns "false" for `-0.0`
-        if (n - i as lua_Number).abs() < lua_Number::EPSILON && !(n == 0.0 && n.is_sign_negative()) {
+        if n.to_bits() == (i as lua_Number).to_bits() {
             return 1;
         }
     }

mlua-sys/src/lua52/compat.rs

@@ -52,7 +52,7 @@ pub unsafe fn lua_isinteger(L: *mut lua_State, idx: c_int) -> c_int {
         let n = lua_tonumber(L, idx);
         let i = lua_tointeger(L, idx);
         // Lua 5.3+ returns "false" for `-0.0`
-        if (n - i as lua_Number).abs() < lua_Number::EPSILON && !(n == 0.0 && n.is_sign_negative()) {
+        if n.to_bits() == (i as lua_Number).to_bits() {
             return 1;
         }
     }

mlua-sys/src/luau/compat.rs

@@ -121,7 +121,7 @@ pub unsafe fn lua_isinteger(L: *mut lua_State, idx: c_int) -> c_int {
         let n = lua_tonumber(L, idx);
         let i = lua_tointeger(L, idx);
         // Lua 5.3+ returns "false" for `-0.0`
-        if (n - i as lua_Number).abs() < lua_Number::EPSILON && !(n == 0.0 && n.is_sign_negative()) {
+        if n.to_bits() == (i as lua_Number).to_bits() {
             return 1;
         }
     }

src/state/raw.rs

@@ -726,13 +726,9 @@ impl RawLua {
             ffi::LUA_TNUMBER => {
                 use crate::types::Number;
 
-                fn same(n: Number, i: Integer) -> bool {
-                    (n - (i as Number)).abs() < Number::EPSILON && !(n == 0.0 && n.is_sign_negative())
-                }
-
                 let n = ffi::lua_tonumber(state, idx);
                 match num_traits::cast(n) {
-                    Some(i) if same(n, i) => Value::Integer(i),
+                    Some(i) if n.to_bits() == (i as Number).to_bits() => Value::Integer(i),
                     _ => Value::Number(n),
                 }
             }

tests/conversion.rs

@@ -372,21 +372,6 @@ fn test_float_from_lua() -> Result<()> {
     // Should fallback to default conversion
     assert_eq!(f.call::<f32>("42.0")?, 42.0);
 
-    // Negative zero
-    let negative_zero = lua.load("return -0.0").eval::<f64>()?;
-    assert_eq!(negative_zero, 0.0);
-    // LuaJIT treats -0.0 as a positive zero
-    #[cfg(not(feature = "luajit"))]
-    assert!(negative_zero.is_sign_negative());
-
-    // In Lua <5.3 all numbers are floats
-    #[cfg(not(any(feature = "lua54", feature = "lua53", feature = "luajit")))]
-    {
-        let negative_zero = lua.load("return -0").eval::<f64>()?;
-        assert_eq!(negative_zero, 0.0);
-        assert!(negative_zero.is_sign_negative());
-    }
-
     Ok(())
 }
 

tests/tests.rs

@@ -602,6 +602,21 @@ fn test_num_conversion() -> Result<()> {
 
     assert_eq!(lua.unpack::<i128>(lua.pack(1i128 << 64)?)?, 1i128 << 64);
 
+    // Negative zero
+    let negative_zero = lua.load("-0.0").eval::<f64>()?;
+    assert_eq!(negative_zero, 0.0);
+    // LuaJIT treats -0.0 as a positive zero
+    #[cfg(not(feature = "luajit"))]
+    assert!(negative_zero.is_sign_negative());
+
+    // In Lua <5.3 all numbers are floats
+    #[cfg(not(any(feature = "lua54", feature = "lua53", feature = "luajit")))]
+    {
+        let negative_zero = lua.load("-0").eval::<f64>()?;
+        assert_eq!(negative_zero, 0.0);
+        assert!(negative_zero.is_sign_negative());
+    }
+
     Ok(())
 }