printf: make negative values wrap around with unsigned/hex format

eduardorittner · eduardorittner · commit c6a75345c92c · 2025-04-06T11:03:22.000-03:00
To convert from negative to unsigned with overflow, we get the two's complement
representation of the absolute (unsigned) value.
diff --git a/src/uucore/src/lib/features/parser/num_parser.rs b/src/uucore/src/lib/features/parser/num_parser.rs
@@ -11,6 +11,7 @@ use bigdecimal::{
     BigDecimal,
     num_bigint::{BigInt, BigUint, Sign},
 };
+use num_traits::FromPrimitive;
 use num_traits::Signed;
 use num_traits::ToPrimitive;
 use num_traits::Zero;
@@ -166,22 +167,26 @@ impl ExtendedParser for u64 {
                     let (digits, scale) = bd.into_bigint_and_scale();
                     if scale == 0 {
                         let negative = digits.sign() == Sign::Minus;
-                        match u64::try_from(digits) {
+
+                        match u64::try_from(digits.clone()) {
                             Ok(i) => Ok(i),
-                            _ => Err(ExtendedParserError::Overflow(if negative {
-                                // TODO: We should wrap around here #7488
-                                0
-                            } else {
-                                u64::MAX
-                            })),
+                            _ => {
+                                if negative {
+                                    match u64::try_from(digits.into_parts().1) {
+                                        Ok(i) => Ok(!i + 1), // two's complement representation
+                                        _ => Err(ExtendedParserError::Overflow(u64::MAX)),
+                                    }
+                                } else {
+                                    Err(ExtendedParserError::Overflow(u64::MAX))
+                                }
+                            }
                         }
                     } else {
                         // Should not happen.
                         Err(ExtendedParserError::NotNumeric)
                     }
                 }
-                // TODO: Handle -0 too #7488
-                // No other case should not happen.
+                ExtendedBigDecimal::MinusZero => Ok(0),
                 _ => Err(ExtendedParserError::NotNumeric),
             }
         }
@@ -500,10 +505,28 @@ mod tests {
     fn test_decimal_u64() {
         assert_eq!(Ok(123), u64::extended_parse("123"));
         assert_eq!(Ok(u64::MAX), u64::extended_parse(&format!("{}", u64::MAX)));
-        // TODO: We should wrap around here #7488
+        assert_eq!(Ok(0), u64::extended_parse("-0"));
+        assert_eq!(Ok(u64::MAX), u64::extended_parse("-1"));
+        assert_eq!(
+            Ok(u64::MAX / 2 + 1),
+            u64::extended_parse("-9223372036854775808") // i64::MIN
+        );
+        assert_eq!(
+            Ok(1123372036854675616),
+            u64::extended_parse("-17323372036854876000") // 2*i64::MIN
+        );
+        assert_eq!(Ok(1), u64::extended_parse("-18446744073709551615")); // -u64::MAX
+        assert!(matches!(
+            u64::extended_parse("-18446744073709551616"), // -u64::MAX - 1
+            Err(ExtendedParserError::Overflow(u64::MAX))
+        ));
+        assert!(matches!(
+            u64::extended_parse("-92233720368547758150"),
+            Err(ExtendedParserError::Overflow(u64::MAX))
+        ));
         assert!(matches!(
-            u64::extended_parse("-123"),
-            Err(ExtendedParserError::Overflow(0))
+            u64::extended_parse("-170141183460469231731687303715884105729"),
+            Err(ExtendedParserError::Overflow(u64::MAX))
         ));
         assert!(matches!(
             u64::extended_parse(""),
diff --git a/tests/by-util/test_printf.rs b/tests/by-util/test_printf.rs
@@ -668,6 +668,41 @@ fn partial_integer() {
         .stderr_is("printf: '42x23': value not completely converted\n");
 }
 
+#[test]
+fn unsigned_hex_negative_wraparound() {
+    new_ucmd!()
+        .args(&["%x", "-0b100"])
+        .succeeds()
+        .stdout_only("fffffffffffffffc");
+
+    new_ucmd!()
+        .args(&["%x", "-0100"])
+        .succeeds()
+        .stdout_only("ffffffffffffffc0");
+
+    new_ucmd!()
+        .args(&["%x", "-100"])
+        .succeeds()
+        .stdout_only("ffffffffffffff9c");
+
+    new_ucmd!()
+        .args(&["%x", "-0x100"])
+        .succeeds()
+        .stdout_only("ffffffffffffff00");
+
+    new_ucmd!()
+        .args(&["%x", "-92233720368547758150"])
+        .fails_with_code(1)
+        .stdout_is("ffffffffffffffff")
+        .stderr_is("printf: '-92233720368547758150': Numerical result out of range\n");
+
+    new_ucmd!()
+        .args(&["%u", "-1002233720368547758150"])
+        .fails_with_code(1)
+        .stdout_is("18446744073709551615")
+        .stderr_is("printf: '-1002233720368547758150': Numerical result out of range\n");
+}
+
 #[test]
 fn test_overflow() {
     new_ucmd!()
