Write minus sign without a branch

src/lib.rs

@@ -171,10 +171,11 @@ macro_rules! impl_Integer {
                     self.unsigned_abs(),
                     (&mut buf[offset..]).try_into().unwrap(),
                 );
-                if self < 0 {
-                    offset -= 1;
-                    buf[offset].write(b'-');
-                }
+                // Always write the sign and drop it for non-negative values. A
+                // branch here mispredicts on input with mixed signs.
+                // SAFETY: The magnitude has at most MAX_STR_LEN - 1 digits.
+                unsafe { buf.get_unchecked_mut(offset - 1).write(b'-') };
+                offset -= (self < 0) as usize;
                 // SAFETY: Starting from `offset`, all elements of the slice have been set.
                 unsafe { slice_buffer_to_str(buf, offset) }
             }

tests/test.rs

@@ -18,6 +18,8 @@ test! {
     test_u64_half(u64::from(u32::MAX), "4294967295")
     test_u64_max(u64::MAX, "18446744073709551615")
     test_i64_min(i64::MIN, "-9223372036854775808")
+    test_i64_max(i64::MAX, "9223372036854775807")
+    test_i32_neg_1(-1i32, "-1")
 
     test_i16_0(0i16, "0")
     test_i16_min(i16::MIN, "-32768")