round to even

Author: mj10021

library/core/src/fmt/num.rs

@@ -330,20 +330,19 @@ macro_rules! impl_Exp {
                 if subtracted_precision != 0 {
                     let rem = n % 10;
                     n /= 10;
+                    let last_digit_odd = n % 2 != 0;
                     exponent += 1;
-                    // round up last digit
-                    if rem >= 5 {
+                    // round up last digit, round to even on a tie
+                    if rem > 5 || (rem == 5 && last_digit_odd) {
                         n += 1;
                         // if the digit is rounded to the next power
                         // instead adjust the exponent
-                        if n % 10 == 0 {
+                        if n.ilog10() > (n - 1).ilog10() {
                             n /= 10;
                             exponent += 1;
                         }
                     }
-                    // n = 100
                 }
-                // assert!(n == 666, "{}\n{}\n{}\n",n, exponent, added_precision);
                 (n, exponent, exponent, added_precision)
             };