Auto merge of #116301 - mj10021:issue-115737-fix, r=cuviper

fix rounding issue with exponents in fmt fixes issue #115737 , where the decimal places are rounded incorrectly when formatting scientific notation
rust-lang · Nov 14, 2023 · b917524 · b917524
2 parents ba7c7a3 3f0908f
commit b917524
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Showing 2 changed files with 24 additions and 7 deletions.
diff --git a/library/core/src/fmt/num.rs b/library/core/src/fmt/num.rs
@@ -309,7 309,6 @@ macro_rules! impl_Exp {
  n /= 10;
  exponent = 1;
  }
-
  let (added_precision, subtracted_precision) = match f.precision() {
  Some(fmt_prec) => {
  // number of decimal digits minus 1
@@ -331,9 330,15 @@ macro_rules! impl_Exp {
  let rem = n % 10;
  n /= 10;
  exponent = 1;
- // round up last digit
- if rem >= 5 {
  // round up last digit, round to even on a tie
  if rem > 5 || (rem == 5 && (n % 2 != 0 || subtracted_precision > 1 )) {
  n = 1;
  // if the digit is rounded to the next power
  // instead adjust the exponent
  if n.ilog10() > (n - 1).ilog10() {
  n /= 10;
  exponent = 1;
  }
  }
  }
  (n, exponent, exponent, added_precision)

diff --git a/library/core/tests/fmt/num.rs b/library/core/tests/fmt/num.rs
@@ -128,28 128,40 @@ fn test_format_int_exp_precision() {
  let big_int: u32 = 314_159_265;
  assert_eq!(format!("{big_int:.1e}"), format!("{:.1e}", f64::from(big_int)));
 
- //test adding precision
  // test adding precision
  assert_eq!(format!("{:.10e}", i8::MIN), "-1.2800000000e2");
  assert_eq!(format!("{:.10e}", i16::MIN), "-3.2768000000e4");
  assert_eq!(format!("{:.10e}", i32::MIN), "-2.1474836480e9");
  assert_eq!(format!("{:.20e}", i64::MIN), "-9.22337203685477580800e18");
  assert_eq!(format!("{:.40e}", i128::MIN), "-1.7014118346046923173168730371588410572800e38");
 
- //test rounding
  // test rounding
  assert_eq!(format!("{:.1e}", i8::MIN), "-1.3e2");
  assert_eq!(format!("{:.1e}", i16::MIN), "-3.3e4");
  assert_eq!(format!("{:.1e}", i32::MIN), "-2.1e9");
  assert_eq!(format!("{:.1e}", i64::MIN), "-9.2e18");
  assert_eq!(format!("{:.1e}", i128::MIN), "-1.7e38");
 
- //test huge precision
  // test huge precision
  assert_eq!(format!("{:.1000e}", 1), format!("1.{}e0", "0".repeat(1000)));
  //test zero precision
  assert_eq!(format!("{:.0e}", 1), format!("1e0",));
  assert_eq!(format!("{:.0e}", 35), format!("4e1",));
 
- //test padding with precision (and sign)
  // test padding with precision (and sign)
  assert_eq!(format!("{: 10.3e}", 1), " 1.000e0");
 
  // test precision remains correct when rounding to next power
 
  for i in i16::MIN..=i16::MAX {
  for p in 0..=5 {
  assert_eq!(
  format!("{i:.p$e}"),
  format!("{:.p$e}", f32::from(i)),
  "integer {i} at precision {p}"
  );
  }
  }
 }
 
 #[test]