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Fix inconsistent rounding of 0.5 when formatted to 0 decimal places #102935

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merged 2 commits into from
Nov 16, 2022
Merged

Fix inconsistent rounding of 0.5 when formatted to 0 decimal places #102935

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8487444
Fix inconsistent rounding of 0.5 when formatted to 0 decimal places
ajtribick Oct 11, 2022
aa9837b
Add tests for rounding of ties during float formatting
ajtribick Oct 20, 2022
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2 changes: 1 addition & 1 deletion library/core/src/num/flt2dec/strategy/dragon.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -366,7 +366,7 @@ pub fn format_exact<'a>(
if order == Ordering::Greater
|| (order == Ordering::Equal
// SAFETY: `buf[len-1]` is initialized.
&& (len == 0 || unsafe { buf[len - 1].assume_init() } & 1 == 1))
&& len > 0 && unsafe { buf[len - 1].assume_init() } & 1 == 1)
{
// if rounding up changes the length, the exponent should also change.
// but we've been requested a fixed number of digits, so do not alter the buffer...
Expand Down
124 changes: 122 additions & 2 deletions library/core/tests/fmt/float.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ fn test_format_f64() {
assert_eq!("10", format!("{:.0}", 9.9f64));
assert_eq!("9.8", format!("{:.1}", 9.849f64));
assert_eq!("9.9", format!("{:.1}", 9.851f64));
assert_eq!("1", format!("{:.0}", 0.5f64));
assert_eq!("0", format!("{:.0}", 0.5f64));
assert_eq!("1.23456789e6", format!("{:e}", 1234567.89f64));
assert_eq!("1.23456789e3", format!("{:e}", 1234.56789f64));
assert_eq!("1.23456789E6", format!("{:E}", 1234567.89f64));
Expand All @@ -24,14 +24,74 @@ fn test_format_f64() {
assert_eq!("1234.6", format!("{:.1?}", 1234.56789f64));
}

#[test]
fn test_format_f64_rounds_ties_to_even() {
assert_eq!("0", format!("{:.0}", 0.5f64));
assert_eq!("2", format!("{:.0}", 1.5f64));
assert_eq!("2", format!("{:.0}", 2.5f64));
assert_eq!("4", format!("{:.0}", 3.5f64));
assert_eq!("4", format!("{:.0}", 4.5f64));
assert_eq!("6", format!("{:.0}", 5.5f64));
assert_eq!("128", format!("{:.0}", 127.5f64));
assert_eq!("128", format!("{:.0}", 128.5f64));
assert_eq!("0.2", format!("{:.1}", 0.25f64));
assert_eq!("0.8", format!("{:.1}", 0.75f64));
assert_eq!("0.12", format!("{:.2}", 0.125f64));
assert_eq!("0.88", format!("{:.2}", 0.875f64));
assert_eq!("0.062", format!("{:.3}", 0.062f64));
assert_eq!("-0", format!("{:.0}", -0.5f64));
assert_eq!("-2", format!("{:.0}", -1.5f64));
assert_eq!("-2", format!("{:.0}", -2.5f64));
assert_eq!("-4", format!("{:.0}", -3.5f64));
assert_eq!("-4", format!("{:.0}", -4.5f64));
assert_eq!("-6", format!("{:.0}", -5.5f64));
assert_eq!("-128", format!("{:.0}", -127.5f64));
assert_eq!("-128", format!("{:.0}", -128.5f64));
assert_eq!("-0.2", format!("{:.1}", -0.25f64));
assert_eq!("-0.8", format!("{:.1}", -0.75f64));
assert_eq!("-0.12", format!("{:.2}", -0.125f64));
assert_eq!("-0.88", format!("{:.2}", -0.875f64));
assert_eq!("-0.062", format!("{:.3}", -0.062f64));

assert_eq!("2e0", format!("{:.0e}", 1.5f64));
assert_eq!("2e0", format!("{:.0e}", 2.5f64));
assert_eq!("4e0", format!("{:.0e}", 3.5f64));
assert_eq!("4e0", format!("{:.0e}", 4.5f64));
assert_eq!("6e0", format!("{:.0e}", 5.5f64));
assert_eq!("1.28e2", format!("{:.2e}", 127.5f64));
assert_eq!("1.28e2", format!("{:.2e}", 128.5f64));
assert_eq!("-2e0", format!("{:.0e}", -1.5f64));
assert_eq!("-2e0", format!("{:.0e}", -2.5f64));
assert_eq!("-4e0", format!("{:.0e}", -3.5f64));
assert_eq!("-4e0", format!("{:.0e}", -4.5f64));
assert_eq!("-6e0", format!("{:.0e}", -5.5f64));
assert_eq!("-1.28e2", format!("{:.2e}", -127.5f64));
assert_eq!("-1.28e2", format!("{:.2e}", -128.5f64));

assert_eq!("2E0", format!("{:.0E}", 1.5f64));
assert_eq!("2E0", format!("{:.0E}", 2.5f64));
assert_eq!("4E0", format!("{:.0E}", 3.5f64));
assert_eq!("4E0", format!("{:.0E}", 4.5f64));
assert_eq!("6E0", format!("{:.0E}", 5.5f64));
assert_eq!("1.28E2", format!("{:.2E}", 127.5f64));
assert_eq!("1.28E2", format!("{:.2E}", 128.5f64));
assert_eq!("-2E0", format!("{:.0E}", -1.5f64));
assert_eq!("-2E0", format!("{:.0E}", -2.5f64));
assert_eq!("-4E0", format!("{:.0E}", -3.5f64));
assert_eq!("-4E0", format!("{:.0E}", -4.5f64));
assert_eq!("-6E0", format!("{:.0E}", -5.5f64));
assert_eq!("-1.28E2", format!("{:.2E}", -127.5f64));
assert_eq!("-1.28E2", format!("{:.2E}", -128.5f64));
}

#[test]
fn test_format_f32() {
assert_eq!("1", format!("{:.0}", 1.0f32));
assert_eq!("9", format!("{:.0}", 9.4f32));
assert_eq!("10", format!("{:.0}", 9.9f32));
assert_eq!("9.8", format!("{:.1}", 9.849f32));
assert_eq!("9.9", format!("{:.1}", 9.851f32));
assert_eq!("1", format!("{:.0}", 0.5f32));
assert_eq!("0", format!("{:.0}", 0.5f32));
assert_eq!("1.2345679e6", format!("{:e}", 1234567.89f32));
assert_eq!("1.2345679e3", format!("{:e}", 1234.56789f32));
assert_eq!("1.2345679E6", format!("{:E}", 1234567.89f32));
Expand All @@ -50,6 +110,66 @@ fn test_format_f32() {
assert_eq!("1234.6", format!("{:.1?}", 1234.56789f32));
}

#[test]
fn test_format_f32_rounds_ties_to_even() {
assert_eq!("0", format!("{:.0}", 0.5f32));
assert_eq!("2", format!("{:.0}", 1.5f32));
assert_eq!("2", format!("{:.0}", 2.5f32));
assert_eq!("4", format!("{:.0}", 3.5f32));
assert_eq!("4", format!("{:.0}", 4.5f32));
assert_eq!("6", format!("{:.0}", 5.5f32));
assert_eq!("128", format!("{:.0}", 127.5f32));
assert_eq!("128", format!("{:.0}", 128.5f32));
assert_eq!("0.2", format!("{:.1}", 0.25f32));
assert_eq!("0.8", format!("{:.1}", 0.75f32));
assert_eq!("0.12", format!("{:.2}", 0.125f32));
assert_eq!("0.88", format!("{:.2}", 0.875f32));
assert_eq!("0.062", format!("{:.3}", 0.062f32));
assert_eq!("-0", format!("{:.0}", -0.5f32));
assert_eq!("-2", format!("{:.0}", -1.5f32));
assert_eq!("-2", format!("{:.0}", -2.5f32));
assert_eq!("-4", format!("{:.0}", -3.5f32));
assert_eq!("-4", format!("{:.0}", -4.5f32));
assert_eq!("-6", format!("{:.0}", -5.5f32));
assert_eq!("-128", format!("{:.0}", -127.5f32));
assert_eq!("-128", format!("{:.0}", -128.5f32));
assert_eq!("-0.2", format!("{:.1}", -0.25f32));
assert_eq!("-0.8", format!("{:.1}", -0.75f32));
assert_eq!("-0.12", format!("{:.2}", -0.125f32));
assert_eq!("-0.88", format!("{:.2}", -0.875f32));
assert_eq!("-0.062", format!("{:.3}", -0.062f32));

assert_eq!("2e0", format!("{:.0e}", 1.5f32));
assert_eq!("2e0", format!("{:.0e}", 2.5f32));
assert_eq!("4e0", format!("{:.0e}", 3.5f32));
assert_eq!("4e0", format!("{:.0e}", 4.5f32));
assert_eq!("6e0", format!("{:.0e}", 5.5f32));
assert_eq!("1.28e2", format!("{:.2e}", 127.5f32));
assert_eq!("1.28e2", format!("{:.2e}", 128.5f32));
assert_eq!("-2e0", format!("{:.0e}", -1.5f32));
assert_eq!("-2e0", format!("{:.0e}", -2.5f32));
assert_eq!("-4e0", format!("{:.0e}", -3.5f32));
assert_eq!("-4e0", format!("{:.0e}", -4.5f32));
assert_eq!("-6e0", format!("{:.0e}", -5.5f32));
assert_eq!("-1.28e2", format!("{:.2e}", -127.5f32));
assert_eq!("-1.28e2", format!("{:.2e}", -128.5f32));

assert_eq!("2E0", format!("{:.0E}", 1.5f32));
assert_eq!("2E0", format!("{:.0E}", 2.5f32));
assert_eq!("4E0", format!("{:.0E}", 3.5f32));
assert_eq!("4E0", format!("{:.0E}", 4.5f32));
assert_eq!("6E0", format!("{:.0E}", 5.5f32));
assert_eq!("1.28E2", format!("{:.2E}", 127.5f32));
assert_eq!("1.28E2", format!("{:.2E}", 128.5f32));
assert_eq!("-2E0", format!("{:.0E}", -1.5f32));
assert_eq!("-2E0", format!("{:.0E}", -2.5f32));
assert_eq!("-4E0", format!("{:.0E}", -3.5f32));
assert_eq!("-4E0", format!("{:.0E}", -4.5f32));
assert_eq!("-6E0", format!("{:.0E}", -5.5f32));
assert_eq!("-1.28E2", format!("{:.2E}", -127.5f32));
assert_eq!("-1.28E2", format!("{:.2E}", -128.5f32));
}

fn is_exponential(s: &str) -> bool {
s.contains("e") || s.contains("E")
}
4 changes: 2 additions & 2 deletions library/core/tests/num/flt2dec/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -138,7 +138,7 @@ where

// check exact rounding for zero- and negative-width cases
let start;
if expected[0] >= b'5' {
if expected[0] > b'5' {
try_fixed!(f(&decoded) => &mut buf, expectedk, b"1", expectedk + 1;
"zero-width rounding-up mismatch for v={v}: \
actual {actual:?}, expected {expected:?}",
Expand Down Expand Up @@ -1007,7 +1007,7 @@ where
assert_eq!(to_string(f, 999.5, Minus, 3), "999.500");
assert_eq!(to_string(f, 999.5, Minus, 30), "999.500000000000000000000000000000");

assert_eq!(to_string(f, 0.5, Minus, 0), "1");
assert_eq!(to_string(f, 0.5, Minus, 0), "0");
assert_eq!(to_string(f, 0.5, Minus, 1), "0.5");
assert_eq!(to_string(f, 0.5, Minus, 2), "0.50");
assert_eq!(to_string(f, 0.5, Minus, 3), "0.500");
Expand Down